Project 4342

The edges of the world's big ice sheets in Antarctica and Greenland hold the key to future sea level rise. Mass can be lost rapidly from these ice masses through icebergs breaking off, or through ice flowing into the ocean faster. Research over the last decade has shown that rapid changes in West Antarctica and Greenland can be driven by a number of physical processes that act to accelerate ice flow and iceberg formation. Much less is known about how the same processes affect ice dynamics in East Antarctica. This project will make detailed observations, at a pair of outlet glaciers draining a part of the East Antarctic Ice Sheet, of ice flow response to the formation of surface meltwater, changes in sea ice conditions and rifting/calving and melting at the ice-ocean contact. Understanding how these processes affect the flow of ice will help to improve computational models of ice sheets, and therefore projections of future sea level rise.

Research in Greenland has shown that the flow of ice sheets can respond to seasonal melting at the ice surface or at floating ice tongues: typically ice flows faster in summer than in winter, and changes in the length of the melt season may lead to sustained acceleration of the ice. Much less is known about seasonal ice flow changes in Antarctica. In this project, we have installed monitoring equipment at Sorsdal Glacier near Davis Station to observe directly changes in ice flow velocity and ice tongue melting, and acquired satellite imagery to extend these observations to larger parts of the Princess Elizabeth Land Coast.

Research in Greenland has shown that the flow of ice sheets can respond to seasonal melting at the ice surface or at floating ice tongues: typically ice flows faster in summer than in winter, and changes in the length of the melt season may lead to sustained acceleration of the ice. Much less is known about seasonal ice flow changes in Antarctica. In this project, we have installed a suite of equipment at Sorsdal Glacier near Davis Station. We are monitoring ice flow velocity, melting at the bottom of the floating part of the glacier and the collection and drainage of melt in surface ponds at the top, as the melt and drainage processes are expected to have an affect on ice flow. We are also acquiring satellite imagery to extend these observations to larger parts of the Princess Elizabeth Land Coast. In addition, we are making more detailed measurements of the geometry of the glacier to help modelling efforts. By chance, we were able to observe a previously unknown wintertime drainage event through satellite observations, and were able to follow this up with radar measurements of the near-surface part of the glacier, trying to determine where the water drained to.

While exploring the seemingly seasonal surface lakes on the Sorsdal Glacier in 2016-17, we discovered hidden water that stays liquid over winter. These subsurface lakes had also been seen by a Belgian team on a floating ice shelf the year before, but never on a grounded glacier. The accumulation of subsurface water may be an important precursor to calving of icebergs. To explore where the water flows and where it gets stored, we used three geophysics methods this year. We became the first team to use airborne radar to image these near-surface lakes. We also used seismic instruments to "listen" for sound made by water as it flows just below the ice surface, and used electrical measurements to find flowing water. We also made careful measurements of the energy budget of the ice surface to understand how much melting can happen to feed the lakes, and where.

The Greenland Ice Sheet was first observed to exhibit seasonal changes in ice flow velocities in the mid-1990s, and these were eventually linked in part to the meltwater production at the ice surface. Where that melt water is able to reach the base of the ice, it can cause an acceleration in sliding of the ice. Alternatively, where the seasonal melt water is able to flow along the base of the ice sheet and reach the ocean cavity under a floating ice shelf fringing the ice sheet, the injection of freshwater into the ocean can stir ocean currents that weaken the ice and also accelerate ice discharge into the ocean. Surface melt accumulation is also thought to help predispose ice shelves to break-up. While the effect of melting on ice sheet flow in the northern hemisphere was being studied in increasing detail, very little was known about the effect of surface melting on the Antarctic Ice Sheet. The fact that there are sizeable areas of the Antarctic Ice experience melting and accumulation of melt in surface melt ponds was not even widely appreciated in the glaciological community until 2016. The present project is one of the first globally to conduct a systematic on-the-ground study of a surface melt water system on the Antarctic Ice Sheet, with a Belgian study having targeted a floating ice shelf a couple of years prior to our operations commencing. We were able to determine that the seasonal formation of a surface drainage system at the Sorsdal Glacier near Davis Station had no detectable effect on the flow of the glacier, but also that melt water was being retained in the long-term by the near surface of the glacier, with active water flow in winter. That stored water is not visible from the air or in optical satellite imagery, which is why it has not received significant attention despite the fact that water storage may accelerate the breaking-off of icebergs from the ice sheet. By identifying and making detailed observations of the process of subsurface water storage, our study will help guide future research into the physics that controls the mass balance of the Antarctic Ice Sheet.