October 2012 IceBridge Antarctica resumes … Mission goal…monitoring the polar regions…Mission target… determine changes in ice cover and thickness, refine models for future sea level rise…Mission instruments…airborne geophysics. Good luck team.
The crews have spent the last few weeks in Palmdale, where the DC8 is based, for instrument installation and test flights prior to our move down to Punta Arenas, our home base for IceBridge Antarctica.
Instrument Run Down: We are flying with the same instrument suite as last year allowing us to see above, below and through the ice. Laser altimetry, for surface ice measurements, measured by the NASA Airborne Topographic Mapper, visible band photography, to allow for draped imagery, from NASA’s DMS (Digital Mapping System), three radar systems from Cresis to measure the ice thickness, composition and bed imagery (MCoRDS, Snow and KU band) and gravity to refine what is under the ice with Lamont using Sander Geophysics’ AIRGrav gravimeter.
ATM and the gravimeter both require GPS base stations on the ground throughout the deployment. Combined with the GPS receivers on the plane these allow very precise positioning of the aircraft, and the sensors on board, which is critical to all the measurements we make. Setting up the GPS stations is one of the first jobs in Punta Arenas.
Our First Mission for 2012 is Thwaites Glacier – Going Straight to the Heart of the Changes. On our way out of Punta Arenas, out past the airport, I noticed this feature in the landscape:
It appears to be the paleo-shoreline from the last interglacial (~80,000 yr BP), when sea level was higher than present. The very flat terrain results in any sea level change causing a large shoreline retreat. Evidence like this of changing shorelines, is one method scientists use to determine past sea level under a different climate. As we study different areas around the world, we must account for the local changes in how the land has risen or fallen. Changes in sea level can be a combination of an adjusted world/ocean wide (eustatic) sea level and the more local response from the rebounding (isostatic ) of the land that was previously depressed under a glacier as local ice is unloaded during deglaciation. Here the history of the shoreline was governed by a combination of changes in eustatic sea level and the isostatic response to deglaciation of the local ice load (De Muro et al. 2012). Putting together information from around the world we eventually build up a picture of the global changes that have occurred in sea level. Changes in sea level are directly connected to our work monitoring polar ice.
When we fly over the ice, we are monitoring how the ice sheets are changing at present, and learning how to understand the complicated interactions between the atmosphere, the ocean and the ice. Studying this helps us to understand which ice bodies are most likely to contribute to sea level, how quickly they changed in the past, and how quickly they might change in the future. It’s good to get this reminder as we head out on our first flight – especially as it is to survey the area where the glacier switches from being frozen to the land below [the bed] to where it goes afloat, called the ‘grounding line’.
Our first flight of the season will be along the Thwaites Glacier. Thwaites and Pine Island Glacier are two ‘glaciers of interest’, both large outlet glaciers that serve as conduits out of the ice mass of the West Antarctic Ice Sheet (WAIS), moving ice off the land into the surrounding ocean, and long considered its Achilles heel. Thwaites glacier has a very wide region of fast ice flow over its grounding line, and a relatively small change in that width has the potential to greatly increase the flux of ice into the ocean. Through the radar and gravity measurements collected on previous IceBridge missions we have been able to get a sense of the bed shape tipping downward as you move inland from the ice edge, and where pockets of water lie under the icesheet. Our goal today is to collect enough data to develop a more complete image of what lies under the ice in this area.
2009 Operation IceBridge surveyed a grid in front of Thwaites grounding line and identified a ridge in the rock of the sea floor. In the last few months a large section of Thwaites glacial tongue broke off just seaward of that ridge. This mission will fly back and forth along nine lines parallel to the grounding line of Thwaites glacier. In combination with flights from previous years, this will give us a map of the grounding zone at 2.5 km spacing.
We are hoping to learn more about goes on underneath this icy reach of the Earth each time we take flight.