The climate implications of sea ice
As polar sea ice plays a major role in climate, predictions of climate change rely on information about sea ice conditions from the geological past. Such information is difficult to obtain, but certain biomarker chemicals originating from algae serve as an effective proxy for investigating past sea ice conditions. The EU-funded ICEPROXY (Novel lipid biomarkers from polar ice: Climatic and ecological applications) project studied lipids from unicellular sea ice algae. Lipids are a group of fatty molecules having several key functions in cellular metabolism, in addition to a structural role in cell membranes. Ice lipids are abundant, robust and long lasting, and were obtained from Arctic and Antarctic sediment cores. The consortium assessed and verified the chemicals' value as indicators of sea ice conditions over at least the last 10 000 years. Initial analysis confirmed the robustness and algal origins of the lipids. Calibration against historical or other sea ice proxy information revealed new subtleties in the ice record. Reconstruction of 30 000 years of ice conditions in the Fram Strait in Antarctica revealed that the area experienced an abrupt warming around 14 000 years ago. The situation meant ice-free waters during summer. Shortly after, the region cooled again and returned to permanent sea ice conditions. The changes affected primary production and caused widespread ecological decline. Similar sediment analyses from the North Icelandic Shelf revealed sudden changes in ocean surface conditions over the last thousand years. The changes resulted from a series of equatorial volcanic eruptions. The events caused significant ocean cooling, followed by rebound to warmer, ice-free conditions due to subsurface heat build-up. Multi-proxy study of recent Antarctic iceberg calving showed that such events occurred every 80-90 years for the last few centuries. The events were always accompanied by an increase in sea ice concentrations and decrease in the dense water formation. Analysis showed that intensification of the Southern Annular Mode (resulting from human-caused ozone depletion) also produces icier conditions. The ICEPROXY project's new proxy method for determining previous sea ice conditions help with predictions of climate change and with assessment of impact on wildlife.
Keywords
Sea ice, sediments, climate change, biomarker, algae, ICEPROXY, ecological
