A squad of seals living off the coast of West Antarctica has provided scientists with data that could help to improve estimates of future sea-level rise.
Researchers equipped the roly-poly marine mammals with sensors that measured temperature and salinity in the Amundsen Sea. This remote and understudied patch of ocean could be accelerating the melt of the West Antarctic ice sheet, so year-round information on water conditions is key to predicting the ice sheet’s contribution to the world’s rising oceans.
The study, published on 14 May in Geophysical Research Letters1, reveals that a deep-water current known as the Circumpolar Deep Water (CDW) is bigger, warmer and saltier in the winter months than in summer.
The current is a warm, salty doughnut of water that circles Antarctica at depths of 500-1,000 metres. In the Amundsen Sea, this warm band of water is thought to be accelerating the melt of the West Antarctic ice sheet, which if lost entirely could raise sea levels by 3.2 metres.
The Amundsen Sea hosts two of the biggest and fastest-retreating glaciers in Antarctica: the Thwaites and Pine Island glaciers. These hulking masses of snow and ice would deliver an estimated 40% of the West Antarctic ice sheet to its watery grave.
The latest study provides the first detailed data on the CDW in this region. “In these very remote regions, we often only have a snapshot of what the conditions are like. This is one of the first times we’ve started to get the bigger picture that shows variability in this system,” says Andrew Thompson, a physical oceanographer at the California Institute of Technology in Pasadena.
Despite the Amundsen Sea’s influence on the West Antarctic ice sheet, studies of the region have been hampered by the harsh Antarctic environment. Researchers could gather limited information year-round by bolting instruments called moorings to the sea floor, or conduct more-complex experiments in the summer, when the sea ice is thin enough for ships to crunch through.
The patchy data that resulted made it hard to determine whether the CDW in the Amundsen Sea was warmer or wider at certain times of year. To fill this gap, researchers from the University of East Anglia in Norwich, UK, and the University of Stockholm linked up with the Sea Mammal Research Unit at the University of St Andrews, UK.
The team glued sensors to the heads of seven southern elephant seals (Mirounga leonina) and seven Weddell seals (Leptonychotes weddellii) to probe an area of 150,000 square kilometres for 9 months, including the harsh winter. In that time, the seals recorded more than 10,000 distinct measurements. The previous two decades of research with moorings and ship-based instruments produced 2,000.
“Seals are the perfect assistant to gather this data. They’re there the whole year round, and they can stay in places with horrible weather that ships can’t possibly be in,” says Helen Mallett, a physical oceanographer at the University of East Anglia, and the study’s first author.
The new data could help hone the accuracy of climate models that attempt to project how quickly the West Antarctic ice sheet will melt. “The goal is to understand how the Antarctic Ocean interacts with the ice shelves and contributes to sea level rise,” says Yoshihiro Nakayama of NASA’s Jet Propulsion Laboratory in Pasadena. “The biggest problem is that we don’t have enough data.”
Last month, Britain’s Natural Environment Research Council and the US National Science Foundation announced the International Thwaites Glacier Collaboration. The 5-year, £20-million (US$25-million) project to study the receding Thwaites Glacier will send Mallett and her co-authors back to the Amundsen Sea in 2019 to extend their data set with another group of tech-savvy seals.
Mallett, H. K. W. et al. Geophys. Res. Lett. https://doi.org/10.1029/2018GL077430 (2018).