Icebridge : Scientists Map Thinning Ice Sheets in Antarctica

Blog Feature: Ice Bridge

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.

 

Expanding Our Vision Brings the Big Picture Into Focus

November 12, 2012

Mount Murphy rises through the ice sheet along the flank of West Antarctica, diverting the flow of ice around it (photo credit J. Yungel, NASA IceBridge Project)

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.

Crack along the front of the Pine Island Glacier as seen form the IceBridge forward facing camera.


The crack in the Pine Island Glacier as it is propagating further through the ice (Photo credit NASA IceBridge)


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.

Mount Murphy, one of two shield volcanoes we overflew on this mission. (Photo K. Tinto)


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.

Mt. Takahe a slumbering volcano that is believed to have deposited evidence of an eruption in the ice almost 8000 years ago (Photo K. Tinto)


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/

The calving front of Thwaites Glacier. The neighboring glaciers of Pine Island and Thwaites are moving ice off West Antarctica into the surrounding ocean at a rapid rate (Photo K. Tinto)


For more on the IceBridge project visit:

http://www.nasa.gov/mission_pages/icebridge/index.html

http://www.ldeo.columbia.edu/res/pi/icebridge/:

The Story at Ronne

November 08, 2012

Travel to the Ronne Ice Shelf involved passing by the Ellesworth Mountains. The range contains Antarctica’s highest peak, Vinson Massif at 4897 meters of elevation.

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.

Annotated Antarctic map showing the area of study.


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).

The majestic Ellsworth Mountains, formed about 190 million years ago, are the highest range in Antarctica, and steeper than the Tetons. Their original name, Sentinel Range, describes their posture, as they watch over the Weddell Sea and the Ronne Ice Shelf.


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:

http://www.nasa.gov/mission_pages/icebridge/index.html

http://www.ldeo.columbia.edu/res/pi/icebridge/

The ‘Skinny’ on Antarctic Sea Ice

November 01, 2012

Sea Ice on the left, touching up against an ice shelf along West Antarctica. (Photo from the camera in the belly of the plane). The plane is flying at ~1500 ft. of elevation – the estimated field of view is ~450 meters.

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.

Bellinghausen sea ice labeled to show open water (dark areas), dark grey ice (less than 15 cm thick) and thicker light grey ice. Image from the NASA IceBridge camera.


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.

An pice of land ice that has separated as an iceberg (shows with a bluish coloring, approximately 30-40 meters in length) travels trapped amidst the floating sea ice in Bellinghausen Sea, Antarctica.


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:

http://www.nasa.gov/mission_pages/icebridge/index.html

http://www.ldeo.columbia.edu/res/pi/icebridge/

A Recovery Mission

October 29, 2012

Shackleton Ridge bordering the Recovery Ice Stream East Antarctica. (Photo M. Studinger, NASA)

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.

Recovery Glacier with the lakes outlined in red. The yellow lines are the flight lines for the mission. (image courtesy of NASA IceBridge)

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.

Recovery Glacier with “Which Way Nunatak” projecting up through the snow. A nunatak refers to an exposed section of ridgeline, or a peak that projects though the ice or snow in an ice field or glacier. (Photo by J. Yungel, NASA IceBridge)

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.