Polar News

Seals Help Predict Ice Melt in Antarctica’s Remote and Inaccessible Regions

Two species of seal have helped scientists collect important temperature and salinity data in a remote and often inaccessible part of the Antarctic.

For 200 years, difficult ice conditions have prevented explorers from entering the remote Amundsen Sea off West Antarctica. This region has experienced some of the most rapid ice loss in the Antarctic, contributing to around 10% of the observed sea-level rise around the world. It wasn’t until 1994 that scientists could begin mapping the ocean structure and circulation, revealing that the reach of the warm Circumpolar Deep Water (CDW) extends to the continental shelf.

Environmental scientists at the University of East Anglia (UEA) have been investigating ways of studying the CDW - a warm, salty layer of deep water derived from a mixture of all the world’s ocean and forms a key component of the Antarctic Circumpolar Current. By measuring the temperature, salinity, and depth of the CDW as it moves towards the ice sheet, scientists hope the data will help climate change modelers make more accurate predictions about how rapidly the Antarctic ice sheet is melting.

Some scientists estimate that as the ice in West Antarctica melts, sea levels could rise by up to 3.2 meters with much of the water draining through two glaciers -- Pine Island Glacier and Thwaites Glacier. But estimates of future sea level rise vary, and scientists need year-round observations to assess and improve vital climate change models.

While gathering data in the summer is relatively straightforward, the Amundsen Sea is inaccessible to ships during the winter because a thick blanket of sea ice blocks access. Scientists have been able to retrieve some information in a few fixed locations by installing a moored string of sensors anchored to the seafloor. The presence of large icebergs in the area, however, means that the sensors cannot measure near the sea surface without the risk of collision.

To address this, the UEA team set up a collaboration with the Sea Mammal Research Unit at the University of St Andrews who was interested in recording the feeding behaviors of seals in the region. The expedition built on an idea originally suggested by scientists at the British Antarctic Survey when they became aware of a large elephant seal haulout on islands near the Pine Island Glacier.

EMBED 1 matt palmer 204708 unsplashIn February 2014, the team - funded by the Natural Environment Research Council's Ice Sheet Stability Research Program (iSTAR) - tagged seven southern elephant seals and seven Weddell seals with devices that can send information via satellite. Measurements of the warmth and saltiness of the water were sent by the seals as they moved around the area and dived through the water column to the seabed as they hunt for food.

Throughout the Antarctic winter, over a period of nine months, the team collected data from more than 10,000 dives over an area of around 150,000 square kilometers. The seals continued to send back signals until they molted, and the devices dropped off.

"We knew very little about what to expect from this research since this is the first time that data has been collected in this way in this area," says Helen Mallett, who led the study at UEA. "We were able to collect much more information from the seals than all the previous ship-based surveys in the area combined, and it was clear that, at least during the seasons we observed, there were substantial differences in temperature between the seasons."

Analyzing the findings published in Geophysical Research Letters, the researchers discovered that not only is the layer of CDW thicker in winter, it is also warmer and saltier than during summer months. This suggests that there is likely to be more melting of the ice sheets during the winter period. The temperature differences were less marked closer to one of the glaciers in a region called Pine Island Bay, possibly because ocean currents recirculate the water.

Mallet continued, "Although more will need to be done to measure these differences over a number of years, it's clear that enlisting seals to collect this kind of ocean data will offer useful insights for climate change modelers who are attempting to predict how fast sea levels will rise."

The data will also be useful to marine biologists as it will provide a new understanding of the foraging behavior of seals in the Amundsen Sea, and how that might be affected by climate change, as well as commercial fisheries.

The UEA and St Andrews team are heading back to the Amundsen Sea in 2019 to enlist the help of another group of seals to monitor this remote region as part of the recently announced International Thwaites Glacier Collaboration.

‘Variation in the Distribution and Properties of Circumpolar Deep Water in the Eastern Amundsen Sea, on Seasonal Timescales, Using Seal-Borne Tags’ is published in Geophysical Research Letters on Tuesday, May 15.

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