Climate science: Historic data suggests changing ocean currents melted glaciers at depth

The impact of the Atlantic Meridional Overturning Circulation (AMOC) - a system of ocean currents that includes the Gulf Stream - on the Greenland Ice Sheet 13,000 to 11,500 years ago is assessed in a study in Scientific Reports this week. The findings suggest that during this period (called the Younger Dryas), when atmospheric and sea surface temperatures dropped by up to 10 °C, changes in the AMOC may have warmed deeper waters, driving the erosion of Arctic glaciers in southeast Greenland and enhancing freshwater input into North Atlantic.

Arctic glaciers are projected to contribute between 19 and 30mm to sea level rise by 2200. However, these projections do not take into consideration oceanographic changes that may impact glaciers at subsurface levels. Eleanor Rainsley and colleagues used computer modelling based on sediment data to reconstruct interactions between the Greenland Ice Sheet and the AMOC during the Younger Dryas. The authors show that although terrestrial glaciers in Europe expanded widely during this period, marine glaciers lost a substantial amount of mass. This loss may have been driven by a strengthening of relatively warm, salty below-surface ocean currents that eroded glaciers at depth, despite cooler surface temperatures. The findings support the hypothesis that ocean circulation was more important than air temperature in southern Greenland during the Younger Dryas.

The authors suggest that Greenland meltwater may in the future affect North Atlantic circulation and increase subsurface temperatures in a way that could drive erosion of marine glaciers and further freshwater input into the North Atlantic. The findings highlight the importance of considering oceanographic, as well as atmospheric changes in projections of future sea level rise.