The R/V Marcus G. Langseth completed the initial portion of the NoMelt experiment on Dec 29, 2011. In the subsequent year, scientists began analyzing the active-source seismic data collected on that cruise, constructing initial models of the oceanic plate. The full analysis awaits the so-called “passive source” data – the year-long recordings of earthquakes and natural electrical and magnetic signals on the instruments that remain on the seafloor.
On Dec. 18, 2012, the R/V Melville departed San Diego to recover remainder of the NoMelt instruments and data. The expedition includes two scientists from Columbia’s Lamont-Doherty Earth Observatory: Post-doctoral scientist Patty Lin and graduate student Natalie Accardo. Natalie is sending regular reports from the ship, and I will post them here.
Post 1: Natalie Accardo, Dec. 19, 2012.
In the early hours of Dec. 18, a team of scientists aboard R/V Melville set out from San Diego to a remote portion of the Pacific Ocean on a trip that will take 28 days and cover more than 8,500 kilometers. On this voyage, we aim to recover 27 ocean bottom seismographs (OBS) instruments that have been sitting silently on the ocean floor for nearly a year. Throughout their stay on the seafloor, the OBS have been continuously listening and recording the shaking caused by distant earthquakes all over the world. By recording ground motion, we can constrain seismic wave properties and in turn the geologic characteristics of the oceanic plate. With this information, we hope to answer the multilayered question of what defines a tectonic plate.
For decades, geologists have focused most of their attention on locations where tectonic plates come together (i.e. subduction zones like Japan) and break apart (i.e. rift settings like the East African Rift System). Yet to better understand the complex processes happening at those sites, we must first understand the fundamental characteristics of a tectonic plate. For further information concerning instrument deployment and other aspects of this project, please refer to previous blog entries.
It takes seven days to make the 4,300 km journey from San Diego to the NoMelt OBS sites. During the transit time, we use instruments aboard the Melville to map topography and gravity of the ocean floor. Additionally, at regular intervals we toss “drifter” instruments overboard. These so-call “instruments of opportunity” were designed by students at the University of California San Diego (UCSD) to be deployed by any research vessel traveling through an area of interest. They are completely autonomous and will record sea surface information (temperature, salinity, etc.) wherever the currents take them, data that will be of use to oceanographers at UCSD.
Today marks only our second day on board and has given us our first true glimpse of the open ocean. Rocky seas have confined most of the science party to their bunks in a group effort to retain what is left of our last meal. However, the promise of calmer weather in the coming days has brought some cheer to the entire crew.
Currently email service is down for most users due to multiple hardware failures. We are working on the problem. There is no estimate as to when we will be back up.
Mail service for many users is down due to mutiple hardware failures. We are working on the problem.
1500 feet above the ground surface is where our suite of instruments normally operates, but for this flight we are taking them up higher, much higher, in fact over 20 times our normal range to 33,000 feet. Our flight plan is to repeat lines surveyed in a previous years by NASA’s Land, Vegetation Ice Sensor (LVIS) a scanning laser altimeter. LVIS has collected data as part of the IceBridge instrument suite in the past, but it was flown separately at high altitude on its own plane, in order to map large areas of both land and sea ice. This flight will refly some of LVIS’s work but using a subset of the instruments on our plane, narrow swath-scanning lidar, the digital mapping camera system, the gravimeter, and our depth radar.
At our higher elevation we will fly faster and can cover a lot of ground. The landscape of Antarctica can be hard to get ones head around – a glacier catchment is usually too big to fit into one field of view, so we see it bit by bit, and try to build up a physical picture in the same way we build up our understanding of the system – piece by piece. We have flown several missions into the Amundsen Sea region on the west Antarctic coast in the past, but this was the first time where we could really see the context of all of these different glaciers – flowing into the same embayment, forming ice shelves, calving ice bergs, and drifting northwards through the sea ice.
The flight offers views of some of the most noteworthy features in Antarctica. Pine Island Glacier, one of world’s fastest streaming glaciers, developed an 18 mile crack along its face in the fall of 2011 which spread further over the last few months. The crack will inevitably lead to breakage, dropping an iceberg which scientists have estimated will be close to 300 pound in size.
Bordering the glacier is one of two shield volcanoes we passed over during our flight. Pushing up through the Antarctic white mask, Mount Murphy diverts the ice streaming along the glacier. A steeply sloped massive 8 million year old peak, Mount Murphy pulls my thoughts back New York as it was named for an Antarctic bird expert from the American Museum of Natural History.
From Mount Murphy we continue to the second shield volcano, Mount Takahe. Ash from 7900 years ago found in an ice core from the neighboring Siple Dome has been attributed to an eruption from this volcano. This massive potentially active volcano is about 780 cubic kms in size. The volcano was named by a science team participating in the International Geophysical Year (1957-8) after the nickname of the plane providing their air support …an unusual name for a plane as its origin is that of a plump indigenous Māori bird from New Zealand which happens to be flightless! Regardless the rather round Mount Takahe soars high above the glacier as we move overtop.
From there we fly over the tongue of Thwaites Glacier as it calves icebergs into the Amundsen Sea. To read more about Thwaites check out my first blog of the season: http://blogs.ei.columbia.edu/2012/10/18/launching-the-season-with-a-key-mission-icebridge-antarctica-2012/
For more on the IceBridge project visit:
Named after Edith Ronne, the first American woman to set foot on this southern continent, the Ronne Ice Shelf is tucked just to the East of the Antarctic Peninsula on the backside of the Transantarctic Mountains. With an area measured at 422,000 square kms, this is the second largest ice shelf in Antarctica. This vast icy expanse stretches into an indentation in the Antarctic coastline called the Weddell Sea, and gained some attention this past spring when scientists identified a mechanism that will force warming ocean water up against Ronne, which over time will cause it to thin and weaken (Hellmer, H. H. et al., 2012). Ice shelves are important barriers slowing the flux of ice moving off the land into the surrounding ocean. Any weakening in the tight connection of this ice to the land, either at the bottom where the shelf freezes to the ground below or where at the edges where it is tightly fused to the continent, can have major impacts on the speed and volume (flux) of ice moving off the land and into the oceans.
The current mission is being flown to measure the flux of ice currently coming into the Ronne Ice Shelf from the surrounding Antarctic landmass. To determine this we focus on the ‘grounding line’, the area where the ice changes from being frozen solid to the land below to floating as part of the ice shelf. To understand how much ice is moving over the grounding line, we have to understand how much ice is at the grounding line, and to do this we have to fly along the grounding line (or slightly inshore of it).
In many areas of Antarctica, even knowing where the grounding line is takes a lot of work. Much of that work is done using satellite data through a process called “interferometry”. This process compares the returning radar signal from different satellite passes to determine where the ice begins to move under the influence of the ocean tides. In this scale, ice that is responding to the rise and fall of the tides is floating ice, and from this we can mark the grounding line. While technique identifies the grounding line, it does not show how much ice is moving across it; to determine that we need to collect ice thickness measurements. For today’s flight we moved just inland of the grounding line for about half of the Ronne Ice Shelf collecting ice thickness and other supporting data that will begin to fill in this important information.
Reference: Hellmer, H. H. et al. Nature, 2012. DOI:10.1038/nature11064.
For more on the IceBridge project visit:
By Ana Camila Gonzalez
“But can’t you see the rings already?” I ask, wondering why I’ve been asked to sand a sample- it sounds to me like one would damage a sample by subjecting it to the mechanical screech of a sander.
“Yes, but under the microscope they look foggy if you don’t sand them. Also, you’re looking at a black oak sample. You wouldn’t see any rings before sanding if you were looking at a Maple, for example.” Jackie responds. She shows me a maple core sample that she explains has been hand-sanded down to a 1200 grit. It’s smooth and shiny as can be; yet I can barely see what seem to be hairlines.
“Oh. That makes sense.” I secretly hope I won’t have look at another maple sample for a while.
I approach the machine. I look like a character from BioShock or a WWII soldier in the trenches, as I am wearing a respiration mask, goggles and ear muffs. Seemed a little excessive to me at first- once I turned the machine on and I saw the mushroom cloud of sawdust come off the banshee-screeching sander, however, I realized I’d be better off looking like a biohazard worker than having to bring an inhaler and hearing aid to work.
I place my first sample down on the sander, but it flies off and hits the wall… I guess I can hold it tighter and push it down a little harder. I try again but this time my sample stops the belt from spinning. Definitely too hard. Eventually I get just the right amount of pressure, and I realize I can tell because my sample looks clearer every time I take it off the belt. I start humming to myself, singing something along the lines of I can see clearly now, the rings are there… As I go to higher and higher grits and my sample starts developing a cloudless luster, I realize I enjoy this a little too much.
To me, sanding is a process full of Zen. It’s a process I can focus on while still letting my mind wander, and my thoughts usually get pretty philosophical- I have this foggy, unclear sample and slowly I take off its layers and layers of disparities. What results is a core in its purest form ready to tell the story of its life, and after a few hours of sanding I’m ready to listen.
Ana Camila Gonzalez is a first-year environmental science and creative writing student at Columbia University at the Tree Ring Laboratory of Lamont-Doherty Earth Observatory. She will be blogging on the process of tree-ring analysis, from field work to scientific presentations.
One piece of our IceBridge mission focuses on sea ice here in the south. Sea ice in the northern regions has been reducing at dramatic rates over the last decade, setting a new record just this year, but the story in the south is not so clear. In fact, there has been a buzz that Antarctic sea ice extent may just be increasing while the Arctic ice is decreasing. The issue is a complex one and involves not just sea ice extent (how much surface area the ice covers) but sea ice thickness (total volume of ice). While the extent of Antarctic sea ice is increasing, we also need to understand how the thickness is varying.
One of the trickier items in measuring sea ice is making the raw measurements of thicker and thinner ice. With only satellite measurements it is hard to get the true thickness of the ice, since the surface of the ice is often covered with snow that needs to be accounted for in our calculations. Using the snow radar on the IceBridge mission we can work out how much of what the satellite is measuring is actually snow.
The Bellinghausen Sea sits just to the west of the Antarctic peninsula and in the southern winter months is generally covered with sea ice. We have flown two Bellinghausen sea missions this season – one to map out to the furthest edges and another to looks at the gradient of sea ice change as you move away from the coast or shoreline. The second Bellinghausen mission was important because in running profiles in and out from the coast it allowed us to measure how ice thickness patterns vary with distance from the shore. We need to understand these patterns of ice thickness in the southern end of the planet, how they may be changing and what connection they have to the climate system.
There has been much less study done on southern sea ice than northern sea ice because we get very few opportunities to make the measurements we need. We have two high priority flights to the Weddell Sea (on the eastern side of the Antarctic peninsula), but so far it has not been possible to fly them because of the weather. Hopefully before the end of this season we will be able to fly both these flights and fill in more pieces in the sea ice story.
For more on the IceBridge project visit: