Loss of mass from ice sheets contributes to rising sea level. To understand the contributions of ice-sheets to sea level rise we must understand the spatial and temporal variability of ocean-driven melting, which has accelerated over recent decades. Dutrieux and colleagues used observations and results from numerical modeling to show the case of Pine Island Glacier in the Amundsen Sea in west Antarctica. Since 1973 the glacier has thinned, with increased oceanic melting of its ice shelf believed to be the cause. During the summer of 2012, however, oceanic melting decreased by 50%, the lowest on record. Intrusions to the shelf of modified warm (2-4oC) and saline Circumpolar Deep Water provides heat to the base of the ice shelf (below 200 m), increasing basal melt. Abnormal ocean conditions in 2012 were partially due to a shift in the wind regime the previous year, which decreased the flux of CDW onto the continental shelf. This wind anomaly was attributed to a weak convection in the western tropical Pacific associated with a La Nina event (2011).
Another factor playing a role in the distribution of heat over the continental shelf is the bottom topography. The presence of a ridge in front of the grounding line of Pine Island Glacier enhances vertical mixing which contributes to basal melting. The results from this study point to the importance of understanding the temporal and spatial modes of atmospheric variability and local topography to the predictions of ice-sheet contributions to sea level rise.
Pierre Dutrieux, Jan De Rydt, Adrian Jenkins, Paul R. Holland, Ho Kyung Ha, Sang Hoon Lee, Eric J. Steig, Qinghua Ding, E. Povl Abrahamsen, Michael Schröder. 2013. Strong sensitivity of Pine Island Ice-shelf melting to climatic variability. Science DOI:10.1126/science.1244341