Global warming: New threat to Antarctic ice shelves

Warming air temps likely to trigger a chain reaction that could undermine stability of glaciers

Disintegration of ice shelves in East Antarctica could result in a spiraling increase in sea levels. PHOTO BY BOB BERWYN.

By Summit Voice

SUMMIT COUNTY — While British researchers recently showed how warming ocean currents are melting ice sheets in West Antarctica, other areas may also be susceptible rapid and potentially catastrophic disintegration — especially the Filchner-Ronne Ice Shelf fringing the Weddell Sea.

Rising air temperatures in the region will break down a hydrological boundary of cold water, allowing warmer water to infiltrate beneath the ice. The model projects that huge masses of the as-yet stable ice shelf could become unstable and slide into the ocean in the next 50 to 60 years.

A new study by scientists with the Alfred Wegener Institute for Polar and Marine Research suggests the shelf could start to melt rapidly in this century and no longer act as a barrier for ice streams draining the Antarctic Ice Sheet.The findings, published the British science magazine Nature, refute widespread assumptions that ice shelves along the eastern side of the Antarctic Peninsula would not be affected by the direct influences of global warming due to the peripheral location of the Weddell Sea.

The chain reaction will be triggered by rising air temperatures above the southeastern Weddell Sea, the researchers said.

“Our models show that the warmer air will lead to the currently solid sea ice in the southern Weddell Sea becoming thinner and therefore more fragile and mobile in a few decades,” said Frank Kauker. If this happens, fundamental transport processes will change, Kauker explained.

“This will mean that a hydrographic front in the southern Weddell Sea will disappear which has so far prevented warm water from getting under the ice shelf. According to our calculations, this protective barrier will disintegrate by the end of this century”, explains Hartmut Hellmer.

“We expect the greatest melting rates near the so-called grounding line, the zone in which the ice shelf settles on the sea floor at the transition to the glacier. At this point the Filchner-Ronne Ice Shelf is melting today at a rate of around 5 meters per year. By the turn of the next century the melt rates will rise to up to 50 meters per year,” said Hellmer’s colleague, Jürgen Determann.

Determann is investigating how the ice streams behind will react in the event of a melt of such enormous proportions.

One thing is obvious:

“Ice shelves are like corks in the bottles for the ice streams behind them. They reduce the ice flow because they lodge in bays everywhere and rest on islands. If, however, the ice shelves melt from below, they become so thin that the dragging surfaces become smaller and the ice behind them starts to move”, said Hartmut Hellmer.

“If the high melting rates are completely compensated by inland ice flow, this loss in mass would correspond to an additional rise in global sea level of 4.4 millimeters per year”, Determann said.

According to the latest estimates based on remote sensing data, global sea level rose for the period 2003-2010 at a rate of 1.5 millimeters per year due to melting of glaciers and ice shelves. Thermal expansion of the ocean adds another 1.7 millimeters per year.

The forecasts of the current study are based on independent calculations of the  several different ocean models. The scientists used the atmospheric projections of the British Met Office Hadley Centre in Exeter as forcing data. These included, for example, information on the future development of the wind and of the temperature in Antarctica.

Hellmer and his colleagues tried to validate their model by working backward to 1860, arriving at readouts closely matching the actual conditions of today.

The study was conducted as part of the EU-funded Ice2sea research program. This project brings together scientists from 24 leading research institutions of the European Union and from Chile, Norway and Iceland. Together, the scientists aim to decode interactions between ice and climate and facilitate more precise predictions about the effects of melting ice on sea level.



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