Operation Icebridge : Scientists Map Thinning Ice Sheets in Antarctica
Climate change has weakened the ice sheets of western Antarctica. Scientists from Lamont-Doherty are flying over the region on a NASA-led mission called Ice Bridge to understand what's happening on and below the ice. What they find may help predict future sea level rise.
Team: James Cochran
Purpose: Airborne Polar Research
Date: Sep. 2009 -2014
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:
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:
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:
Last year IceBridge had its first flights into East Antarctica when it flew some missions into the Recovery Glacier area. Recovery is a section of Antarctic ice that lies east of the peninsular arm of West Antarctica, tucked behind the Transantarctic Mountains, a dividing line that separates west from east. We know from Satellite data that Recovery and its tributaries have a deep reach, stretching well inland to capture ice and move it out into the Filchner Ice Shelf draining a large section of the East Antarctic ice sheet. But there is a lot we don’t know about Recovery because the remoteness of the area has limited the number of surveys.
Several recent works have showed us that this area is important. Satellite measurements of the ice surface show small patches along the trunk of the glacier that are changing elevation more than their surroundings. These patches have been interpreted as lakes that lie under the ice sheet, coined the Recovery Subglacial Lakes. The lakes appear to drain and refill over time as the surface elevation over the lakes changes. To learn more about them and what they might tell us about the behavior of the glacier, we need to look under the ice.
But there is more we need to understand about this remote area, including simply needing to know the size and shape of the channel that delivers this ice out to the ice shelf and towards the Weddell Sea. Last year’s mission gave us some data points to outline the channel, but this year will help us provide a more complete imaging of what lies below this East Antarctic ice conveyor belt.
We will fly cross sections along the lines of the retired ICESat satellite tracks, allowing us to compare the laser measurements we make of ice surface elevation to those made during the satellite mission. We will end the day flying along the Recovery channel to get another look at one of the interpreted lakes. Combining last years’ data, ICESat data and this year’s data will give us a better picture of the area that has been carved beneath the Recovery glacier, the amount of ice that can be moved through the glacier and its tributaries, and how the lakes under the ice might fit into the larger story.