Strong Sensitivity of Pine Island Ice-Shelf Melting to Climatic Variability

Cold Glacier Growth Pine Island Glacier in Antarctica has thinned significantly during the last two decades and has provided a measurable contribution to sea-level rise as a result. Both glacier dynamics and climate are thought to be responsible for thinning, but exactly how they influence the glacier are incompletely known. Dutrieux et al. (p. 174, published online 2 January) provide another layer of detail to our understanding of the process through observations of ocean temperatures in the surrounding waters. The thermocline adjacent in the sea adjacent to the glacier calving front (where ice is discharged) lowered by 250 meters in the austral summer of 2012. This change exposed the bottom of the ice shelf to colder surface waters rather than to the warmer, deeper layer, thereby reducing heat transfer from the ocean to the overlying ice and decreasing basal melting of the ice by more than 50% compared to 2010. Those 2012 ocean conditions were partly caused by a strong La Niña event, thus illustrating how important atmospheric variability is for regulating how the Antarctic Ice Sheet responds to climate change. Colder surface ocean waters decreased the rate of melting under the Pine Island Glacier ice shelf in 2012. Pine Island Glacier has thinned and accelerated over recent decades, significantly contributing to global sea-level rise. Increased oceanic melting of its ice shelf is thought to have triggered those changes. Observations and numerical modeling reveal large fluctuations in the ocean heat available in the adjacent bay and enhanced sensitivity of ice-shelf melting to water temperatures at intermediate depth, as a seabed ridge blocks the deepest and warmest waters from reaching the thickest ice. Oceanic melting decreased by 50% between January 2010 and 2012, with ocean conditions in 2012 partly attributable to atmospheric forcing associated with a strong La Niña event. Both atmospheric variability and local ice shelf and seabed geometry play fundamental roles in determining the response of the Antarctic Ice Sheet to climate.

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