Operation Icebridge : Scientists Map Thinning Ice Sheets in Antarctica

By Kirsty Tinto & Mike Wolovick – As little as a few decades ago you could ask a scientist what it was like to monitor the changing ice in Antarctica and the response might have been “Like watching paint dry” – seemingly no change, with no big surprises and not too exciting. Well times have changed! The Ice Bridge Mission is deep into its third Antarctic season collecting data on the condition of the continental scale ice sheet and the floating sea ice that surrounds it, and has noted some exciting results!

On a recent survey flight, which was designed to be fairly routine flying back and forth across the main trunk of Pine Island Glacier, a large crack was spotted in the floating ice tongue in the front of the glacier – a crack large enough to bury a building 16 stories high! This means more changes are coming in the future of this active ice stream!

Pine Island Glacier has been under intense focus as one of the fastest moving, and rapidly thinning glaciers in Antarctica. The planned survey was a grid back and forth across the main trunk of Pine Island Glacier. The pilots refer to this kind of survey as “mowing the lawn”. This type of data collection is essential for putting together a more complete ‘picture’ of the glacier surface, depth, and its underlying surface, and its ‘grounding line’. The ‘grounding line’, shown here as the white line running through the image of the survey plan, is the front edge of where the glacier is frozen all the way to the bottom surface beneath it. The glacier extends beyond the grounding line but as a ‘floating tongue’ of ice.

Glacial tongues can be many meters thick, but because they rest on water they are susceptible to warming from the water below. It is not unexpected for sections of the tongues of glaciers to break off – in fact for this glacier scientists expect to see it occur about twice a decade (the last notable occurrence was in 2007). It is, however, impressive to see it actually developing, and to realize the scale of the crack as it begins – at least 50 meters deep, and up to 250 meters wide! Yes this is much better than watching paint dry!

Lamont-Doherty Earth Observatory has been a partner in this NASA led project collecting airborne gravity. The Ice Bridge Mission is designed to fill the gap between two satellite missions, IceSat I and IceSat II, collecting data on ice thickness in both polar regions. IceSat II is intended to be in orbit in another 4 to 5 years.

The IceBridge mission has been having trouble getting flights up recently, which we have been assured is par for the course in this kind of work, but still it is frustrating! Here we are down in Punta Arenas waiting…waiting…waiting. We have faced a series of weather related stoppages and then the normal issues with equipment repairs causing this season to unfold with agonizing slowness. We were, of course, spoiled by all our successes of the prior campaigns, when flights seemed to lift off with uncanny regularity!

However, last week there was a period where the weather and airplane were in synch and we got three flying days in a row, one to the South Pole with my colleague onboard, and two that I was on along the Western edge of the Antarctic Peninsula. The targets of my two flights were the ice shelves, where the ice flows off the Antarctic continent and ends floating in the sea. (see image)

I was eager to be involved in these two flights along the Antarctic Peninsula as they were to survey the Getz and the Dotson ice shelves which involves flying over the Amundsen Sea and past Thwaites Glacier. These floating ice shelves appear in a line, Thwaites, then Dotson, and then Getz (moving from the direction of tip of the peninsula downward). I have been working on data that were collected last year from the Thwaites area so it was good to at least be flying in the ‘neighborhood’. The Dotson flight was particularly useful for me, since the grid flown over it can be connected in to the Thwaites grid, extending my survey area and our understanding of that area.

I hadn’t been on a science flight before, so everything was new to me. There is a network on the plane so we can all sit with our laptops and follow our position on the map, see where we are going, how high and fast we are flying, and other information. There are additional cameras looking forwards and downwards, so we have a wide field of view in addition to looking out the window (which we did plenty of!) (see image)!

The different kinds of ice we flew over captured my interest…from icebergs in the open water, to big plates of sea ice, the expanse of flat, floating ice shelves and the crevassed glaciers. Each has a function in the polar region and studying the movements, expanse, depth of each can tell us a different piece of information about our changing polar region. There was a lot of variation in what was all essentially ice. For this flight, however, the targets was ice shelves, where the ice is floating on the sea. Collecting gravity data, which is Lamont’s role in this project, is important on these surveys because while the other instruments can measure the top (laser), bottom and internal surfaces of the ice (radar), they don’t “see” all the way down to the sea floor. The gravity measurement is controlled by the bathymetry of the sea floor, as well as by changes in geology, so we can use it to model the sea floor. Knowing what is under the shelves, how the ice is “hinged” to the continent, and how the ocean water beneath is coming into contact with the ice flowing off the continent is important to understanding how that ice might melt or move in the future.

On the trip home, I sat in the jump seat in the cockpit, a real treat! We flew back in to Punta Arenas over vegetated valleys, the landscape still marvelous but very different from how we had spent the day (see image).

Operation IceBridge Antarctica ramps up for a second year of ice surveys.  Originating from Chile, a series of airborne missions will be flown almost daily from the airbase in Punta Arenas.  Using a DC-8 jet airliner, the flights will run up to 11 hours each as they cross Drake’s Passage and the Southern Ocean to reach their destinations of monitoring Antarctic sea ice, the Antarctic peninsula and the western edges of the continent, before returning back to Chile each night. Flights will include some low altitude (~1,500 ft.) flights, and a few high altitude flights (~35,000 ft.).  For this season we will re-fly some of last year’s lines as well as adding some new locations to the flight plans.  One area to be resurveyed is an area of ongoing change – the Pine Island Glacier. This year the project design includes flying further back over the major trunk of the glacial ice stream in order to better understand the broader glacier dynamics.  The sea ice flights are also of interest to the science community since Antarctic sea ice, unlike Arctic sea ice, is actually growing in extent. Developing a better understanding of why this might be occurring is extremely important to understanding the full Antarctic climate dynamics.

The instruments on the plane include laser to map and identify surface changes (Laser Vegetation Imaging Sensor [LVIS] & Airborne Topographic Mapper [ATM]), radar to penetrate through the snow/ice and image below providing information on the bedrock support and internal ice characteristics, and gravity to measure the size and shape of any ocean water filled cavities at the outlets of some of the main fast-moving glaciers. Before embarking on the actual mission, test flights must be flown to check each instrument.  The five-hour test flights cruise over and around the Mojave desert, with different flight lines planned to test different instruments.  To me the most exciting was a ‘pitch and roll’ over Lake Mead for the LVIS scanning instrument to collect surface topography data.  The pitch is like putting the plane on a seesaw and tipping it forward and backward – which feels very impressive, and shows up in the vertical acceleration felt by the gravimeter and the butterflies in my stomach!  The roll maneuver involves flipping the plane side to side (although not all the way over), and looks very impressive out the window!  The instruments performed well so we move on to Chile.

The DC-8 carries 40 passengers and the seats are pretty big, so after a comfortable long-haul flight we spend Wednesday setting up the ground station – a hut where LVIS, ATM and gravity all have GPS antennae set up outside – and getting the gravimeter ready to measure.  Our gravity team includes Jim Cochran, and me from Lamont and Kevin and Sean from the Sanders gravity group. Because the gravimeter must stay plugged in at all times, by NASA guidelines it must be monitored round the clock.  We switch on and off this duty and every six hours swap generators and refuel.  Easy.   However the wind is blowing 76 km/hr, and gusting to 94 km/hr, so walking out to the plane is a challenge.  The good thing about Punta Arenas is that there are not many things blowing around – anything not tied down blew away a long time ago!