Antarctic seals reveal alarming threats to disappearing glaciers

More Antarctic meltwater is emerging than previously known, changing the climate, preventing ice from forming and increasing marine productivity, according to new research from the University of Eastern Anglia (UEA).

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

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

The paper, “Observations based on seals at sea, reveals meltwater in the southeastern Amundsensee,” is published in the magazine today. Communication: Earth and Environment.

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

The surface meltwater provides heat to the surface that helps maintain areas of open seawater surrounded by sea ice, near glaciers, and can alter the melting rate of these brittle ice shelves. These findings provide important clues to better predict the future climate system and sea level rise.

Pine Island Glacier melts rapidly and carries the glacier meltwater to the ocean. Glacial meltwater is suspected to play a role in hydrography and distribution of sea ice, but little is known about it so far.

Yixi Zheng, a postgraduate researcher at the UEA’s School of Environmental Sciences, is the lead author of the study. She said: “The temperature and salinity of water change wherever glacier meltwater exists. Just as we are looking for a ‘fingerprint’ of glacier meltwater, we use temperature and salinity data to track the glacier meltwater.

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

“Because the glacier meltwater is warmer and fresher than the surrounding water, it is lighter than the surrounding water and is more likely to rise. It brings heat and nutrients such as iron to the near surface, which can melt the sea ice near “glaciers and increase the nutrient level near the surface. It increases the interactions between air and sea, and the meltwater-related nutrient can promote the growth of marine planktons such as algae.”

The winter processes revealed by the study are likely to be important in bringing nutrients to the layer surface before spring blooms, and in bringing heat to the surface to prevent sea ice from forming. This action helps to maintain the open water areas, called polynyas, in front of glaciers.

Many glaciers around Antarctica are rapidly thinning, mainly due to basal melting (ie melting that occurs at the interface between the ocean and the ice shelf glacier). The strongest melting was reported in West Antarctic glaciers, such as the Pine Island Glacier, where the research took place.

The amount of meltwater produced is small compared to the amounts of Antarctic shale seas, but it has an excessive impact on local circulation and climate.

The heat of the meltwater is likely to prevent the formation of sea ice, which causes sea ice to melt, thus increasing the extent of open water areas in front of glaciers.

The strong sea wind near the glacier front can also transport hot surface water further and further expand the area affected by meltwater. These enlarged polynia (open water areas surrounded by ice) can then lead to improved air-sea flooding and have further impact on the iceberg calving and melting of glaciers.

Seven southern elephant seals (Mirounga leonina) and seven Weddell seals (Leptonychotes weddellii) were captured and tagged with CTD Satellite Relayed Data Loggers around the Amundsen Sea in February 2014. The data were collected by marine mammals exploring the ocean pole to pole (MEOP). ). Researchers from the universities of Gothenburg and Rhode Island also contributed.

According to scientists, further research is needed. The study is based on one-year seal brand data from the Pine Island Glacier, so it can not be used to calculate trends over time or take into account the annual volatility such as the El Nino South oscillation, which could have a global impact not. water temperature.

The paper “On winter-based observations cause glacial meltwater to appear in the southeastern Amundsensee”, will be published in the magazine on 5 March 2021. Communication: Earth and Environment.

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