Antarctic seals reveal disturbing threats to disappearing glaciers

According to new research from the University of East Anglia (UEA), more Antarctic meltwater is surfacing than was previously known, altering the climate, preventing sea ice from forming and increasing marine productivity.

For the first time, researchers were able to obtain observations of glacial meltwater at full depth in winter, using instruments attached to the heads of seals living near the Pine Island Glacier in the remote Amundsen Sea. , west of Antarctica.

The harsh environmental conditions of Antarctica limit the use of most traditional observing systems, such as ships and airplanes, especially in winter. But oceanographers working with biologists have used data collected by tagged seals to measure the temperature and salinity of the water.

The article, “Observations based on winter seals reveal surface of glacial meltwater in south-eastern Amundsen Sea,” is published today in the journal Communications: Earth and environment.

The researchers found a highly variable meltwater distribution with two meltwater-rich layers – one in the top 250 meters and the other about 450 meters deep – connected by scattered columns rich in meltwater. melting. The hydrographic signature of meltwater is clearest in winter, when its presence can be unambiguously mapped; this analysis is only possible in winter.

Surface meltwater provides near-surface heat that helps maintain areas of open seawater surrounded by sea ice, close to glaciers, and can alter the rate of melting of these fragile platforms. of ice. These results offer important clues to better predict the future climate system and sea level rise.

The Pine Island Glacier is melting rapidly, exporting glacial meltwater to the ocean. Glacial meltwater is thought to play a role in the hydrography and distribution of sea ice, but so far little is known about it.

Yixi Zheng, a postgraduate researcher at the UEA School of Environmental Sciences, is the lead author of the study. She said, “Water temperature and salinity change wherever glacial meltwater exists. Just like looking for a ‘footprint’ of glacial meltwater, we use temperature and salinity data to track glacial meltwater.

“The distribution of glacial meltwater is very uneven. It does not mix well with ambient water, but flows along two layers rich in meltwater in the upper 250 meters and about 450 meters, connected by columns rich in meltwater.

“Because glacial melt water is warmer and cooler than ambient water, it is lighter than ambient water and more likely to rise. It brings heat and nutrients such as iron to the near surface, which can melt sea ice near glaciers and increase the level of nutrients near the surface. This improves air-sea interactions, and nutrients bound to meltwater can stimulate the growth of marine planktons like algae. “

The winter processes revealed by the study are probably important in bringing nutrients to the layer near the surface before spring flowering and in bringing heat to the surface to prevent the formation of sea ice. maintain areas of open water, called polynyas, in front of glaciers.

Many glaciers around Antarctica are thinning rapidly, primarily due to basal melt (that is, the melt that occurs at the interface between the ocean and the ice pack glacier). The strongest melt was reported in glaciers in western Antarctica such as the Pine Island Glacier, where the research took place.

The volume of meltwater produced is small compared to the volumes of the Antarctic Shelf seas, but it is believed to exert a disproportionate influence on regional circulation and climate.

The heat from meltwater is likely to prevent the formation of sea ice, allowing sea ice to melt and thereby increasing the extent of open water areas in front of glaciers.

The strong offshore wind near the glacier front can also carry the warm water further near the surface and expand the region influenced by the meltwater. These enlarged polynyas (areas of open water surrounded by ice) can then lead to increased air-sea flows and have other impacts on the calving of icebergs and the melting of glaciers.

Seven southern elephant seals (Mirounga leonina) and seven Weddell seals (Leptonychotes weddellii) were captured and tagged with CTD satellite relay data loggers around the Amundsen Sea in February 2014. Data was collected by marine mammals exploring the oceans from pole to pole (MEOP). Researchers from the Universities of Gothenburg and Rhode Island also contributed.

Scientists say more research is needed. The study was based on a year of seal tag data from the Pine Island Glacier, so it cannot be used to calculate trends over time or take into account year-to-year variability such as the El Nino Oscillation. – southern, which can affect the water temperature.

The article, “Observations based on winter seals reveal surface of glacial meltwater in south-eastern Amundsen Sea,” is published on March 5, 2021 in the journal Communications: Earth and environment.

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