High in the southern Andes, a huge ice mass known as the Southern Patagonia Ice Field straddles the border between Argentina and Chile. The ice, which spans approximately 12,500 square kilometers, feeds more than 60 major glaciers that flow into the Pacific Ocean or into freshwater lakes. In a new study, Sugiyama et al. reveal the unique interactions between ice and water that characterize glacier-fed lakes in this region.
Glaciers that flow into lakes are known as lake-calving glaciers. The number of these glaciers worldwide is growing due to the formation of new lakes in front of retreating ice, but to date, most studies of ice-water interactions have focused on glaciers that flow into the sea. A better understanding of lake-calving glaciers, however, could improve predictions of sea level rise and other consequences of global warming.
The team studied lakes at the front of three large glaciers fed by the Southern Patagonia Ice Field: Glaciar Perito Moreno, Glaciar Upsala, and Glaciar Viedma. For each glacier, the researchers used boat-mounted equipment to measure lake water temperature, sediment concentration (turbidity), and bathymetry.
The scientists found significant differences between the behavior of these glaciers and ocean-calving ones. When a glacier ends in the sea, meltwater discharge from the glacier bed rises because it is less dense than the surrounding seawater. Warm seawater flows to the front of the glacier and promotes more melting. However, the scientists found that in the Patagonian lakes, cold, turbid meltwater lingers in the depths because of its high sediment concentration. Without an influx of warmer surface water, deep glacier melting is likely limited in these lakes.
The measurements also revealed that the Patagonian lakes contain an upper layer of relatively warm water mixed by surface winds. This layer, which reaches to a depth of about 180 meters, delivers heat to shallower portions of the submerged glaciers.
This study is the first to explore the thermal structure of glacier-fed lakes in Patagonia. Further studies are needed to clarify the processes that affect melting at the ice-water boundary of other lake-calving glaciers. (Journal of Geophysical Research: Earth Surface, https://doi.org/10.1002/2016JF004084, 2016)
—Sarah Stanley, Freelance Writer