This award supports a research cruise to perform geologic studies in the area under and surrounding the former Larsen B ice shelf, on the Antarctic Peninsula. The ice shelf's disintegration in 2002 coupled with the unique marine geology of the area make it possible to understand the conditions leading to ice shelf collapse. Bellwethers of climate change that reflect both oceanographic and atmospheric conditions, ice shelves also hold back glacial flow in key areas of the polar regions. Their collapse results in glacial surging and could cause rapid rise in global sea levels. This project characterizes the Larsen ice shelf's history and conditions leading to its collapse by determining: 1) the size of the Larsen B during warmer climates and higher sea levels back to the Eemian interglacial, 125,000 years ago; 2) the configuration of the Antarctic Peninsula ice sheet during the LGM and its subsequent retreat; 3) the causes of the Larsen B's stability through the Holocene, during which other shelves have come and gone; 4) the controls on the dynamics of ice shelf margins, especially the roles of surface melting and oceanic processes, and 5) the changes in sediment flux, both biogenic and lithogenic, after large ice shelf breakup.
The broader impacts include graduate and undergraduate education through research projects and workshops; outreach to the general public through a television documentary and websites, and international collaboration with scientists from Belgium, Spain, Argentina, Canada, Germany and the UK. The work also has important societal relevance. Improving our understanding of how ice shelves behave in a warming world will improve models of sea level rise.
The project is supported under NSF's International Polar Year (IPY) research emphasis area on "Understanding Environmental Change in Polar Regions".
In the popular literature and scientific press, the break-up of the Larsen Ice Shelf on the eastern side of the Antarctic Peninsula, vividly captured by satellite imagery in early 2002, came to represent a portrait of the catastrophic effects of global warming. The LARISSA project was designed to address both the cause(s) and impacts of ice shelf loss, in a polar marine setting. The project utilized a comprehensive, interdisciplinary approach to study the Larsen Ice Shelf system as a model and as a predictor of the likely continent-wide changes that Antarctic ice shelves will experience in response to the modern warming trend. Our initial focus was on the Larsen B region, as a representation of the evolving Antarctic system in miniature, with the recognition that it encompassed a scale that allowed relevant processes and interconnections to be observed. The project combined modern observations of glacial, oceanic, and biological dynamics, coupled with ice core and sedimentary records, to give a long-term perspective of climate and system response. Field work was conducted during a total of four field seasons, and included work aboard both US and Korean icebreakers, and with helicopter and fixed wing aircraft support. As a consequence of unexpectedly difficult sea ice conditions in the Larsen, we expanded our field program to our backup sites along the western Antarctic Peninsula. During our first cruise aboard the US icebreaker the NB Palmer, we accessed the eastern side of the Peninsula via helicopter support over the mountainous spine of the Peninsula, where we were successful in deploying both GPS units, to detect terrestrial uplift following ice loss, and AMIGOS stations (Automated Meteorology – Ice/Indigenous species – Geophysics Observation System) to monitor ice and weather conditions. We also collected rock samples for exposure age dating, in order to place modern ice loss into the context of ice loss since the last glacial maximum. Ship-based science conducted during all four cruises succeeded in sampling a broad latitudinal spread of fjord systems, and transects of sites from the inner to outer continental shelf. At these sites (1) we conducted comprehensive biological surveys of both the upper ocean phytoplankton and benthic biota to evaluate biological response to climate change, (2) we collected physical oceanographic data to monitor changing oceanic conditions, (3) we deployed moored instruments to collect year long oceanographic measurements and data on sediment flux, (4) we mapped previously uncharted regions of the sea floor and (5) we recovered marine sediment cores as archives of changing environmental conditions since the last glacial maximum. During our first field season, the ice core group successfully recovered a 445.6 meter core from the glacial ice on the Bruce Plateau; the core is the longest yet recovered from this region, and has sub-annual resolution in its upper section. Major findings include 1) confirmation that the loss of the Larsen B Ice Shelf in 2002 was an event unique to modern warming; the ice shelf existed since it formed over 10,000 years ago at the end of the last glacial maximum, 2) the distinctive sea floor signature of overlying ice shelf collapse in the form of greatly increased sedimentation of ice-rafted debris at sites close to the ice margin, and widespread biologically-produced sediment as a consequence of photosynthesis in the newly ice shelf free bays, and 3) a cohesive record of post-glacial climate change, observed in both the marine sediment and ice core records, including a clear response to the Little Ice Age, between approximately 700 – 100 years ago. This International Polar Year (IPY) project successfully addressed key IPY objectives through this unprecedented opportunity to explore the polar environment and the changes now taking place there, with a team of international scientists and technicians that included biologists, glaciologists, oceanographers, marine geologists, and Quaternary geologists. We hope that our combined observational database will provide benchmarks and data to be used by modelers to predict future behavior of Antarctica’s ice shelves and tributary glaciers, and associated upper-ocean and benthic habitats. The lessons learned in this IPY effort also include an enhanced understanding of the logistical complexities of combining marine and terrestrial research, and the demands and requirements for successful helicopter operations from polar research vessels.
