Pine Island Glacier is melting faster than previously thought, scientists have discovered. The disturbing discovery came from recruiting seals as research assistants, attaching ocean monitoring devices to them to record the state of the waters through which they swim.
The catastrophic melting of Arctic sea ice has been closely monitored by satellites, and we have a good idea of the bad things happening to Greenland. The state of Antarctic ice is much more contested, however, with many important steps in the process occurring in places that are exceptionally hard to study.
Some particular important, but hard to access, locations are far beneath the surface where seawater meets the leading edge of glaciers. Melting here is natural, but how fast it happens is one of the most crucial factors determining the fate of coastal cities and other low-lying areas this century. Hundreds of meters beneath the surface of the world’s most remote and icy ocean, that is not easy to measure, particularly in winter.
Seals, however, love these waters so Dr Yixi Zheng of the University of East Anglia figured they could lend a flipper. After all, it’s their ecosystem at stake as much as anyone's. Zheng and colleagues attached devices to measure water temperature and salinity to seven elephant seals and seven Weddell seals living in the Amundsen Sea.
In Communications: Earth and Environment, Zheng reports the news the seals brought back is worrying, although far from the final word. Pine Island Glacier is a large West Antarctic glacier, known as probably the fastest melting on the continent. However, Zheng and colleagues found even these observations may underestimate the amount of meltwater it is producing.
Some 450 meters (1,500 feet) beneath the ocean surface Zheng found a layer of relatively fresh water that has apparently recently melted off the glacier’s lower portions. Columns dot the ocean where this meltwater rises to near the surface, but the deep melt layer spreads further from the glacier’s front than the shallower layer of freshwater, something not previously suspected. That’s not entirely a bad thing, as the rising meltwater brings nutrients with it. “The meltwater-related nutrient may boost the growth of marine planktons like algae,” Zheng said in a statement. That, in turn, could enhance the food-chain of the region as a whole.
Counterintuitively, however, the recently melted water is actually warmer than the seawater around it, which can be well below 0ºC, but kept liquid by salt. Consequently, rising meltwater disrupts the formation of sea ice and interferes with ocean circulation. The meltwater’s signature is easiest to detect in winter when there is no sunlight to produce similar effects at the upper levels, but the extreme conditions have obstructed investigations.
The team's observations were conducted over a single winter, so we don’t know if what they observed is part of a rising trend, an outlier, or something normal we were not aware of before.