Taking Ocean Depth Measurements for BELISSIMA Project
Between 2 and 8 December 2011 a small team led by Alain Hubert and Dr. Katherine Leonard completed the first survey of Southern Ocean properties near the Roi Baudoin ice shelf.
These measurements were made in support of glaciological work for the BELSPO-funded "BELISSIMA (Belgian Ice Sheet – Shelf Ice Measurements in Antarctica)" project, which seeks to understand the dynamics of ice sheet outlet glaciers and ice shelves along the Princess Ragnhild coast of Antarctica.
The team made ocean depth measurements using an echo-sounder then lowered an SBE19plus CTD (Conductivity – Temperature – Depth) instrument through leads and holes drilled in land-fast sea ice to measure the temperature, salinity, dissolved oxygen content, turbidity, and pressure at all depths in the ocean water in front of and in rifts penetrating the ice shelf.
Understanding the Antarctic Ice-Sheet Mass Balance
The Antarctic ice sheet primarily loses mass by iceberg calving and through melting at the interfaces between the ice sheet and the Southern Ocean. The latter process strongly influences the former, is the least-constrained term in the mass budget of the Antarctic ice sheet, and has the potential to be rapidly and significantly influenced by even very small changes in global climate.
In the Amundsen Sea and Antarctic Peninsula regions there have been recent and dramatic accelerations in the movement of ice towards the ocean due to changes in the water properties reaching the ocean-ice interface beneath ice shelves. Such processes have not yet been reported in East Antarctica, but there are many regions of the East Antarctic coastline where no oceanographic measurements have ever been made, including the region where we were working.
The Importance of Ocean-Ice Interactions
Circumpolar Deep Water (CDW) is a "warm" salty current of ocean water that circles the Antarctic continent at greater depths in the ocean than most parts of the Antarctic continental shelf, so it is very difficult for this water to reach the ice sheet. In some regions, deep troughs in the seafloor allow this water to spill onto the continental shelf and flow underneath ice shelves, but the water must exist at the same depths as the ice in order to melt the ice. Detailed bathymetric and hydrographic surveys of the Antarctic continental shelf are thus a critical component of research on the mass balance of the Antarctic ice sheet.
The BELISSIMA project is improving our knowledge of ice sheet-ice shelf / ocean interactions by investigating processes occurring where the ice sheet meets the ocean, including those in the sub-ice shelf ocean cavity. Measurements of the ocean properties at the interface between the ocean and the ice sheet are very difficult to collect, but are extremely important in assessing how and when the climate-induced changes measured in more-accessible parts of the world’s oceans reach the Antarctic ice sheet.
Dr. Katherine Leonard is a researcher at the WSL Institute for Snow and Avalanche Research (SLF) in Davos, Switzerland and also holds an appointment at the University of Colorado's Cooperative Institute for Research in Environmental Sciences in the USA. Her previous Antarctic field projects have included oceanographic surveys of the Ross, Amundsen, and Bellingshausen Seas, studies of iceberg calving from the Ross Ice Shelf, and research on sea ice and ice sheet snow and mass balance processes. She previously worked with BELISSIMA scientist Jean-Louis Tison during the International Polar Year "Ice Station Belgica" sea ice project in the Bellingshausen Sea, and with BELISSIMA scientist Frank Pattyn as a delegate to the IPCC WG1 expert meeting on Sea Level Rise and Ice Sheet Instabilities.
Picture: Dr Katherine Leonard taking a 820 m deep CTD measurment - © International Polar Foundation