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Crevasses – Antarctic Ice Fractures

By Julian Spergel
Antarctic Ice showing crevassing along the edges of flow. photo J. Spergle

Antarctic Ice showing crevassing along the edges of flow. photo J. Spergel

As we prepare for our sixth flight of the season, I wanted to offer a glimpse of one of the types of glacial features that we are observing and studying as we map the Ross Ice Shelf: Crevasses. The word sends shivers down the spine of anyone whose job involves working on a glacier. These cracks through the glacier can be hundreds of feet deep and hidden beneath a thin layer of snow. They are incredibly treacherous and have claimed the lives of many polar explorers and scientists. They also appear quite frequently in our sensor data as we fly our survey flights for Rosetta-Ice.

The Icepod instrument, with the radar blades shown along the front edge, is being used by the Rosetta project to view through the ice to understand the features and thickness. Photo S. Howard

The Icepod instrument, with the radar blades shown along the front edge, is being used by the Rosetta project to view through the ice to understand the features and thickness. Photo S. Howard

Crevasses are fractures in a glacier caused by the stresses of movement. They are like the cracks in the surface of clay as one pulls it apart past the limits of elasticity. They most often occur where the flow of a glacier increases, like in a steep deepening valley, and are thus oriented perpendicular to direction of flow. Crevasses that lie in a cross direction are called ‘transverse crevasses.’ There are also longitudinal crevasses that form parallel to ice flow and at an angle to the valley walls. These form as the glacier widens and the ice is pulled apart. These cracks in the surface of the ice shelf are an easily identifiable marker of areas of high stress within the ice flow. Mapping where crevasses appear is equivalent to mapping where the ice tensional stresses are highest.

Several different types of crevassing are visible in this image including transverse crevasses, as ice flow from different areas collides. photo M. Wearing

Several different types of crevassing are visible in this image including transverse crevasses, as ice flow from different areas collides. photo M. Wearing

On an otherwise featureless ice shelf, crevasses show where the different ice flows merge as they flow towards the open sea. Fahnestock et al. (2000) mapped crevasses, rifts, and glacial stretch marks they call “flow lines” on the Ross Ice Shelf in order to study the flow of ice from different glacial source areas to the Ross Sea and how these patterns may have changed in the past thousand years. From their study of the surface features, they were able to draw lines across the Ross Ice Shelf and identify whether a region of ice shelf was flowing in over the Trans-Antarctic Mountains from East Antarctica, or from the rapidly flowing ice streams from West Antarctica, named from southwest to northeast Ice Streams A, B, C, D, and E. A piece of ice takes about one thousand years to travel from the back of the Ross Ice Shelf to the front, and from its surrounding area we can tell where the piece of ice originated.

Ice streams A, B, C, D and E flowing in from West Antarctica. Image from Rignot et al, 2011

Ice streams A, B, C, D and E flowing in from West Antarctica. Image from Rignot et al, 2011

The Rosetta ice-penetrating radar shows us crevasses deep with in the ice. These cracks formed on the surface and were carried along and buried by centuries of snow and glacial flow. In the radar image, buried crevasses appear as thin arches. As the radar beam penetrates through the snow and ice like ripples in a pond, bouncing off of surfaces of changing density, the sharp corner of a crevasse scatters the ripples. When the radar image is processed from the echoes of the broadcasted signal, this sharp point of scattering becomes an arch descending down from an otherwise flat surface.

Radar images of crevassing in the ice shelf showing the characteristic arch descending down from the flattened surface. Photo J. Spergle

Radar images of crevassing in the ice shelf showing the characteristic arch descending down from the flattened surface. Photo J. Spergle

What do these buried crevasses tell us? Like digging to the bottom of a stack of papers on a desk, these ancient crevasses tell us of past glacial events. Their burial depth divided by the local snow accumulation rates gives an estimate for the period of stagnation required to stop flow, fill and bury the crevasses to the observed depth. They indicate past flow conditions, or even the locations of abandoned shear margins, where there used to be a boundary between ice streams moving at differing speeds.

Close up view showing the strain in the ice as it is pulled by changes in flow speed. photo S. Howard

Close up view showing the strain in the ice as it is pulled by changes in flow speed. photo S. Howard

Lastly, crevasses are interesting because sometimes fascinating things fall into them. A few studies have shown that wind-blown meteorites get caught in snow-filled crevasses. Knowing where to look for rare meteorites is a huge help to our friends in the astro-geology community. Crevasses are also the places where meltwater drains down to the base of the ice. This affects the slipperiness of the glacier’s bed, and can speed up it flow. Meltwater flowing through crevasses also widens the crack, called hydrofracturing. This can further weaken the structural stability around the crevasse, priming the area for a later break. While Rosetta-Ice is not specifically looking for extraterrestrial rocks or draining water, we are on the lookout in our radar data for anything that can tell us about the history or current flow conditions of the Ross Ice Shelf.

Answers to a few of the questions asked by students at East Harlem School:

Is it possible for plants to grow in Antarctica?

Yes, a few. There’s a dozen native species that live on the Antarctic Peninsula, the thin peninsula of land that stretches north into relatively warmer parts of this continent. Everywhere else, only a few lichens, the crinkly stuff that grows on rocks and trees, survive.

How do you survive in the cold? What’s the hardest part about living/being in Antarctica?

With the right warm clothing and the right behavior, Antarctica’s conditions are very survivable. It’s very important to wear the right layers of clothes because you need to both stay warm, but also not let your sweat stay wet against your skin. I wear a thermal underwear layer that is warm and wicks sweat away. On top of that I’ll either wear a warm shirt or a thin sweater. On top of that, I wear a fleece or wool jacket, and then I wear my big red parka. Everyone has one and we call them our “Big Reds.” On my legs, I wear fleece pants and snowpants. I wear two layers of socks usually, and either my boots or the rubber boots that they gave us, called “Bunny Boots.” When I get too cold, I go inside, out of the wind, to warm up.

For me, the hardest part of living in Antarctica is the isolation. I personally use the internet a lot to connect to friends and family, but the combination of the slow internet connection and the time difference makes it difficult.

How has global warming affected how much ice will be there in 5 years?

We’re certain that the warming of ocean water is melting from underneath the floating ice shelves around Antarctica, and we predict that the warming atmosphere will lead to more melting and calving, but how much global warming-caused ice loss might there be within the next five years? There’s no way to know. What we still don’t know about how Antarctica’s climate works could fill a library. Weather over Antarctica is incredibly unpredictable, and we still cannot tell for sure how the multi-year climate cycles affect melting continent-wide. That question, how will global warming effect ice mass loss in Antarctica, is quite literally a multi-million dollar question. Thousands of scientists are studying every aspect of the Antarctic glacial system to get a sense of what is “natural” — what amounts of ice loss and gain are within the normal range of decades- or century-long cycles — and what can be interpreted as a result of human-caused climate change. Hopefully, Rosetta-Ice will yield a small piece of the puzzle.

For more information about Rosetta-Ice, check out our website and the archive of this blog. Have questions about Rosetta-Ice or about living and working in Antarctica? Feel free to email your question to juliansantarctica@gmail.com, and I will try to answer it in the next blog entry!

Julian Spergel is a graduate student at the Department of Earth and Environmental Science at Lamont-Doherty Earth Observatory and will be blogging from Antarctica. He works with Professor Jonathan Kingslake on analyzing spatial and temporal trends of supraglacial lakes on the Antarctic Ice Sheet using satellite imagery.

Flying is Easy, Just Think Happy Thoughts…

By Julian Spergel

As of my writing, we have completed three survey flights.  It feels good to finally be collecting data. The night shift, myself included, has spent the past two days checking the collected data for signs of any instrument breakage or recording errors.

 Susan HowardFlying past the Trans-Antarctic Mountains that line the East side of the Ross Shelf. Photo credit: Susan Howard

Although Peter Pan suggested ‘happy thoughts’ would get us airborne, in Antarctica we are still very much at the will of the weather. Yesterday evening’s flight was cancelled because of fog, and so this morning we wanted to get as much flying in as possible before the late afternoon fog rolled in. Although the morning shift had to wait a bit for the IcePod instruments and the plane to warm up before departing, they were able to complete two full survey lines before their afternoon return. It is early in the season and I haven’t been able to fly a mission yet myself, but I am eagerly waiting for my first opportunity.

 Alec LockettView out of the LC-130 during Monday afternoon’s flight. The aircraft wing is visible in the top left of the photo and the tiny grey spot in the snow is the shadow of the plane. Photo Credit: Alec Lockett

Our daily schedule is not the easiest when we fly. This is especially true for those who need to make decisions about our daily activities. Every day, from 4 to 4:30 AM, Kirsty Tinto, our chief scientist, checks to see if that morning’s flight is going ahead, next she checks in with the team ending their night shift for updates on instrument functioning. At 5 am, she and the day’s flight engineer meet with the weather operations and flight operations team to go over the day’s flight plan considering the weather forecast. The team has to be flexible when building a daily mission that works with the daily weather constraints.

 Susan Howard

Flight Engineer Chris Bertinato monitoring the airborne instruments inside the LC—130 cargo hold. Photo Credit: Susan Howard

Meanwhile, the gravity instrument operators, affectionately called the “graviteers,” go down to the airfield with the aircraft load-masters to oversee the loading of the gravimeter into the plane. Collecting data on minuscule changes to gravity requires that we know exactly where in the plane the instruments sit to calculate accelerations. Although it is tempting to leave the sensitive instruments on the plane overnight, the gravimeters must be kept warm at all times for peak functionality, as a result the gravimeters must be loaded and surveyed at the beginning of every day and unloaded at the end of the day. The plane is readied for take-off with a systems check and the flight crew and our project’s flight engineers prepare for flying.

The non-flight members of our team arrive to Williams Airfield soon after from our base at McMurdo camp. Every shift has an archivist, someone who copies the data from the various digital storage units carried in flight and then carefully transports them back to the tent. The data is transferred to the central computer, as well as to two backup hard drives for redundancy. At the end of the shift, there are nine hard drives and two USB sticks filled with data. The archivist also selects three to four five-minute segments of data for quality control, which we call “QCing”. The other QCers and I look through the segments from every data set for breaks in the data, for anomalies, and for particularly good or interesting segments. Arguably, the most important data set to check is our positioning-navigation-timing system. None of our data is useful if we cannot precisely place where in the world we were when we collected the data. Some of our instruments must also know precisely the angle and velocity of the plane in order to yield useful data. Once that is checked, we look at the data readouts.

Timelapse video of a few hours of night shift “QCing” Credit: Julian Spergel

If there’s anything surprising within the Ross Ice Shelf, we QCers might be the first ones to know…while it is fun to wonder what we could find, what do we actually see? In the radar data, we can see the surface and bed of the ice shelf and often we can see areas of buried crevasses. In the shallow ice radar, we can often see where different ice masses from geographically disparate glacial sources merge as they flow towards the ocean. From LiDar (Light Detection and Ranging), we can see very high detailed maps of the surface of the ice shelf, which can give us information about the flow of the ice and the changing surface climate conditions, i.e. wind and temperature. From gravity and magnetics readings, we can glean information about the size of the cavity under the ice shelf and the ocean bed beneath the water.

An aerial photo from our onboard camera of the edge between the ice and McMurdo Station. Photo by Susan Howard.

An aerial photo from our onboard camera of the edge between the ice and McMurdo Station. At the lower right you can see the circlar shape of a tank. Photo by Susan Howard.

Though we’ve just begun our survey flying, we’re excited to see what our instruments will show us about the Ross Ice Shelf. Weather permitting we will fly day and night this week pushing through being tired. Yes we are tired, and I know I am guilty of getting a little snippy, but we are down at the edge of the world for valuable scientific work. When I see the sun kiss the horizon, and watch the shadows lengthen for a moment and the snow become golden, I know that this experience will end up being incredible.

The mother crab-eater seal nursing her newborn pup. In the background, a skua hungrily eyes the afterbirth. South polar skua are aggressive seabirds,  scavengers and carrion eaters, readily scavenging any food source.

The mother crab-eater seal nursing her newborn pup. In the background, a skua hungrily eyes the afterbirth. South polar skua are aggressive seabirds, scavengers and carrion eaters, readily scavenging any food source. One of our ‘tough’ Alamo floats is named after a south polar skua. 

In non-science news, we saw the birth of a baby crabeater seal on Sunday. Everyone else on the team has named the newborn seal “Rosetta,” but in my mind, the seal’s name is “Boopy.”

For more information about Rosetta-Ice, check out our website and the archive of this blog. Have questions about Rosetta-Ice or about living and working in Antarctica? Feel free to email your question to juliansantarctica@gmail.com, and I will try to answer it in the next blog entry!

Julian Spergel is a graduate student at the Department of Earth and Environmental Science at Lamont-Doherty Earth Observatory and will be blogging from Antarctica. He works with Professor Jonathan Kingslake on analyzing spatial and temporal trends of supraglacial lakes on the Antarctic Ice Sheet using satellite imagery.

Settling in to McMurdo

The Rosetta team has been in Antarctica for a week now and we’re almost done with unpacking and testing all of our equipment. Our first survey flight of the season is scheduled for the end of the week.

An official 'proof'! My photo by the McMurdo sign is proof that we have really made it here after a lot of anticipation!!

An official ‘proof’! My photo by the McMurdo sign is proof that we have really made it here after a lot of anticipation!!

The first few days of our time in Antarctica was spent on safety training and ‘waiting on the weather’. Each step of our set-up process, like receiving cargo, installing electricity in our tent, unpacking our boxes, and building disassembled instruments, needs to wait for safe weather conditions, which in Antarctica is by no means guaranteed. Our workstation is a yellow Jamesway tent on the airfield named Williams Field. It is about a thirty minute drive from McMurdo Station, on a nearby section of the Ross Ice Shelf.

The landscape seems endless with ice shelf merging into white cloudy skies. The airplanes on the ice are close to the only relief.

The landscape seems endless with ice shelf merging into white cloudy skies. The airplanes on the ice are close to the only relief.

Even though we are within a short drive of McMurdo station, a small town with most of the safety and logistical equipment on the entire continent, we still need to prepare ourselves for sudden, extreme weather. Every time we leave the relative safety of McMurdo, we carry our Extreme Cold Weather equipment and our tent has emergency food and sleeping equipment. Driving onto the ice shelf is a surreal experience: the landscape is a nearly featureless white, flat expanse, with only tiny buildings and the black, slug-like shapes of lounging seals to break up the uniform whiteness. When there are low-lying clouds, the ice and the sky seem to meld into a single white area.

Unpacking our workspace in the Jamesway that will be our 'command center' during our work here.

Unpacking our workspace in the Jamesway that will be our ‘command center’ during our work here.

After two days of unpacking, our little tent is becoming very cozy. We have a line of tables for our computers and printer, a coffee machine and two gas heaters, a number of powerful external hard drive units called a Field Data Management System. Our scientific instruments are coming together, as well. To keep both ourselves and our electronics warm, we keep two heat-stoves running all the time. In preparation for our flights, we’ve split into two shifts, one in the day and one at night. Myself and six other people spent last weekend transitioning our daily schedules to sleeping during the day and being awake to work over the night. Due to the polar latitude, the sun never goes down, so the two shifts experience nearly identical levels of light. Yet my sense of time is very confused and I often forget what day of the week I am currently in.

Setting up our basestations to support our flight data.

Setting up our basestations to support our flight data.

Before we start recording and processing data from our first survey flights, we need to rebuild the instruments that were deconstructed for shipping, and calibrate them to make sure the data recorded is accurate. With round-the-clock activity, we have set up everything in only a few days. One of the needed activities was hanging the gravimeter onto a freely-suspended gimbal with bungee cords so that it is stabilized against the movement of the plane. Many of the components of our sensors are very delicate, but a large number of the external components are larger, easily adjusted, and could be found in a hardware store. Unlike other fields of science, polar fieldwork operates best when adjustments can be made while wearing heavy gloves.

Helping Tej to calibrate the IcePod on the C130 aircraft.

Helping Tej to calibrate the IcePod on the C130 aircraft.

Additional set up involves installing “base stations” to record a background level of magnetics and GPS information. A five minute walk across the ice from our tent, we have erected two yellow tripods and partially buried a small box of sensors. The instruments are powered by a small solar panel that we set up nearby. Each tripod needed to be secured against wind by tying the legs to bamboo poles we buried in the snow, a snow anchor. The snow on the ice shelf is incredibly dry and compact, so digging into it feels like digging through styrofoam. Filling in the holes with snow, stamping on it, and waiting only a few minutes allows the snow to harden to a strength similar to concrete.

Checking on the data output inside the plane and hoping for good weather for a flight!

Checking on the data output inside the plane and hoping for good weather for a flight!

Our first test flight is scheduled for the end of the week. We will fly one of our survey lines and make sure that the instruments’ readings are accurate so that on future flights we will know that the instruments are working properly. In addition we will be ensuring that each of the instruments functions by checking sections of the data after every flight. My assigned role once flights are running regularly is to analyze the ice-penetrating radar during the night shift.

For more information about Rosetta-Ice, check out our website and the archive of this blog. Have questions about Rosetta-Ice or about living and working in Antarctica? Feel free to email your question to juliansantarctica@gmail.com, and I will try to answer it in the next blog entry!

Julian Spergel is a graduate student at the Department of Earth and Environmental Science at Lamont-Doherty Earth Observatory and will be blogging from Antarctica. He works with Professor Jonathan Kingslake on analyzing spatial and temporal trends of supraglacial lakes on the Antarctic Ice Sheet using satellite imagery.

What’s a few days delay when preparing to visit a 33 million year old ice sheet?

The Rosetta team has been delayed in Christchurch, NZ since October 20th, and today, the 24th, we are all hoping very hard that today will be the day, that the weather will cooperate and the plane will have no issues so that we can get to McMurdo and start preparing to work. Morale is still high, we have all enjoyed exploring the local sights in Christchurch in the spare time we suddenly have. But it would be a huge inconvenience if we stay in Christchurch too long.

The Dumont d'Urville base where winds have been recorded at 199 mph. (photo credit Samuel Blanc)

The Dumont d’Urville base where winds have been recorded at 199 mph. (photo credit Samuel Blanc)

The dangers of Antarctic air travel cannot be emphasized enough. The weather is notoriously temperamental: winds as fast as 199 mph (327km/h) have been recorded at Dumont D’Urville station. Wind gets funneled down mountains and through fjord valleys, picking up speed. Blowing snow can limit visibility in a matter of seconds. Even crossing the Antarctic Circle is dangerous. Because there are no large landmasses to break the 40th line of latitude, ocean and wind currents can spin unimpeded around the continent. This is called the Antarctic Circumpolar Current. Sailors called the latitudes between New Zealand and Antarctica in order of southernness the Roaring Forties, the Furious Fifties, and the Shrieking Sixties.

Yet this inaccessibility is two-sided. The spinning wall of wind and water acts as a thermal insulator and keeps Antarctica chilly. The extreme environment, the massive ice sheet, and the unique ecosystems that attract the scientific community are all due to this forbidding climate system.

Antarctica is an isolated massive block of land primarily covered in ice. (photo M. Turrin)

Antarctica is an isolated massive block of land primarily covered in ice. (photo M. Turrin)

Was Antarctica always so inhospitably cold? Surprisingly, no. The development of the Antarctic ice sheets are relatively recent compared to the 4.5 billion year old history of the Earth. The precise mechanism that triggered Antarctic glaciation is still debated, but there is significant evidence that continental scale glaciation began around 33 million years ago, at the boundary of the Eocene and Oligocene. A combination of lowering CO2 levels and the formation of the Circumpolar Current when South American and Antarctica detached led to mountain glaciers in the Trans-Antarctic mountains to expand until the continent was covered [10.1038/nature01290]. Prior to this point, Antarctica is believed to have been forested, and dinosaur and early mammal fossils have been found around the continent.

We theorize that the crustal depression that has become the embayment holding the Ross Ice Shelf developed during the break-up of Gondwana.

We theorize that the crustal depression that has become the embayment holding the Ross Ice Shelf developed during the break-up of Gondwana.

The glacial and geological history of the Ross Embayment, the bay in which the Ross Ice Shelf sits, is one of Rosetta-Ice’s leading research questions. By making measurements of the seafloor, we hope to improve our understanding of the timing and distribution of sea-floor extension in the geological past. The tectonics of the region are still not well understood. We theorize that the crustal depression that has become the embayment developed during the break-up of Gondwana, the Mesozoic supercontinent composed of modern-day South America, Africa, Australia, Antarctica, India, and Arabia around 200 million years ago. As it pulled apart over millions of years, it stretched the crust in the region of the Ross Sea, thinning and depressing it. Over the past 33 million years, glacial ice has carved out landforms that now lie under the ice. During our work, we will use our instruments to look through the ice shelf and map those present day landforms. We would like to improve our knowledge of the history of the region, both of the geology and of the ice shelf. Why is this important? In addition to increasing our knowledge of the world’s geological history, the past of the Ross Sea can give us clues to its future. If we see evidence that the Ross Ice Shelf has broken up or disappeared in the past, we can say that the present-day ice shelf has the capacity to disappear in the future.

Stay tuned for updates on our Antarctic arrival and our scientific work. We’re standing by in Christchurch, parkas on, bags in hand, excited and ready to start another season of Antarctic science.

Julian Spergel is a graduate student at the Department of Earth and Environmental Science at Lamont-Doherty Earth Observatory and will be blogging from Antarctica. He works with Prof. Jonathan Kingslake on analyzing spatial and temporal trends of supraglacial lakes on the Antarctic Ice Sheet using satellite imagery. He graduated with a BS in Geophysical Sciences with General Honors from the University of Chicago in 2016. He has been involved with a number of diverse projects and has been interested in polar studies since early in his career. His fieldwork has brought him north to the Svalbard Archipelago and south to McMurdo Station, Antarctica.

Learn more about previous years’ research, here.

For more on this project, please visit the project website: http://www.ldeo.columbia.edu/rosetta

Under the Sea Ice, Behold the Ancient Arctic Jellyfish

Arctic Sea Ice Ecology - Mon, 10/23/2017 - 14:20

The doings of creatures under the Arctic sea ice are many, but they are rarely observed by humans; it’s pretty hard to get under the ice to look. In recent years, marine biologist Andy Juhl and his colleagues have gotten around this problem by driving snowmobiles several miles from Point Barrow, Alaska, out onto the adjoining frozen Chukchi Sea, drilling holes in the four-foot-plus thick ice, and poking in a video camera attached to an small underwater vehicle.

Among the things that they have observed: sizable Chrysaora melanaster jellyfish floating by, trailing their foot-long-plus tentacles along the shallow bottom. Their presence came as a surprise: adult jellyfish, or medusae, are generally thought to live only a few months. Scientists had assumed that the species survived winter only in a life stage called polyps–formless masses that cling to rocks and release little baby medusae in the spring. In a scientific paper out this week, Juhl and colleagues say the videos indicate that the creatures in fact last through winter. They could even be several years old–the Methuselahs of medusae.

“One reason we were interested was, first of all, we saw them, and it was kind of weird,” said Juhl, a researcher at Columbia University’s Lamont-Doherty Earth Observatory. “The whole study is based on videos we made over several years.” Also, he says, the rich pollock fishery in the nearby Bering Sea is the engine for “everything fish”–fish sticks, fish paddies and other mystery-meat-type marine fast foods. But in some years, jellyfish numbers in the Bering Sea swell, and fishing nets can get seriously clogged–a problem that may crescendo over several years before dying back again. The study may reveal something about the jellyfish population dynamics that drive these cycles.

Juhl’s working hypothesis: cold winters, when sea ice is thick and long-lasting, are good for Chrysaora survival. He says the ice probably shields the medusae from turbulent winter storms, and the low water temperatures reduce their metabolism enough for them to subsist on relatively little food. “Life under sea ice is like living in a refrigerator–everything slows down,” he said. He said that jellyfish blooms may follow one or two years of heavy sea-ice cover because lots of adults survive.

Juhl points out that many other Arctic creatures also depend on sea ice. These range from lowly algae and bug-like amphipods that thrive on its underside to giant polar bears who roam around on top, waiting to pick off seals that emerge from breathing holes.

With Arctic climate warming and sea ice declining rapidly, what will happen to Chrysaora? Elsewhere in the world, including in the Mediterranean, other species of jellyfish are swarming and becoming pests, apparently in response to warmer waters, overfishing and coastal pollution. These forces are bad for other flora and fauna, but the resilient jellies often thrive, eventually taking over the ecosystem. In the far north, it could be the opposite; ice-loving jellies could decline if things warm up. So could the other, more iconic, creatures of the north that depend on sea ice. But at least jellyfish might not be clogging fishermen’s nets so much. “For most things, there are positives and negatives to climate change,” said Juhl.

One still unanswered question: Do these jellyfish sting? “I don’t know,” he said. “There aren’t that many people around there swimming to find out.”

Related: The Arctic’s Secret Garden

Final Stop – Antarctica’s Ross Ice Shelf

We have embarked! Our third Antarctic field season is underway putting us only 18 flights away from completing our mission to investigate the Ross Ice Shelf, the largest ice shelf in Antarctica. The Rosetta Ice Project is focused on developing a more complete understanding of the Ross Ice Shelf, the history of how it formed, what are the factors driving its current condition and what might control its future stability.

Drawing of the author Julian Spergel (by Freddy Bendekgey)

Drawing of the author Julian Spergel (by Freddy Bendekgey)

It is this writer’s first Antarctic field season, although traveling to Antarctica has been a life dream of mine since high school. I came to my obsession in an unusual way. In the summer of 2011, a heat wave knocked out the air conditioning units in my town. Sweltering, I took what little refuge there could be had in the public library. I had read somewhere that reading about cold places could cool you down, so for the next few weeks I pored over every account of polar exploration I could get my hands on. I was hooked, and especially hooked on Antarctica. It represented to me a place that remained mysterious and extreme, and whose challenging exploration by scientists represented the pinnacle of human ingenuity and international collaboration. I feel honored to be included in this field season, and to be documenting our findings and experiences for readers to learn from and enjoy. It is exhilarating to be on my way to achieving a personal goal of mine, though when I pictured myself as an Antarctic explorer as a teenager, I thought I would be taller!

An annotated version of the front of the Ross Ice Shelf from radar collected in this project. Note the shelf sits with most of the ice below the waterline.

An annotated radar image collected in the project showing the front of the Ross Ice Shelf. Note the shelf sits with most of the ice below the waterline.

To more thoroughly introduce the Rosetta-Ice project, it is a National Science Foundation funded multi-year collaboration between Lamont-Doherty Earth Observatory, Scripps Institute of Oceanography, Colorado College, and Earth & Space Research with critical support from the New York Air National Guard. Out goal is to complete a high-resolution survey of the Ross Ice Shelf in West Antarctica. The Ross Ice Shelf is a floating ice shelf roughly the size of Texas or of France that extends from the Trans-Antarctic Mountains into the Ross Sea, the portion of the Southern Ocean that faces New Zealand. Part of the ice shelf’s perimeter is grounded, at term that means frozen all the way down and connected at the base to the seafloor below. The rest of the shelf extends out floating as a thick apron of ice with about 10% of it visible above the ocean’s surface, the rest floating below the waterline. The ice shelf is up to 4000 thousand feet thick in its interior, and its margin with the sea is nine hundred feet thick in places. A large percentage of the surrounding ice streams in the Trans-Antarctic Mountains and West Antarctic Ice Sheet flow into the Ross Ice Shelf. As a result, the friction of the grounded portions affects the rate at which the ‘upstream’ ice flows and loses its mass through iceberg calving.

Lamont-Doherty Earth Observatory / Photo: Winnie Chu. The Rosetta project is focused on the Ross Ice Shelf in Antarctica. This shelf plays a critical role in stabilizing the Antarctic ice sheet, buttressing the ice that is constantly moving over the land surface. Studying how the ice, ocean and underlying land interact will inform us of potential change in the ice shelf from projected climate change. IcePod, shown along the front of the shelf, is a critical instrument in completing this project.

The IcePod flying over the the Ross Ice Shelf in Antarctica as part of the Rosetta project. The pod is lowered from an LC130 aircraft and holds a series of instruments that are critical to completing this project. (photo: Winnie Chu)

Rosetta-Ice is a detailed aerogeophysical survey, a series of survey flights collected using LC130s, rugged military cargo planes that fly equipment and support in the polar regions. The planes carries a variety of remote-sensing instrumentation inside an attached structure called IcePod, and flies a tight grid of observation tracts collecting data. The ultimate result will be a map of the Ross Ice Shelf with a spatial resolution of 10km (6mi). This will give us a comprehensive look into the ice shelf’s surface elevation, its internal glacial stratigraphy, its thickness, the ocean circulation beneath it, and the morphology of the bed beneath.

The research questions that the project seeks to answer concerns the ice shelf’s past and future. We want to understand how the ice shelf formed, and we are thus studying the internal structures within the ice and the bathymetry and geology of the bed underneath. Looking from the past to the future, we are interested in the stability of the floating ice. For this question, we are studying the circulation of ocean water underneath the ice, how the ocean interacts with the ice through melting, and where the ice shelf may be resting on the underlying bed. Each one of our instruments’ data gives us a piece of the answers. The Rosetta Stone, our project’s namesake, was inscribed with a message in multiple languages that could only be completely understood by comparing the three translations and interpreting them together. Likewise, we are interpreting our data from ice-penetrating radar, visual and infrared imagery, magnetic readings, and gravimeter information together to produce a complete picture of the Ross Ice Shelf’s dynamics.

McMurdo Base, Antarctica imaged with LiDAR. (processed by S. Starke)

McMurdo Base, Antarctica imaged with LiDAR. (processed by S. Starke)

In this coming week, we will be settling into McMurdo Station, the largest of Antarctica’s research stations, and setting up and calibrating our instruments so that we can begin this year’s flights as soon as we can. For more information about previous years’ work, please take a look at previous blog entries in the archives of this blog.

Author: Julian Spergel.  Julian will be blogging this season from Antarctica for the project.

For more on this project please go to the project website: http://www.ldeo.columbia.edu/res/pi/rosetta/

New Map of Alaska Seafloor Suggests High Tsunami Danger

Scientists probing under the seafloor off Alaska have mapped a geologic structure that they say signals potential for a major tsunami in an area that normally would be considered benign. They say the feature closely resembles one that produced the 2011 Tohoku tsunami off Japan, killing some 20,000 people and melting down three nuclear reactors. Such structures may lurk unrecognized in other areas of the world, say the scientists. The findings will be published tomorrow in the print edition of the journal Nature Geoscience.

The discovery “suggests this part of Alaska is particularly prone to tsunami generation,” said seismologist Anne Bécel of Columbia University’s Lamont-Doherty Earth Observatory, who led the study. “The possibility that such features are widespread is of global significance.” In addition to Alaska, she said, waves could hit more southerly North American coasts, Hawaii and other parts of the Pacific.

A tsunami can occur as ocean crust (brown area) dives under continental crust (orange), causing the ocean floor to suddenly moves. In one region off Alaska, researchers have found a large fault and other evidence indicating that the leading edge of the continental crust has split off, creating an area that can move more efficiently, and thus may be more tsunami-prone. (Anne Becel)

A tsunami can occur as ocean crust (brown area) dives under continental crust (orange), causing the ocean floor to suddenly move. In a region off Alaska, researchers have found a large fault and other evidence indicating that the leading edge of the continental crust has split off, creating a tsunami-prone area where the floor can move more efficiently. (Anne Becel)

Tsunamis can occur as giant plates of ocean crust dive under adjoining continental crust, a process called subduction. Some plates get stuck for decades or centuries and tension builds, until they suddenly slip by each other. This produces a big earthquake, and the ocean floor may jump up or down like a released spring. That motion transfers to the overlying water, creating a surface wave.

The 2011 Japan tsunami was a surprise, because it came partly on a “creeping” segment of seafloor, where the plates move steadily, releasing tension in frequent small quakes that should prevent a big one from building. But researchers are now recognizing it may not always work that way. Off Japan, part of the leading edge of the overriding continental plate had become somewhat detached from the main mass. When a relatively modest quake dislodged this detached wedge, it jumped, unleashing a wave that topped 130 feet in places. The telltale sign of danger, in retrospect: a fault in the seafloor that demarcated the detached section’s boundary landward of the “trench,” the zone where the two plates initially meet. The fault had been known to exist, but no one had understood what it meant.

The discovery was made near the end of the Alaska Peninsula. A tsunami from here could reach many land areas across the Pacific. (Anne Becel)

The discovery was made around the western end of the Alaska Peninsula and the eastern Aleutian Islands. (Anne Becel)

The researchers in the new study have now mapped a similar system in the Shumagin Gap, a creeping subduction zone near the end of the Alaska Peninsula some 600 miles from Anchorage. The segment is part of a subduction arc spanning the peninsula and the Aleutian Islands. Sailing on a specially equipped research vessel, the scientists used relatively new technology to penetrate deep into the seafloor with powerful sound pulses. By reading the echoes, they created CAT-scan-like maps of both the surface and what is underneath. The newly mapped fault lies between the trench and the coast, stretching perhaps 90 miles underwater more or less parallel to land. On the seafloor, it is marked by scarps about 15 feet high, indicating that the floor has dropped one side and risen on the other. The fault extends down more than 20 miles, all the way to where the two plates are moving against each other.

The team also dropped seismometers to the ocean floor. These revealed many small quakes typical of creeping plates originating in the area landward of the fault, but fewer on the seaward side. This suggests that while the deeper part of the subduction zone is indeed creeping along harmlessly, the outer, shallower parts are stuck against each other, and getting stretched. This may have created the fault, slowly tearing the region off the main mass; or the fault may be the remains of a past sudden movement. Either way, it signals danger, said coauthor Donna Shillington, a Lamont-Doherty seismologist.

Seafloor images were collected aboard the research vessel Marcus G. Langseth, the nation's main ship for seismic research. (Anne Becel)

Seafloor images were collected aboard the research vessel Marcus G. Langseth, the nation’s main ship for seismic research. (Courtesy Lamont-Doherty Earth Observatory)

“With that big fault there, that outer part of the plate could move independently and make a tsunami a lot more effective,” said Shillington. “You get a lot more vertical motion if the part that moves is close to the seafloor surface.” A rough analogy: imagine snapping off a small piece of a dinner plate, laying the two pieces together on a table and pounding the table from below; the smaller piece will probably jump higher than if the plate were whole, because there is less holding it down.

Other parts of the Aleutian subduction zone are already known to be dangerous. A 1946 quake and tsunami originating further west killed more than 160 people, most in Hawaii. In 1964, an offshore quake killed around 140 people with landslides and tsunamis, mainly in Alaska; 19 people died in Oregon and California, and waves were detected as far off as Papua New Guinea and even Antarctica. In July 2017, an offshore quake near the western tip of the Aleutians triggered a Pacific-wide tsunami warning, but luckily it produced just a six-inch local wave.

As for the Shumagin Gap, in 1788, Russian colonists then living on nearby Unga Island recorded a great quake and tsunami that wiped out coastal structures and killed many native Aleut people. The researchers say it may have originated at the Shumagin Gap, but there is no way to be sure. Rob Witter, a geologist with the U.S. Geological Survey (USGS), has scoured area coastlines for evidence of such a tsunami, but so far evidence has eluded him, he said. The potential danger “remains a puzzle here,” he said. “We know so little about the hazards of subduction zones. Every little bit of new information we can glean about how they work is valuable, including the findings in this new paper.”

In rural Alaska, infrastructure tends to cluster along the coast, making it vulnerable to tsunami. Waves generated here could reach to Hawaii and beyond. (Anne Becel)

In rural Alaska, infrastructure tends to cluster along the coast, making it vulnerable to tsunami. Here, a community on Kodiak Island. Waves generated in this region could reach to Hawaii and beyond. (Matthias Delescluse)

The authors say that apart from Japan, such a fault structure has been well documented only off Russia’s Kuril Islands, east of the Aleutians. But, Shillington said, “We don’t have images from many places. If we were to look around the world, we would probably see a lot more.” John Miller, a retired USGS scientist who has studied the Aleutians, said that his own work suggests other segments of the arc have other threatening features that resemble both those in the Shumagin and off Japan. “The dangers of areas like these are just now being widely recognized,” he said.

Lamont seismologists have been studying earthquakes in the Aleutians since the 1960s, but early studies were conducted mainly on land. In the 1980s, the USGS collected the same type of data used in the new study, but seismic equipment now able to produce far more detailed images deep under the sea floor made this latest discovery possible, said Bécel. She and others conducted the imaging survey aboard the Marcus G. Langseth, the United States’ flagship vessel for acoustic research. Owned by the U.S. National Science Foundation, it is operated by Lamont-Doherty on behalf the nation’s universities and other research institutions.

The other coauthors of the study are Spahr Webb, Mladen Nedimovic and Jiyao Li of Lamont-Doherty; Matthias Delecluse and Pierre-Henri Roche of France’s PSL Research University; Geoffrey Abers and Katie Keranen of Cornell University; Demian Saffer of Penn State; and Harold Kuehn of Canada’s Dalhousie University.

RELATED: Ancient Faults and Water Are Sparking Earthquakes Off Alaska

 

Eavesdropping on the Ocean’s Mighty Microorganisms

Mesoscope Hawaiian Islands - Thu, 07/13/2017 - 11:05

By Gwenn M. M. Hennon

Gwenn Hennon demonstrates experiment aboard the RV Kilo Moana

Gwenn Hennon demonstrates experiment aboard the RV Kilo Moana

The microscopic organisms that make up ocean ecosystems are invisible to the naked–eye, yet they are responsible for producing half the oxygen we breathe, and for sustaining all the world’s fisheries. Now, nearing the end of our three-week cruise of the North Pacific off Hawaii, we are working to understand how these tiny bacteria connect and communicate with one another.

We know bacteria have the ability to sense and respond to an unknown number of chemical signals, but we think it may be tens to hundreds. A few signals we know from lab experiments include quorum sensing molecules. Quorum sensing molecules are released by other bacteria to change the way cells behave when they have reached a sufficient density, or quorum. We know from previous work in the Dyhrman lab and the Van Mooy lab that quorum signaling is important in the bacteria communities that surround a particularly large and important
cyanobacterium, Trichodesmium. Tricho, as it is affectionately referred to, fixes large quantities of nitrogen fertilizer directly from nitrogen gas ( see my post: http://bit.ly/2udAf6F ). The bacteria surrounding Tricho, or its microbiome can greatly affect the rates of nitrogen fixation in ways we do not yet fully understand. Nitrogen fixation is one of the most important biochemical processes on earth and in the oceans. In ocean ecosystems, it enables microorganisms to grow even when other nutrients, such as nitrate and ammonium, are scarce.

We would like to understand which bacteria are actively recruited to colonize Tricho and other large cells, and how chemical signaling impacts this process. To do this, we created a trap for bacteria using new techniques pioneered by our collaborator Otto Cordero. From scratch, we made microscopic beads embedded with phytoplankton cell extract and magnetic particles that allow us to pull the beads out of solution, separating them from the seawater and free-living cells. Inside the bottle I’m holding (see photo) are thousands of these tiny beads mixed with ocean bacteria. Over the past few weeks, we have mixed natural bacteria found in the surface ocean with different mixtures of chemical signals and phytoplankton-flavored beads. After we take our samples back to the lab, we can use DNA sequencing as a kind of universal barcode to identify the bacteria caught in our trap.

I can’t wait to see what we will discover from these experiments, which give us new tools to eavesdrop on the conversation among marine bacteria. Understanding how bacteria communicate through signals is an important challenge for predicting the future of the ocean’s complex microbial ecosystem.

Deep thoughts from the Deep Blue Sea

Mesoscope Hawaiian Islands - Thu, 07/06/2017 - 11:36

By Gwenn M. M. Hennon

Post Doc Researcher Gwenn Hennon and colleagues pulling samples from the depths of the North Pacific

Gwenn Hennon and colleagues pulling samples from the depths of the North Pacific

As far as I can see from the ship to the horizon there is nothing but deep blue sea. Not a single ship has passed within sight since we left the north shore of Oahu. We are only a day’s steam away from the
Hawaiian Islands, yet in the vast Pacific Ocean we could go weeks without seeing another ship. The ship is nothing more than a tiny speck on a massive blue marble. This is one of the dwindling places on
earth where I feel truly alone with my thoughts.

The sea is a deep blue, so clear, that you might think it was devoid of life. We have seen only a few seabirds circling the ship and playing in the air currents we generate. We haven’t seen any whales or
sharks, only an occasional flying fish taking to the air in front of our bow wake. In this apparent desert, microbial life is king. Microbes here can persist off of little more than sunlight and gasses in the air. Marine microbes are expert recyclers, rapidly scavenging the precious little nitrogen and phosphorous fertilizers in the
surface ocean. Some of these microbes can even take nitrogen directly
from the air to use as fertilizer. Chemists figured out how to make
fertilizer from nitrogen gas by using incredible heat and pressure,
but these microbes can do it at ambient temperature and pressure.
Billions of years of evolution has given these tiny cells better
technology than the accumulated efforts of every chemist in the
history of humanity (I note with more than a little envy as a
chemistry major).

Very little gets wasted in this hyper-efficient ecosystem, but a
little waste is inevitable. Some of these microbes die, killed by
viruses or damaged by UV rays. Instead of being recycled or passed up
the food chain a tiny fraction of them will sink into the deep. A slow
rain of this waste falls from the surface ocean into the perpetually
dark “twilight zone” of ocean. Carried down with this waste is carbon,
nitrogen and phosphorous from the surface. At depth, these elements
are released by yet more microbes, munching away on the pieces of the
dead and dying cells. About three miles directly below us on the sea
floor a very small fraction of this waste will be buried in sediments
and preserved for millions of years. In the enormous warehouse of
sediment cores drilled from the ocean floor in Lamont-Doherty Earth
Observatory, I have seen first-hand how the remains of ancient
microbes allow researchers to look into the deep past.

In the next few days, the MESOSCOPE team will set traps to collect
freshly sinking material. Our estimates of how much carbon and other
elements sink out of the surface ocean every year are still very
uncertain. We do not yet understand the factors that allow particles
to sink out and escape the gauntlet of scavengers. Carbon carried to
depths by dead microbes is estimated to be on the same order of
magnitude as the yearly global emissions from fossil fuel burning. So
far, the ocean has absorbed about half of the carbon dioxide emitted
into the atmosphere from human activity, but we can’t yet predict how
the equation might change in the future.

Standing on the back deck of the Kilo Moana, the deep blue sea makes
me feel both insignificantly small and reminds me of the power of
microbial life to shape our planet. In a million years how many atoms
of carbon from my exhaled breath or from the smoke stack of the Kilo
Moana will be trapped in deep sea sediments? Not sure I could
calculate that yet… but give me some time.

Setting Off to Explore the Depths

Mesoscope Hawaiian Islands - Thu, 06/29/2017 - 10:47

By Gwenn Hennon and Matthew Harke

Loading the R/V Kilo Moana

Loading the R/V Kilo Moana

For the past few days, we have been loading the gear and setting up our lab on the R/V Kilo Moana. We have to secure everything down to the benches to prevent equipment from falling and being damaged in rough seas.

Yesterday, we set sail at 8am, rounded the Island of O’ahu, and headed north into the blue waters of the North Pacific Subtropical Gyre. We are currently in transit, but this gives us time to test equipment and make sure everything is in order by the time we reach our first station. It also gives us time to help with the many shipboard operations. After a hearty breakfast of eggs, bacon, tater tots, and coffee, we had the opportunity to help deploy a “towfish” from a boom extending out 15 meters off the starboard side of the boat. Since this was the first deployment of its kind on this vessel, there were a lot of hands to help. Matt is the guy in the blue hard hat.

A towfish is a device which looks like a torpedo. The towfish is tethered to the boat and lowered into the water with the boom. It then “swims” through the water while the ship is under way, allowing us to take continuous samples. The team is trying to collect trace metal samples, and so they attached a trace metal-clean hose to the towfish to pump water as far from the ship as possible.

towfishOne difficulty with working on a large steel ship is that it “leaks” a lot of iron (as well as other metals) into the water. If you care about measuring iron levels in the water, you need to find a way to get away from the ship, and this method seems to do the trick. After a successful deployment and refueling at lunch, we also helped deploy and recover an underway CTD off the stern of the vessel. CTD stands for conductivity, temperature, and depth. This device allows us to profile the eddy as we transit across, giving us an in-depth look at the physical structure of the eddy. This will allow us to more accurately target water features when we stop to collect water later on. Each deployment lasts around 15 minutes and involves dropping the underway CTD off the back of the boat, letting it sink to 300 meters, reeling it in, resetting it, and then redeploying it. All of this is done while the ship is moving at about 8 knots. This will go on for the next day or so, as it takes a few days to traverse an eddy.

Racing time to Explore Ocean Ecosystems: A Mother’s Work

Mesoscope Hawaiian Islands - Thu, 06/22/2017 - 11:42

By Gwenn Hennon, PhD

Gwen HennonAs I kissed my 1-year-old son goodbye this morning at daycare it seemed like any other day. Yet as I dropped him off, I knew that I wouldn’t see him again for almost four weeks. I will be returning just in time for his second birthday. My heart aches knowing that he will likely be calling for me as my husband gets him ready for bed tonight, not understanding why I can’t be there to read him a story and kiss him goodnight.

Don’t get me wrong, I love my job! I love that as a biological oceanographer I get to go to sea off the Hawaiian Islands to study how ocean life is shaped by swirling 60-mile-wide currents. The microscopic organisms that make up ocean ecosystems are invisible to the naked-eye, yet they are responsible for producing half the oxygen we breathe and sustaining all the world’s fisheries.

Scientists like myself are in a race against time to understand the fundamental drivers of ocean ecosystems before climate change pushes them towards a new unknown state. State-of-the-art models predict that warming, ocean acidification, and changes in ocean currents predicted for the year 2100 will have big impacts on the structure of the microbial ecosystem. These changes have large potential consequences for carbon sequestration and the rate of climate change, as well as the security of the world’s food supply. 2100 may seem like a long time off, but it’s likely that my son will be alive to see it. When he is 85 years old, what will he make of the world we have left for him? Did we accurately predict changes to the ocean ecosystem? Did we do enough to avert an ecological disaster?

Because no one has invented a time machine, we have to make do with our current best guesses. Unfortunately, our picture of the ocean ecosystem is far from complete, making it difficult to predict the future.  As I board my flight for Honolulu, I’m grateful for the opportunity to fit a few more puzzle pieces into the big picture of how the ocean ecosystem functions. Every scientist and crew member participating in this research cruise will make sacrifices, leaving behind family and friends, and working round the clock in an effort to gather new data to understand ocean processes. Wish us luck for a successful trip!

Could Climate Change Shut Down the Gulf Stream?

Greenland Thaw: Measuring Change - Tue, 06/06/2017 - 13:28
The Gulf Stream

The Gulf Stream

The 2004 disaster movie “The Day After Tomorrow” depicted the cataclysmic effects—superstorms, tornadoes and deep freezes— resulting from the impacts of climate change. In the movie, global warming had accelerated the melting of polar ice, which disrupted circulation in the North Atlantic Ocean, triggering violent changes in the weather. Scientists pooh-poohed the dire scenarios in the movie, but affirmed that climate change could indeed affect ocean circulation—could it shut down the Gulf Stream?

The many ocean currents and wind systems that move heat from the equator northwards towards the poles then transport the cold water back towards the equator make up the thermohaline circulation. (Thermo refers to temperature while haline denotes salt content; both factors determine the density of ocean waters.) It is also called the Great Ocean Conveyor, a term coined in 1987 by Wallace Broecker, Newberry Professor of Geology in the Department of Earth and Environmental Sciences at Columbia University and a scientist at Lamont-Doherty Earth Observatory. Broecker theorized that changes in the thermohaline circulation triggered dramatic changes in the North Atlantic during the last ice age.

Thermohaline_Circulation_2

In the high latitudes, the cold water on the surface of the ocean gets saltier as some water evaporates and/or salt is ejected in the forming of sea ice. Because saltier colder water is denser and thus heavier, it drops deep into the ocean and moves along the depths until it can rise to the surface near the equator, usually in the Pacific and Indian Oceans. Heat from the sun then warms the cold water at the surface, and evaporation leaves the water saltier. The warm salty water is then carried northwards; it joins the Gulf Stream, a large powerful ocean current that is also driven by winds. The warm salty water travels up the U.S. east coast, then crosses into the North Atlantic region where it releases heat and warms Western Europe. Once the water releases its heat and reaches the North Atlantic, it becomes very cold and dense again, and sinks to the deep ocean. The cycle continues. The thermohaline circulation plays a key role in determining the climate of different regions of the earth.

The Atlantic Meridional Overturning Circulation, part of the thermohaline circulation which includes the Gulf Stream, is the ocean circulation system that carries heat north from the tropics and Southern Hemisphere until it loses it in the northern North Atlantic, Nordic and Labrador Seas, which leads to the deep sinking of the colder waters.

Greenland melting in 2012

Greenland melting in 2012

Because the thermohaline circulation is mainly driven by differences in the water’s density, it depends upon the cold dense waters that sink into the deep oceans. Global warming can affect this by warming surface waters and melting ice that adds fresh water to the circulation, making the waters less saline; this freshening of the water can prevent the cold waters from sinking and thus alter ocean currents.

As the planet warms, more and more fresh water is entering the system. In 2016, the extent of Greenland’s melting sea ice set a new record low. That May, the Arctic lost about 23,600 square miles of ice daily, compared to the long-term average loss of 18,000 square miles per day. A study by Marco Tedesco, a research professor at Lamont-Doherty specializing in Greenland, and colleagues suggested that a reduction in the temperature difference between the polar and temperate regions (the Arctic is warming twice as fast as the rest of the planet) pulled the jet stream air currents northwards. The warm moist air it carried hovered over Greenland, causing the record melting.

So far this year, Tedesco said, “The melting in Greenland is within the mean, but it’s still above the average of what was happening 20 years ago…The snow melt from Siberia has also been melting sooner, there’s been more fresh water from Greenland, there’s more fresh water from sea ice in the Arctic Ocean and more fresh water from North Canada which has been melting at an increasing rate. All these factors are pointing in the direction of increasing the freshwater discharge in the North Atlantic section of the Arctic. It’s very likely going to have an impact.”

Greenland's ice cap is darkening

Greenland’s ice cap is darkening

In addition to warming temperatures accelerating Greenland’s melting, the snow and ice are being darkened by black carbon,  (reducing their reflectivity and warming the snow), and wind-blown algae and bacteria that are growing in holes in the ice. “More biological activity implies darker surfaces which in turn implies more melting,” said Tedesco. “But I think there is still not enough knowledge to properly project [what the impacts could be]…We know there is an impact and it’s important to quantify that impact because we need to know what the processes that we need to consider are to do proper projections.”

A 2015 study hypothesized that fresh water, which increased in the northern Atlantic by more than 4,500 cubic miles (19,000 km3) between 1961 and 1995, weakened the deep water formation of the Atlantic Meridional Overturning Circulation, particularly after 1975. The circulation has slowed between 15 and 20 percent in the 20th century, an anomaly unprecedented over the last millennium, which suggests it is not due to natural variability. The scientists hypothesized that this could explain why, in 2014, a specific patch in the middle of the North Atlantic was the coldest on record since 1880 while global temperatures everywhere else were increasing. The study suggested that the unusual cooling of this region could be due to a weakening of the global conveyor that is already occurring. (It seems to have made a partial recovery since 1990.)

Michael Mann, Distinguished Professor of Atmospheric Science at Penn State University, one of the study’s authors, noted that if the Atlantic Meridional Overturning Circulation were to totally collapse over the next few decades, it would change ocean circulation patterns, influence the food chain, and negatively impact fish populations. We would not return to very cold conditions, however, because the oceans have taken up so much heat.

Another 2015 study that modeled a hypothetical slowdown or collapse of the Atlantic Meridional Overturning Circulation concluded that a collapse could result in widespread cooling throughout the North Atlantic and Europe (though this would be somewhat mitigated by global warming), increased sea ice in the North Atlantic, changes in tropical precipitation patterns, stronger North Atlantic storms, reduced precipitation and river flow as well as reduced crop productivity in Europe. These effects would impact many regions around the globe.

Sea levels are rising at Assateague

Sea levels are rising fast at Assateague in MD and VA.

Sea levels would be affected as well. Currently sea levels are lower on the U.S. east coast because waters east of the Gulf Stream, closer to Europe, are warmer and expand, so sea levels there are higher. If the Gulf Stream is weakened, the temperature differential between the two sides is reduced, so sea levels will rise on the west of the Gulf Stream along the U.S. east coast and the North Atlantic. In fact, sea levels along the coast and the Gulf of Mexico are rising faster than in any other part of the U.S, and some data suggests that it is because the Gulf Stream has already begun to slow down. Other research attributed a jump in sea level rise from New York to Newfoundland from 2009 to 2010 to the Atlantic Meridional Overturning Circulation slowing down 30 percent in the same period, as well as unusual wind currents that pushed ocean waters towards the coast.

Not all scientists agree that the Atlantic Meridional Overturning Circulation is slowing or that if it is, the phenomenon is caused by human induced global warming. A 2016 study suggested that while a great deal of fresh water has been discharged from Greenland, it’s difficult to track what happens to it because of eddies and currents. This research concluded that most of Greenland’s meltwater moves southward, and what remains of the fresh water is not enough to affect the Atlantic Meridional Overturning Circulation. The scientists did acknowledge, however, that the ongoing rapid melting of Greenland and increases of fresh water could eventually affect it.

The bottom line is that the thermohaline circulation is a very complex system and scientists do not yet understand all the variables involved in how it functions. There is an ongoing debate about why the Atlantic Meridional Overturning Circulation has weakened and how much is due to the effects of human activity on the climate.

Earth during the Ice Age

Earth during the Ice Age

In the Earth’s past, scientists have seen evidence of large inputs of fresh water into the North Atlantic from melting glaciers and ice caps as well as changes in the thermohaline circulation during transitions in and out of glacial periods. Global warming could potentially cause a thermohaline circulation shutdown and subsequent regional cooling, but because Earth will continue to warm as a result of greenhouse gas emissions, it would not produce another Ice Age. If the thermohaline circulation shut down, cooling would likely occur only in regions that are currently warmed by the ocean conveyor. And even if the thermohaline circulation did shut down, winds would still likely drive the Gulf Stream; however, there would be less warm water from the tropics and the Gulf Stream could become cooler and not reach as far north.

The 5th assessment report of the Intergovernmental Panel on Climate Change says, “…the Atlantic Meridional Overturning Circulation is generally projected to weaken over the next century in response to increase in atmospheric greenhouse gas emissions…. Overall, it is likely that there will be some decline in the AMOC by 2050, but decades during which the AMOC increases are also to be expected.”

According to Broecker, although reorganizations of ocean circulation are at the core of what happened in the past, we cannot say what the likelihood is that warming due to greenhouse gases will trigger yet another large and abrupt change. But if it were to occur, the consequences would be far less severe since, in the past, large existing expanses of sea ice were significant players in cooling the planet. “A conveyor shutdown is not likely,” said Broecker. “But if it happened, it would be ten times less dramatic and important than what happened during the glacial period when it caused a 10˚C temperature change.”

“We are monitoring the strength of deep water going south,” he said. “And we are finding large seasonal changes and interannual changes…It’s a complicated system and we can’t make any predictions.”

“The important thing is to understand better what is happening, by when it’s happening and what the potential implications will be,” said Tedesco. “Our priority is to better estimate the behavior of the Arctic and its connections to the temperate part of the planet in the short and long term…The question is not if things are going to change, the thing is how fast and when are they going to change, and what are the changes we’re going to see. There are changes at the local scale that are occurring on a much shorter time frame, and changes in the long-term that could include the shutdown of the ocean circulation. We need to understand the processes to properly build the models [to make projections].”

Lamont-Doherty’s Arctic Switchyard Project explores the circulation, variability, and driving mechanisms of the fresh water arriving in the Arctic Ocean, north of the eastern Canadian Archipelago and Greenland.

 

Sampling on the Ganges and Brahmaputra Rivers

Geohazards in Bangladesh - Sat, 02/04/2017 - 21:51
Chris smiling broadly as he and Humayun buy 11 lbs of Jordibaja, a local Kushtia snack food from the most famous bakery that makes it.

Chris smiling broadly as he and Humayun buy 11 lbs of Jordibaja, a local Kushtia snack food from the most famous bakery that makes it.

From Khulna in the SW, we are heading to Rajshahi on the Ganges River, but first we are stopping at Kushtia, Humayun’s home town. Because the road on the more direct route is supposed to have bad road conditions, we took a longer route, way longer. It wiped out any chance to get to Rajshahi in time for some fieldwork, but it did my districts (states) of Bangladesh visited to 40 out of 64. After many hours on the road, we reached Kushtia and out goal – jordibaja, a fried noodle snack that is only available here. Chris bought ten 500 gram bags, about 11 lbs, at the bakery that makes

Liz in Rajshahi walking back to our group protected by two policewoman that were part of our escort during a quick visit back to our van.

Liz in Rajshahi walking back to our group protected by two policewoman that were part of our escort during a quick visit back to our van.

the best, of course. We then had a late lunch and continued to Rajshahi where we were once again joined by a police escort. Different teams stayed with us until we left the area. After finding our hotel, we all had our first hot water shower since we left Dhaka. Living on boats is great, except for the complete lack of hot water. Once cleaned up, we went to Humayun’s sister for a delicious dinner. After dinner, the commissioner of police, a former student of Humayun’s stopped by. He suggested we visit some of the chars (sandy river islands) close to Rajshahi rather than the places we went

Our police escort watches Chris and Dan measuring spectra on a char (sandy river island) to compare with satellite measurements.

Our police escort watches Chris and Dan measuring spectra on a char (sandy river island) to compare with satellite measurements.

to other years, an hour or more drive away. Chris and Dan checked their satellite images and found that the nearby chars would work, probably dsaving 2-3 hrs of driving.

The next morning, we headed off with out new escort, that included two policewoman. However, that had to switch off when we crossed from one precinct to another. Renting a country boat we crossed the Ganges to the chars. While Dan and Chris (with Humayun) made salinity, moisture and spectroscopic measurements, Liz and I

Dan measures the water content of a small area of quicksand we found while Liz is being sucked in as she explores it.

Dan measures the water content of a small area of quicksand we found while Liz is being sucked in as she explores it.

scouted for the proper sediment samples for her OSL needs. After wandering about the island we found what she wanted and collected a sample. Until now, her studies of the delta did not have any samples from the Ganges itself. For Dan and Chris to get the observations they wanted, we visited several chars before ending up back at the first one for them to study the transition from sandy sediments to rice fields. As soon as the chars have deposits of the right kind of sediments, people start planting crops. If the char continues

Digging out our OSL dating sample of silt on the Ganges. The tape wrapped PVC pipe had been hammered entirely into the outcrop. The sample inside must not be exposed to light or it will be ruined.

Digging out our OSL dating sample of silt on the Ganges. The tape wrapped PVC pipe had been hammered entirely into the outcrop. The sample inside must not be exposed to light or it will be ruined.

to grow and stabilize, they will move there as well. They are great places to live 9 months of the year, but a struggle during the high water of the monsoon season. The islands with migrate, eroding from one side while sediment deposits on the other. The char people have to move frequently as the chars move out from under their homes. Liz and I wandered off and found another place to sample. Now she have both a sand and a silt samples from the Ganges. It only took a few hours to accomplish the more specific tasks of this field program. When we first started visiting chars 12 years ago, we explored then from the morning

Chris and Dan discussing notes on locations to visit based on recent satellite images and entering them into the GPS.

Chris and Dan discussing notes on locations to visit based on recent satellite images and entering them into the GPS.

until dusk. We needed to see and explore all aspects of this new environment for us. Now, we are building on our work with much more focused activities.

Off the river by early afternoon, we drove across country to Bogra near the Jamuna River, as this part of the Brahmaputra is known. We were able to arrive around sunset, avoiding the sometimes frightening driving in the dark. For old times sake, we skipped the new hotel that was booked and stayed at the colorful Parjartan Hotel that we first used

Chris, Dan, and Bulbul, our driver, walking down the embankment at Sirajganj. During the summer, the water level will reach the top of the embankment as the river flow increases by a factor of 10 or more.

Chris, Dan, and Bulbul, our driver, walking down the embankment at Sirajganj. During the summer, the water level will reach the top of the embankment as the river flow increases by a factor of 10 or more.

in 2005. It is literally painted the colors of the rainbow, as well as having more character, even if everything is not quite working. This was the hotel where my room once had electric outlets of 4 different shapes, requiring every adapter I had to recharge my equipment. Now I always bring an outlet strip so I only need one adapter.

We had planned to go north to Gaibandha, but a new satellite overpass showed that we could get all the data we needed farther south at Sirajganj. We could cut out a day. As it turns out, this was fortuitious. I have a family

Humayun walks to the country boat we rented at Sirajganj to bring us across the river to the chars.

Humayun walks to the country boat we rented at Sirajganj to bring us across the river to the chars.

emergency and have to return to the U.S. From Sirajganj we could return to Dhaka, rather than stay at Tangail. Chris and the others can do the rest of the field work as day trips from Dhaka. It is more driving for them, but will enable be to catch the evening flight back to the U.S. We packed up and headed to the embankment at Sirajganj, which protects the city from the shifts in the Jamuna River. We walked down the embankment (the river level is about 7 m or 23 feet higher during the summer monsoon season). We headed for a large char that

Liz examines an outcrop on the large char across from Sirajganj while looking for appropriate sediments to sample. Wherever the conditions are right, the chars are planted with crops while the bare sand remains exposed in the younger parts of the char.

Liz examines an outcrop on the large char across from Sirajganj while looking for appropriate sediments to sample. Wherever the conditions are right, the chars are planted with crops while the bare sand remains exposed in the younger parts of the char.

we first visited in 2005. It has grown and become attached to other chars. It also has much more agriculture, they are growing rice, peanuts, lentils, corn and more. The complex history of changes in the char provides lots of different sediment types for Chris and Dan and plent of cut bank surfaces for Liz to get a good silt sample. A few hours of exploring, sampling, measuring and we were done. Since it is Friday, the Muslim holy day and the weekend here, traffic is light until we reach Dhaka. Near the university and our hotel, the streets are packed with people and rickshaws. Still we manage to get to the university to drop off equipment and for me to get 7

Liz measures the position of the hammered in sampling tube before we dig out and collect our last sample, a silt from the Jamuna (Brahmaputra) River.

Liz measures the position of the hammered in sampling tube before we dig out and collect our last sample, a silt from the Jamuna (Brahmaputra) River.

GPS receivers that finally have to be returned to UNAVCO after 10 years. This is the last of the 11 we were lent in 2007 by them. They provide geodetic data and services for NSF and allowed us multiple extensions that enabled us to get this much needed data for so long. It is the basis for our paper on the potential earthquake hazard in Bangladesh as we can see the slow motion of the surface (0-17 mm/y) that indicates the buildup of strain in the earth. Then back to our hotel to meet Dhiman and have a final dinner together before an Uber takes me to the airport. It is sad to leave early, but I

A local farmer shows Liz the peanuts he is growing on the char (behind them). Peanuts and lentils are common winter, or rabi, crops on the higher, drier parts of the char. The freshest peanuts we ever ate.

A local farmer shows Liz the peanuts he is growing on the char (behind them). Peanuts and lentils are common winter, or rabi, crops on the higher, drier parts of the char. The freshest peanuts we ever ate.

am needed at home and they can carry on without me for the last few days. They will visit the confluence of the Ganges and Brahmaputra Rivers, and the Padma, as the combined river is called. For me, my critical goals for this trip were accomplished.

Microbial community segmentation with R

Chasing Microbes in Antarctica - Thu, 02/02/2017 - 18:39

In my previous post I discussed our recent paper in ISME J, in which we used community structure and flow cytometry data to predict bacterial production.  The insinuation is that if you know community structure, and have the right measure of physiology, you can make a decent prediction of any microbial ecosystem function.  The challenge is that community structure data, which often has hundreds or thousands of dimensions (taxa, OTUs, etc.), is not easily used in straightforward statistical models.   Our workaround is to reduce the community structure data from many dimensions to a single categorical variable represented by a number.  We call this process segmentation.

You could carry out this dimension reduction with pretty much any clustering algorithm; you’re simply grouping samples with like community structure characteristics on the assumption that like communities will have similar ecosystem functions.  We  use the emergent self organizing map (ESOM), a neural network algorithm, because it allows new data to be classified into an existing ESOM.  For example, imagine that you are collecting a continuous time series of microbial community structure data.  You build an ESOM to segment your first few years of data, subsequent samples can be quickly classified into the existing model.  Thus the taxonomic structure, physiological, and ecological characteristics of the segments are stable over time.  There are other benefits to use an ESOM.  One is that with many samples (far more than we had in our study), the ESOM is capable of resolving patterns that many other clustering techniques cannot.

There are many ways to construct an ESOM.  I haven’t tried a Python-based approach, although I’m keen to explore those methods.  For the ISME J paper I used the Kohonen package in R, which has a nice publication that describes some applications and is otherwise reasonably well documented.  To follow this tutorial you can download our abundance table here.  Much of the inspiration, and some of the code for this analysis, follows the (retail) customer segmentation example given here.

For this tutorial you can download a table of the closest estimated genomes and closest completed genomes (analogous to an abundance table) here.  Assuming you’ve downloaded the data into your working directory, fire up Kohonen and build the ESOM.

## Kohonen needs a numeric matrix edge.norm <- as.matrix(read.csv('community_structure.csv', row.names = 1)) ## Load the library library('kohonen') ## Define a grid. The bigger the better, but you want many fewer units in the grid ## than samples. 1:5 is a good ballpark, here we are minimal. som.grid <- somgrid(xdim = 5, ydim=5, topo="hexagonal") ## Now build the ESOM! It is worth playing with the parameters, though in ## most cases you will want the circular neighborhood and toroidal map structure. som.model.edges <- som(edge.norm,                  grid = som.grid,                  rlen = 100,                  alpha = c(0.05,0.01),                  keep.data = TRUE,                  n.hood = "circular",                  toroidal = T)

Congratulations!  You’ve just constructed your first ESOM.  Pretty easy.  You’ve effectively clustered the samples into the 25 units that define the ESOM.  You can visualize this as such:

plot(som.model.edges, type = 'mapping', pch = 19)

There are the 25 map units, with the toroid split and flattened into 2D.  Each point is a sample (row in the abundance table), positioned in the unit that best reflects its community structure.  I’m not going to go into any depth on the ESOM algorithm, which is quite elegant, but the version implemented in the Kohonen package is based on Euclidean distance.  How well each map unit represents the samples positioned within it is represented by the distance between the map unit and each sample.  This can be visualized with:

plot(som.model.edges, type = 'quality', pch = 19, palette.name = topo.colors)

Units with shorter distances in the plot above are better defined by the samples in those units than units with long distances.  What distance is good enough depends on your data and objectives.

The next piece is trickier because there’s a bit of an art to it.  At this point each sample has been assigned to one of the 25 units in the map.  In theory we could call each map unit a “segment” and stop here.  It’s beneficial however, to do an additional round of clustering on the map units themselves.  Particularly on large maps (which clearly this is not) this will highlight major structural features in the data.  Both k-means and hierarchical clustering work fairly well, anecdotally k-means seems to work better with smaller maps and hierarchical with larger maps, but you should evaluate for your data.  Here we’ll use k-means.  K-means requires that you specify the number of clusters in advance, which is always a fun chicken and egg problem.  To solve it we use the within-clusters sum of squares method:

wss.edges <- (nrow(som.model.edges$codes)-1)*sum(apply(som.model.edges$codes,2,var)) for (i in 2:15) {   wss.edges[i] <- sum(kmeans(som.model.edges$codes, centers=i)$withinss) } plot(wss.edges,      pch = 19,      ylab = 'Within-clusters sum of squares',      xlab = 'K')

Here’s where the art comes in.  Squint at the plot and try to decide the inflection point.  I’d call it 8, but you should experiment with whatever number you pick to see if it makes sense downstream.

We can make another plot of the map showing which map units belong to which clusters:

k <- 8 som.cluster.edges <- kmeans(som.model.edges$codes, centers = k) plot(som.model.edges,      main = '',      type = "property",      property = som.cluster.edges$cluster,      palette.name = topo.colors) add.cluster.boundaries(som.model.edges, som.cluster.edges$cluster)

Remember that the real shape of this map is a toroid and not a square.  The colors represent the final “community segmentation”; the samples belong to map units, and the units belong to clusters.  In our paper we termed these clusters “modes” to highlight the fact that there are real ecological properties associated with them, and that (unlike clusters) they support classification.  To get the mode of each sample we need to index the sample-unit assignments against the unit-cluster assignments.  It’s a little weird until you get your head wrapped around it:

som.cluster.edges$cluster[som.model.edges$unit.classif] [1] 5 7 7 5 2 7 5 3 7 5 2 6 1 1 1 7 5 4 7 7 5 7 7 7 7 7 7 1 4 4 4 4 7 7 7 6 6 6 6 1 1 1 7 5 5 5 1 1 1 5 5 7 7 4 8 7 7 4 7 8 [61] 7 7 7 7 6 5 6 7 7 7 6 4 6 5 4 4 6 2 1 1 1 1 1 4 1 4 4 4

A really important thing to appreciate about these modes is that they are not ordered or continuous.  Mode 4 doesn’t necessarily have more in common with mode 5 say, than with mode 1.  For this reason it is important to treat the modes as factors in any downstream analysis (e.g. in linear modeling).  For our analysis I had a dataframe with bacterial production, chlorophyll concentration, and bacterial abundance, and predicted genomic parameters from paprica.  By saving the mode data as a new variable in the dataframe, and converting the dataframe to a zoo timeseries, it was possible to visualize the occurrence of modes, model the data, and test the pattern of modes for evidence of succession.  Happy segmenting!

 

Always more

Side trip to Hiron Point, Sundarbans

Geohazards in Bangladesh - Tue, 01/31/2017 - 10:32
Our group returns on the country boat, the M.V. Sundari, from their morning fieldwork.

Our group returns on the country boat, the M.V. Sundari, from their morning fieldwork.

My critical equipment repairs were now done. Chris and Dan still had several days of work in the area, but Humayun and I were interested in traveling to Hiron Point near the coast in the Sundarban Mangrove Forest. We want to take advantage of being so close to We hoped we could do it in a day, with the tides and broad open channel to the south, it would take two, too much for Chris to spare. We worked out that Humayun, Liz and I could take Bachchu’s smaller boat, the M.B. Mowali. Mowali are the honey collectors in the Sundarban and Bawali are the wood cutters.

Chris measuring the reflectance spectra of the ground while some local woman look on.

Chris measuring the reflectance spectra of the ground while some local woman look on.

Before we leave, we have one day with Chris and the others. After, Matt and Tanjil, our forest guide from 2015 who stayed with us for a day, departed, I went out with them to Polders 32 and 31 for their afternoon run. They are making soil salinity measurements to see if it is possible to determine soil salinity from satellite imagery. Saline soils are a large problem in this part of Bangladesh. We took the country boat to shore and scouted for the appropriate place. At each one Chris and Dan laid out a grid of probes to measure salinity and moisture

Dan measuring the salinity of the soil.

Dan measuring the salinity of the soil.

content. Kingston and Zahan did similar measurements at the surface and at the root level. As always, we attracted a crowd of onlookers curious as to what these foreigners were doing.

Later, after dinner, the M.B. Mowali arrived and our group split once again. We traveled to the edge of the Sundarbans that night, to pick up our guide and our armed guard for the tigers. The Mowali is much smaller. I

Chris providing a detailed explanation of what he is doing in English to people who only speak Bangla.

Chris providing a detailed explanation of what he is doing in English to people who only speak Bangla.

haven’t seen her since she was renovated. Now there is one cabin, which Liz got, and a larger room for Humayun, myself and our guide. In the early morning we headed south. Once the fog lifted and we entered smaller channels, we started seeing deer and monkeys on the banks and in the forest. We stopped in a small side channel and had lunch before crossing the over 10-km wide estuary in our speed boat, a 40-min ride. I could see that a lot on fresh land had grown at the mouth of the channel with the forest station and our GPS since the

Liz gets photographed with two young girls. Blonde women doing field work is not that common here.

Liz gets photographed with two young girls. Blonde women doing field work are not that common here.

last time I was here, two years ago.

We brought along lots of extra equipment in case anything had broken down. Humayun and I worked on downloading the GPS data while Liz and the guide went for a walk and climbed the observation tower. They got to see deer, wild boar and a monitor lizard, while Humayun and I sat in a dark room. As usual, we struggled to remember how to connect and download data exacerbated my unfamiliarity with the Windows OS on the PC we were using.

The M.B. Mowali, our home for the next two days for the run to Hiron Point and back.

The M.B. Mowali, our home for the next two days for the run to Hiron Point and back.

Eventually, we got it right and were happy to see that the system was working perfectly, data files for every day since I last visited. Obviously, because we had brought all the equipment along, we didn’t need it. We downloaded all the data and then changed the SIM card in the modem. We had set up cellular communications when we installed the station, but the signal was too weak to every collect any data. Now there is a good signal here from a different cell phone company. When we get back we will have UNAVCO check to see if it works. In any case, we now have enough data to measure the subsidence here.  The sinking of the land exacerbates the impact of rising sea level. Only the vast sediment supply of the delta counters it to maintain the land. And that is at risk from human intervention.

Humayun having tea in the morning on the Mowali.

Humayun having tea in the morning on the Mowali.

We had tea and cookies with the forest ranger and then headed back before low tide trapped us in the channel. As things went well, we stopped on the newly emerged char land and Liz and I walked around examining the sediments, surprisingly sandy for a tidal estuary. Back in the speed boat, we crossed the broad channel and then paused to watch the sunset on the water. Once on the Mowali, we sailed to where we would spend the night in the Mangrove Forest and now I got to see deer and boar on

Sundarban Mangrove Forest at low tide.

Sundarban Mangrove Forest at low tide.

the way before darkness descended. There was even a herd of 9 or 10 just across from where we rejoined the Mowali.

In the morning, we started heading north. Because it was very foggy, we stayed in smaller channels for a few hours before entering the main channel of the Pussur River. I spent the early morning before breakfast watching the forest go by and spotted a few more

One of the many chital, or spotted deer, we saw along the way.

One of the many chital, or spotted deer, we saw along the way.

deer. By noon we were out of the Sundarbans and ready to drop off our guard. I actually hadn’t seen him for the entire trip. We continued past the Rampal power plant. This a coal-fired plant being built less than 20 km from the Sundarbans. Most of the coal for it will likely be transported up the Pussur River through the Sundarbans. It is the subject of a lot of protests, including the hartal we had last week, but they are not likely to stop it from being built. A short time later we met up with the Bawali and

Getting into the speedboat to sail across the channel to Hiron Point.

moved back across. Then, work here being done, both ships sailed up to Khulna for the night. Tomorrow morning we disembark for the next phase of the trip.

Having tea with the forest ranger after completing our work.

Al fresco dinner on the Mowali.

Sunset over the Sundarbans and one of the many ships plying the waterway.

Equipment repairs in SW Bangladesh

Geohazards in Bangladesh - Tue, 01/31/2017 - 04:53
Having a breakfast of an omelet and paratha while waiting at the ferry ghat (dock) at Mawa.

Having a breakfast of an omelet and paratha while waiting at the ferry ghat (dock) at Mawa.

After a night in Dhaka, our group temporarily split up. Chris and Dan headed to Khulna in the SW at 4 am to avoid the hartal (general strike) that was planned for 6am-2pm. Liz and I stayed in Dhaka for a day. I spent it mostly editing material for a new project. The next day Liz, Humayun, my partner from Dhaka University, and I followed the others to Khulna, crossing the Padma (combined Ganges and Brahmaputra) River by ferry at Mawa. After waiting an hour, Humayun used a connection from a former student to get us on the next

Mofizur removing the antenna and antenna mount from the listing GPS pillar while I watch from the side.

Mofizur removing the antenna and antenna mount from the listing GPS pillar while I watch from the side.

ferry, a fast one. It is impressive how much the river has silted up since the last time I crossed here. Another few hours and we arrived at our compaction meter site SE of Khulna. We picked up one of the 4 sons from the family that takes care of the site. Mofizur, the second son, now a student at Chittagong University, is returning home for the first time in 6 months. Making the weekly measurements has been passed along from the oldest to youngest sons. It made for a great welcoming by the Islam family when we arrived mid-afternoon.

Me sighting through the optical level to get the relative elevations of the 6 optical fiber compaction wells.

Me sighting through the optical level to get the relative elevations of the 6 optical fiber compaction wells.

The last time I was here, the river adjacent to the site was being dredge and widened. It had gone from 200 m wide to just a few and was now too small for boats except at high tide. The widening cut into the bank that held our instruments. While the engineer tried to leave us enough room, it clearly didn’t work. The pillar that holds the GPS antenna is tilting badly towards the stream. They have secured it with ropes to keep it from completely falling over. We got hold of a ladder and removed the unusable antenna. Mofizur climbed up, afraid that I weighed too much for the fragile system. Next, Humayun and I surveyed the monuments for the compaction meter wells. We had to dig out the sediments

Liz measures and describing the sediments that have accumulated over the base of the wells since they were installed in 2011.

Liz measuring and describing the sediments that have accumulated over the base of the wells since they were installed in 2011.

covering the base. Liz measured the thicknesses, which were 4-7 inches. We could clearly see the finely layered sediments deposited from before the river was enlarged to the thick muds that accumulated afterwards. The sedimentation rate had clearly increased due to the river widening. The survey will give us the relative heights of the wells. When we get back we will compare it to earlier measurement to see if the wells have shifted, too. Without the GPS we cannot determine the absolute elevations. Our last task was to measure the lengths of the optical fibers in the wells. We brought along a new laptop to work with the electronic distance meter (EDM), but we found the recharger was still in Dhaka. We had forgotten it. With a dead battery and no way to recharge it, the measurements will have to wait until Humayun can send the recharger.

LunchKHLC

Mr. Islam serves some fish to Humayun, Liz (taking photo) and myself in their courtyard as part of the feast that they prepared for us.

While we were there, we were served lunch, a huge banquet. Three finds of fish, chicken, rice, vegetables, two desserts. The three of us sat a table outside in the yard, while the family plied us with the delicious home-cooked Bangladeshi food. The more important the guests, the more food and were were suitably overwhelmed. And since it was after 3 pm, we were famished and did our best make a dent in it. Since the GPS is no longer usable, we left them the battery and solar panel that was powering it, doubling their electricity supply. Before we installed the

The M.B. Bawali, our home for the next five nights and four days. Everything is great except for the cold water showers.

The M.B. Bawali, our home for the next five nights and four days. Everything is great except for the cold water showers.

equipment in 2011, they did not have electricity at all. After some heartfelt farewells, we headed to Khulna to meet up with Chris, Dan and Matt Winters, my TA from the class I taught in 2015. Fluent in Bangla, he has been working with Chris on field observations for his Master’s thesis at Columbia. He and some of his assistants will join us for a few days. The three of them had a dinner meeting, so my group headed to the M.B. Bawali, our home for the next 4 days. Smaller than the M.B. Kokilmoni, it is a perfect size for our group.

Humayun inspecting our equipment on the roof of a school on Polder 32. The tower is a meteorological station and our GPS antenna is on the back wall.

Humayun inspecting our equipment on the roof of a school on Polder 32. The tower is a meteorological station and our GPS antenna is on the back wall.

The next morning, we headed for Polder 32, the embanked island we have been studying. Humayun and I will visit the GPS station we set up there in 2012. It has a cellular modem so data can be downloaded remotely every day, but stopped working in November. It seemed that the receiver was not recording satellites, so we brought along replacement antennas, cables and lightning protectors. Another GPS station had a similar problem and there the cable had to be replaced. When we arrived at the school, we found the receiver was tracking satellites. We didn’t

Humayun stripping the end off the coaxial cable that we used as a grounding wire.

Humayun stripping the end off the coaxial cable that we used as a grounding wire.

have to track down a break in the system. But why wasn’t it recording data. The best we could ascertain was the modem had hung up; rebooting it fixed the problem. It was working, but I don’t understand what happened enough to be sure it won’t happen again. Hopefully, now that it is working, the engineers at UNAVCO can log in an work on it. When we doublechecked everything, we found that the grounding wire was missing. This is unsafe. If there is a lightning strike, the lightning protector blows the connection

A stopped to pay our respects to the small shrine in the schoolyard to Saraswati, the Hindu goddess of knowledge and education.

A stopped to pay our respects to the small shrine in the schoolyard to Saraswati, the Hindu goddess of knowledge and education.

to the equipment inside and shunts the electricity down the grounding wire. We cannot put a school full of children at risk. The only wires we had were the coaxial antenna cables. We stripped the ends off a partial cable and wired it between the cut ends on the roof and near the ground. We made a visit to the Hindu goddess of education and headed back to the ship having done all the repairs we could, and satisfied that the school was safe.

Heading back to the Bawali on the country boat after a successful day on the Polder (embanked island).

Heading back to the Bawali on the country boat after a successful day on the Polder (embanked island).

Back to Bangladesh to date earthquakes and more

Geohazards in Bangladesh - Fri, 01/27/2017 - 01:06

 

 

 

 

 

 

GroupWPolice

Our group, Dan, Liz, Chris and myself, posing with our police escort at the Amtali Resort

TreesFog

Trees peaking out from the fog in the early morning on the Rashidpur anticline. The anticlines are covered by forests and tea gardens (plantations)

It has been over a year since I was in Bangladesh after coming here twice a year for the previous five years. This will be a packed trip doing many different things, collecting samples, fixing equipment, visiting rivers and hopefully meeting with the public and government officials about the earthquake hazard. My paper last year showed that there is the potential for an earthquake of at least Mw8.2 here, an area with ~140,000,000 people. However, with no knowledge of when the last megaquake was or how often that comes, we don’t know when it might occur, in years or centuries. The article received widespread coverage in the press and caused a panic in the region. Now I feel an obligation to help steer things towards better preparation and building construction.
Our first task is related to a past earthquake. The last time we were here, Céline and I collected samples from an abandoned river that shifted ~20 km to the west. We think the shift was caused by an earthquake, but we don’t know if it

View of the banks of the Kushiara River in NE Bangladesh where we are looking to sample

View of the banks of the Kushiara River in NE Bangladesh where we are looking to sample

was a moderate M7 or a large M8.5. Either one could be pretty destructive to people living on the soft delta sediments. We now have dates for the samples. The 3 ages we got for the last sediments deposited before the shift, or avulsion, were 3800, 3800 and 3600 years ago. The method we used was OSL, optically stimulated luminescence, dating. It measures electrons trapped in quartz crystals. The electrons are so weakly trapped, that sunlight can set them free. Thus we date how long it has been since the sediment has seen the sun. The one

Chris on the boat taking a photo with the highway bridge over the Kushiara River in the background

Chris on the boat taking a photo with the highway bridge over the Kushiara River in the background

hitch is the possibility that when the sediment was transported down the river, not all the electrons were freed. This is known as incomplete bleaching and would result in too old an age. Our solution is to collect samples from the modern river to see if there is any residual age that would shift our estimate for the earthquake.
Four of us arrived together, Chris Small and Dan Sousa, who use remote sensing to study the changes in the delta: rivers, coastline, vegetation, Liz Chamberlain, a graduate student specializing in OSL and

A group of girls excited by the strange visitors to their village asked me to take their picture.

A group of girls excited by the strange visitors to their village asked me to take their picture.

myself. On arrival, we were met by Saddam Hossain and headed NE towards the Kushiara and Meghna Rivers. We stayed the first night in a “resort” in the folded hills of Sylhet where tea is grown. As a result of the attack on the Holey Artisan Bakery last year, the country is taking precautions. When we entered the Sylhet Division, we were met with a police escort. They stayed with us all through the nigh and their relief through the next day until we left the Division on our way to Dhaka. This is a new experience for me. It did have the

A set of colorful houses line the bank of the broad Meghna River. We continue south to find sampling sites.

A set of colorful houses line the bank of the broad Meghna River. We continue south to find sampling sites.

advantage of being able to drive without stopping for tolls and the police used their siren to help with passing cars. Still we only got to our room around midnight, a long drive after two long flights.
Our first stop was the Kushiara River, a bit upstream of the river avulsion, but above the lake that forms every summer during the monsoon. My concern is that the lake decants the sands so the sediments upstream and downstream of the lake are different. Thus we will sample both. We drove to the small town

Chris, Dan and Liz on the country boat scanning for good sampling sites.

Chris, Dan and Liz on the country boat scanning for good sampling sites.

of Sherpur and the police facilitated renting a small boat. Sailing along the river, we spotted a good spot where the bank was eroding and we could easily collect samples. This was as simple as cleaning a spot and then hammering an iron tube into the deposits. The main precaution is that the sample must not be exposed to light or it will lose all its electrons. We then decided to collect a sample from the river bottom from the boat. This proved more challenging and it took several tries to get the boat into the

I am hammering our iron pipe into the eroding cut bank to collect a sample without exposing the center of it to light so it can be use for OSL dating.

I am hammering our iron pipe into the eroding cut bank to collect a sample without exposing the center of it to light so it can be use for OSL dating.

correct depth of water and collect a sample with the sampler at the end of a several meter long augur. We found we had to work fast as the boat would drift in the strong current. By noon, we had our two samples and headed to the Meghna River on the way back towards Dhaka.
The much larger and more industrialized Meghna River was a bit more challenging. We need an area undisturbed by people. We rented a country boat at the ghat (dock) near the Bhairab Bazaar Bridge over the river and sailed off. After almost an hour on the river, we found it. The nose of a large island and an eroding cut bank nearby. The point of the island was protected by sand bars, so Liz and I got out and sampled the bottom with the augur. Not movement to worry about when the boat is aground. Then we headed to the cut back exposure and took our 4th and final sample. The set of samples is different then I envisioned, but with Liz’s guidance, they will fit the bill well. By the time we got back to the ghat it was dusk. Time for a slow and traffic filled drive to Dhaka. We got in just in time to rush off to our favorite restaurant for a celebratory dinner at our favorite restaurant before it closed. This trip is off to a great start.

Thanks, Station Obama: Scientists immortalize the former president in a way never seen before - Salon

Featured News - Sat, 01/21/2017 - 12:00
Quotes Lamont scientist Hugh Ducklow on Antarctic research location.

New paper published in ISME Journal

Chasing Microbes in Antarctica - Fri, 01/20/2017 - 19:36

I’m happy to report that a paper I wrote during my postdoc at the Lamont-Doherty Earth Observatory was published online today in the ISME Journal.  The paper, Bacterial community segmentation facilitates the prediction of ecosystem function along the coast of the western Antarctic Peninsula, uses a novel technique to “segment” the microbial community present in many different samples into a few groups (“modes”) that have specific functional, ecological, and genomic attributes.  The inspiration for this came when I stumbled across this blog entry on an approach used in marketing analytics.  Imagine that a retailer has a large pool of customers that it would like to pester with ads tailored to purchasing habits.  It’s too cumbersome to develop an individualized ad based on each customer’s habits, and it isn’t clear what combination of purchasing-habit parameters accurately describe meaningful customer groups.  Machine learning techniques, in this case emergent self-organizing maps (ESOMs), can be used to sort the customers in a way that optimizes their similarity and limits the risk of overtraining the model (including parameters that don’t improve the model).

In a 2D representation of an ESOM, the customers most like one another will be organized in geographically coherent regions of the map.  Hierarchical or k-means clustering can be superimposed on the map to clarify the boundaries between these regions, which in this case might represent customers that will respond similarly to a targeted ad.  But what’s really cool about this whole approach is that, unlike with NMDS or PCA or other multivariate techniques based on ordination, new customers can be efficiently classified into the existing groups.  There’s no need to rebuild the model unless a new type of customer comes along, and it is easy to identify when this occurs.

Back to microbial ecology.  Imagine that you have a lot of samples (in our case a five year time series), and that you’ve described community structure for these samples with 16S rRNA gene amplicon sequencing.  For each sample you have a table of OTUs, or in our case closest completed genomes and closest estimated genomes (CCGs and CEGs) determined with paprica.  You know that variations in community structure have a big impact on an ecosystem function (e.g. respiration, or nitrogen fixation), but how to test the correlation?  There are statistical methods in ecology that get at this, but they are often difficult to interpret.  What if community structure could be represented as a simple value suitable for regression models?

Enter microbial community segmentation.  Following the customer segmentation approach described above, the samples can be segmented into modes based on community structure with an Emergent Self Organizing Map and k-means clustering.  Here’s what this looks like in practice:

From Bowman et al. 2016.  Segmentation of samples based on bacterial community structure.  C-I show the relative abundance of CEGs and CCGs in each map unit.  This value was determined iteratively while the map was trained, and reflects the values for samples located in each unit (B).

This segmentation reduces the data for each sample from many dimensions (the number of CCG and CEG present in each samples) to 1.  This remaining dimension is a categorical variable with real ecological meaning that can be used in linear models.  For example, each mode has certain genomic characteristics:

From Bowman et al. 2016.  Genomic characteristics of modes (a and b), and metabolic pathways associated with taxa that account for most of the variations in composition between modes (d).

In panel a above we see that samples belonging to modes 5 and 7 (dominated by the CEG Rhodobacteraceae and CCG Dokdonia MED134, see Fig. 2 above) have the greatest average number of 16S rRNA gene copies.  Because this is a characteristic of fast growing, copiotrophic bacteria, we might also associate these modes with high levels of bacterial production.

Because the modes are categorical variables we can insert them right into linear models to predict ecosystem functions, such as bacterial production.  Combined with bacterial abundance and a measure of high vs. low nucleic acid bacteria, mode accounted for 76 % of the variance in bacterial production for our samples.  That’s a strong correlation for environmental data.  What this means in practice is; if you know the mode, and you have some flow cytometry data, you can make a pretty good estimate of carbon assimilation by the bacterial community.

For more on what you can do with modes (such as testing for community succession) check out the article!  I’ll post a tutorial on how to segment microbial community structure data into modes using R in a separate post.  It’s easier than you think…

Earth's Temperature Rises, Again - WNYC

Featured News - Thu, 01/19/2017 - 12:00
Jason Smerdon, a climate scientist with the Lamont-Doherty Earth Observatory at Columbia University, said the record temperature rise — for the third year in a row — is confirmation the earth is warming, and humans are causing it.

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