Antarctic ice appears in a range of types and sizes, from the newly formed skim of ice on the ocean called grease ice (above), to the older meter thick layers of sea ice, to chunks of icebergs, floating reaches of ice shelves, and finally the massive land based Antarctic ice sheet. Each part of this ice inventory has a unique role in the larger climate system, but they also work together. As part of this year’s IceBridge Antarctic flight campaign, we are focused largely on the coastline to build a better understanding of the interaction of these different pieces in the ice system. This understanding is central to improving our climate models.
The focus today is on Getz ice shelf. Ice shelves form when ice flows off the land into the surrounding ocean, forming a thick apron of attached, but floating ice. The Getz shelf extends out several miles from where the glacier empties into the ocean. The shelves are deep floating blocks of ice ~ a km thick where they first meet the ocean and thinned to several hundred meters thick at their front edge. They are critical for the future stability of the Antarctic ice sheet as they provide a barrier that holds back the continental ice sheet, braking its flow from land into the ocean.
In all ~ 45 ice shelves adorn almost half the Antarctica coastline, and represent an area of ~1.5 million km², close to 10 percent of the total ice that covers Antarctica. Ten of these are considered major shelves, with the largest two nestled in the junctures where East and West Antarctic meet, filling in the space with California-sized blocks of ice: the Ross Ice Shelf (at 472,960 km²), where Lamont-Doherty currently has another Antarctic research project called Rosetta running, and the Filchner-Ronne (422,420 km²) across from it. Many of the shelves are smaller, yet each serves a valuable role in Antarctic ice stability, and thus they are a prime focus for examining change in Antarctica.
Changes in Antarctic ice have been dominated by the interaction of the ice and the ocean, and because ice shelves extend out into the water, they are vulnerable to melt from the warmer ocean water. Melt can affect them in two ways, through thinning along their length and through causing a retreat of the “grounding line.” The grounding line is the critical spot where the ice goes from being frozen all the way to the ocean floor (or bed) to where it begins to float in the ocean. The grounding line retreat results from warm water melting the ice back from its frozen base. Tracking any changes to the location of the grounding line tells us a lot about the vulnerability of the ice shelf and is critical to setting models.
Getz ice shelf is our furthest flight mission of the campaign at close to 12 hours of flying, and it is our fifth mission this week, with each one clocking 11 plus hours of flight with prep and wrap-up added on either end. It could feel a bit like a rerun of the same movie, but it never does, and the wear of the long days doesn’t appear to show on the team. The purpose of today is to continue mapping the sub ice-shelf bathymetry using our gravimeter, as well as the ice surface and bedrock upstream of the grounding line using laser and radar. We need a complete look at the grounding line and the bed under the ice shelf, where warm ocean water can move in and circulate under the ice, in order to improve our models. Gravity is critical for uncovering the surface depths and contours under the ice shelves, as none of the other instruments on board are able to collect data through the water that lies under the shelf.
Because of the distance to Getz from our daily starting point in Chile, we have been building a set of data over a series of years, line by line. Each year we collect a repeat track and a new track. We know Getz has changed. Eighteen months ago in March 2015, a NASA image from space captured a Manhattan-sized iceberg (17 miles long) breaking off of Getz Ice Shelf. This break appears to have occurred at the end of the last austral summer in late February. Today we can see large sections of ice that will soon be calving, but what this means will need to be matched to the other measurements we are collecting before we know the full set of changes in Getz.
IceBridge: Since 2009, the NASA IceBridge project has brought together science teams to monitor and measure each of the ice features in order to improve our understanding of changes in the climate system and our models. Lamont-Doherty, under lead scientists Jim Cochran and Kirsty Tinto, has led up the gravity and magnetics measurements for these campaigns. This season alone, the project has logged 195 hours of flight time to date, and flown an equivalent of a third of the way to the moon.
A new film takes viewers from the eastern highlands of India to the booming lowland metropolis of Dhaka, the capital of Bangladesh–and explores an ever-more detailed picture of catastrophic earthquake threat that scientists are discovering under the region.
Scientists from Columbia University’s Lamont-Doherty Earth Observatory, the University of Dhaka and other institutions have been working for more than a decade to understand deeply buried geologic structures that could produce earthquakes here, one of the most densely populated places on earth. No one can predict when the next quake will strike, or how big it will be–but clearly there is potential for a very large one. “Some of this have long suspected this hazard, but we didn’t have the data and a model,” says Lamont-Doherty geophysicist Michael Steckler, leader of a recently published study outlining the threat.
Under Bangladesh, India and neighboring Myanmar, the scientists have found signs of a megathrust–the meeting of two gigantic moving tectonic plates, with one diving under the other. But the plates don’t seem to be moving right now; they are locked, and strain is building. The researchers say that when–not if–the plates do slip, destruction and casualties could be massive. Some 140 million people might be affected.
The hazard has been hard to assess up to now, because most of the region’s underlying geology is covered by the world’s largest river delta–miles-deep layers of sediment carried down from the Himalayas and built up over millennia. The team has deployed seismometers, GPS instruments, satellite imagery and other technology to draw up a picture of what is going on down below.
The region is unprepared. Not only are many people too poor to build earthquake-resistant structures. “From history, there’s been a lot of destructive earthquakes in this area, but there hasn’t been one in recent years, so people tend to forget,” said Lamont-Doherty geologist Leonardo Seeber. Geologist Humayun Akhter of the University of Dhaka, said, “Our cities are not built in a planned way, and this cannot be changed in a few years. So we have to work within this system, and teach our people how to cope.”
The movie was made by filmmakers Douglas Prose and Diane LaMacchia with support from the U.S. National Science Foundation. The NSF also funded the research.
The American Geophysical Union (AGU) election results are in, and three Lamont-Doherty Earth Observatory scientists will be taking key leadership roles in the internationally influential Earth and space sciences organization: polar explorer Robin Bell will become AGU president-elect, Kerstin Lehnert will join the Board of Directors, and Robert F. Anderson will become Ocean Sciences Section president-elect.
This is an exciting time for the Earth sciences as innovations in technology, expanding computational capacity, and global challenges open new avenues for research. It’s also an exciting time for the AGU. Bell will serve as president-elect for two years, then become president in 2019, the year the AGU celebrates its 100th anniversary.
The professional scientific organization has more than 60,000 members in 139 countries. Its Fall Meeting is the premier opportunity for scientists from across disciplines to share their latest research and develop new collaborations.
President-Elect Robin Bell
Bell credits AGU for helping build research connections in her own field, and she sees a greater role for AGU in communicating science and connecting scientists across the disciplines for innovative work.
“AGU is becoming increasingly relevant to major societal challenges, including hazards and climate change,” she said. “With growing breadth and relevance come opportunities and risks. AGU must continue to enable discovery, connection, and sharing ideas for our large, international, and diverse community through both our meetings and our publications.”
Bell, a Palisades Geophysical Institute/Lamont Research Professor, is one of the world’s leading experts in polar science. She directs research programs in Antarctica and Greenland; leads research on ice sheets, plate tectonics, and rivers; and leads the development of technology to monitor our changing planet. As chair of the National Academy of Sciences Polar Research Board, she was instrumental in launching International Polar Year 2007-2008, a major multinational push to study the polar regions.
As AGU president-elect, Bell will chair the AGU Council and serve as vice chair of the AGU Board for the next two years before moving into the president’s role as scientific leader for the AGU and its public spokesperson. Lamont’s founding director, Maurice “Doc” Ewing, and its current director, Sean Solomon, have both served as AGU president.
Director Kerstin Lehnert
Lehnert, a geochemist and Doherty Senior Research Scientist at Lamont, is director of the Lamont-based Interdisciplinary Earth Data Alliance (IEDA), which archives data from a wide range of geochemistry and marine geology sources and makes such data openly available with visualization and analysis tools for multidisciplinary work.
As a member of the AGU Board of Directors, Lehnert said she would like to see a greater AGU focus on developing programs and initiatives to promote interdisciplinary research and recognize the achievements of interdisciplinary researchers.
“There is an urgent need for AGU to implement change in its governance structure and programs to create new opportunities and incentives for cross-disciplinary science, fostering interdisciplinary exchange, and collaboration among researchers both within AGU and through partnerships with other societies,” she said.
Ocean Sciences President-Elect Robert Anderson
Anderson said he plans to urge AGU to focus on its core mission in service of its membership. “Science is being squeezed by funding, politics and other forces so AGU members need to have a strong organization advocating on their behalf,” he said.
Bell, Lehnert, Anderson, and the other AGU leaders elected this week will start their new roles in January.
“AGU is the largest professional society in the Earth and space sciences in the world, and its members span every discipline across those fields,” Lamont Director Sean Solomon said. “It is fitting that Lamont, given our extraordinary breadth of expertise, should now be the home to three of AGU’s next leaders, including the scientist who will oversee the Union’s transition to its second century.”
Lamont-Doherty Earth Observatory is Columbia University’s world-renowned home for Earth and environmental research.
I’m very excited that our manuscript “Microbial community dynamics in two polar extremes: The lakes of the McMurdo Dry Valleys and the West Antarctic Peninsula Marine Ecosystem” has been published as an overview article in the journal BioScience. The article belongs to a special issue comparing different ecological aspects of the two NSF-funded Long Term Ecological Research (LTER) sites in Antarctica. I’m actually writing this post on my return trip from the first ever meeting of the International Long Term Ecological Research (ILTER) network at Kruger National Park in South Africa (an excellent place to ponder ecological questions).
This article had an odd genesis; the special issue was conceived by John Priscu, a PI with the McMurdo LTER project. I was ensnared in the project along with Trista Vick-Majors, a graduate student with John Priscu (now a postdoctoral scholar at McGill University), shortly after starting my postdoc with Hugh Ducklow, PI on the Palmer LTER project. The guidance we received was more or less “compare the McMurdo and Palmer LTERs”. How exactly we should compare perennially ice-covered lakes in a polar desert to one of the richest marine ecosystems on the planet was left up to us. Fortunately, microbial ecology lends itself to highly reductionist thinking. This isn’t always helpful, but we reasoned that on a basal level the two ecosystems must function more or less the same. Despite dramatically different physical settings, both environments host communities of phytoplankton (sometimes even similar taxonomic groups). These convert solar energy into chemical energy and CO2 into organic carbon, thereby supporting communities of heterotrophic bacteria and grazers.
To look at the details of this we stretched the bounds of what constitutes an “overview article” and aggregated nearly two decades of primary production and bacterial production data collected by the McMurdo LTER, and over a decade of the same from the Palmer LTER. By looking at the ratio of bacterial production to primary production we assessed how much carbon the heterotrophic bacterial community takes up relative to how much the phytoplankton community produces.
Typical marine values for this ratio are 1:10. At a value of around 1:5 the carbon demands of heterotrophic bacteria are probably not met by phytoplankton production (the majority of carbon taken up by bacteria is lost through respiration and is not accounted for in the bacterial production assay). Most of the lakes hover around 1:5, with values above this fairly common. Lake Fryxell however, an odd lake at the foot of Canada Glacier, has values that often exceed 1:1! Consistent with previous work on the lakes such high rates of bacterial production (relative to primary production) can only be met by a large external carbon subsidy.
Where does this external carbon come from? Each summer the McMurdo Dry Valleys warm up enough that the various glaciers at the valley peripheries begin to melt. This meltwater fuels chemoautotrophic bacterial communities where the glacier meets rock (the subglacial environment), and microbial mats in various streams and melt ponds. Like microbial communities everywhere these bleed a certain amount of dissolved carbon (and particulate; DOC and POC) into the surrounding water. Some of this carbon ends up in the lakes where it enhances bacterial production.
But external carbon subsidies aren’t the only part of the story. Nutrients, namely phosphate and nitrate, are washed into the lakes as well. During big melt years (such as the summer of 2001-2002 when a major positive SAM coupled to an El Nino caused unusually high temperatures) the lakes receives big pulses of relatively labile carbon but also inorganic nutrients and silt. This odd combination has the effect of suppressing primary production in the near term through lowered light levels (all that silt), enhancing it in the long term (all those nutrients), and giving heterotrophic bacteria some high quality external carbon to feed on during the period that primary production is suppressed. Or at least that’s how we read it.
Not a lake person? How do things work over in the Palmer LTER? One of the biggest ecological differences between Palmer and McMurdo is that the former has grazers (e.g. copepods, salps, and krill) and the latter does not, or at least not so many to speak off. Thus an argument can be made that carbon dynamics at Palmer are driven (at least partially) by top-down controls (i.e. grazers), while at McMurdo they are dependent almost exclusively on bottom-up (i.e. chemical and physical) controls.
At times the difference between bacterial production and primary production is pretty extreme at Palmer. In the summer of 2006 for example, bacterial production was only 3 % of primary production (see Fig. 4 in the publication), and the rate of primary production that summer was pretty high. The krill population was also pretty high that year; at the top of their 4-year abundance cycle (see Saba et al. 2014, Nature Communications). This is speculative, but I posit that bacterial production was low in part because a large amount of carbon was being transferred via krill to the higher trophic levels and away from bacteria. This is a complicated scenario because krill can be good for bacteria; sloppy feeding produces DOC and krill excrete large amounts of reduced nitrogen and DOC. Krill also build biomass and respire however, and their large fecal pellets sink quickly, these could be significant losses of carbon from the photic zone.
Antarctica is changing fast and in ways that are difficult to predict. Sea ice seems to be growing in the east Antarctic as it is lost from the west Antarctic, and anomalous years buck this trend in both regions. A major motivation for this special issue was to explore how the changing environment might drive ecological change. I have to say that after spending a good portion of the (boreal) summer and fall thinking about this, some of that time from the vantage point of Palmer Station, I have no idea. All of the McMurdo Lakes react differently to anomalous years, and Palmer as a region seems to react differently to each of abnormal year. I think the krill story is an important concept to keep in mind here; ecological responses are like superimposed waveforms. Picture a regularly occurring phenomenon like the El-Nino Southern Oscillation imposing a periodicity on sea ice cover, which we know has a strong influence on biology. Add a few more oscillating waves from other physical processes. Now start to add biological oscillations like the four-year krill abundance cycle. Can we deconvolute this mess to find a signal? Can we forecast it forward? Certainly not with 10 years of data at one site and 20 years at the other (and we’re so proud of these efforts!). Check back next century… if NSF funds these sites that long…
Many thanks to my co-authors for going the distance on this paper, particularly the lake people for many stimulating arguments. I think limnology and oceanography are, conceptually, much less similar than lakes and oceans.