Antarctic sea ice may be melting faster than expected

A new model developed by Caltech and JPL researchers suggests that Antarctica’s ice shelves could be melting at an accelerated rate, which could eventually contributing to faster sea level rise. The model accounts for an often-overlooked narrow ocean current along the Antarctic coast and simulates the rate at which flowing fresh water melts from ice shelves. , can trap dense, warm ocean water at the base of the ice, causing it to heat up and melt even further.

The study has was conducted in the lab of Andy Thompson, professor of environmental science and engineering, and appears in the journal Science Advances on 12 August.

Ice shelves are outcrops of the Antarctic ice sheet, found where ice juts out from the land and floats above the ocean. The shelves, which are each several hundred meters thick, act as a protective buffer for continental ice, preventing the entire ice sheet from flowing into the ocean (which would dramatically raise global sea levels) . However, warming of the atmosphere and oceans caused by climate change is increasing the rate at which these ice shelves are melting, threatening their ability to hold back the flow of the ice sheet into the ocean.

“If this mechanism we are studying is active in the real world, it may mean that the rates of sea ice melt are 20 to 40 % higher than predicted by global climate models, which generally cannot simulate these strong currents near the Antarctic coast. “, says Thompson.

In this study, led by principal investigator Mar Flexas, the researchers focused on one area of ​​Antarctica: the West Antarctic Peninsula (WAP) . Antarctica is roughly disc-shaped except where the WAP exceeds high polar latitudes and in lower, warmer latitudes. It is here that Antarctica is experiencing the most dramatic changes due to climate change. The team has already deployed autonomous vehicles to this region, and scientists have used data from instrumented elephant seals to measure the temperature and salinity of water and ice.

The team’s model takes into account the narrow Antarctic Coastal Current that runs counter-clockwise around the entire Antarctic continent, a current that many climate models don’t not include auto it is so small.

“The large world climate models do not include this coastal current, auto it is very narrow – only about 20 kilometers in size, whereas most climate models only capture streams of 100 kilometers or more,” says Flexas. “It is therefore possible that these models do not very accurately represent future melting rates.”

The model illustrates how fresh water that melts from the ice at the WAP is carried by the coastal current and transported across the continent. The less dense fresh water moves rapidly near the ocean floor and traps the relatively warm salt ocean water against the underside of the ice shelves. This then causes the ice shelves to melt from below. In this way, increased meltwater at the WAP may propagate global warming through the coastal current, which in turn may also accelerate melting even on West Antarctic ice shelves thousands of kilometers away. of the peninsula. This remote warming mechanism could partly explain why the loss of volume of the West Antarctic ice shelves has accelerated in recent decades.

“ There are aspects of the climate system that we are still discovering,” Thompson says. “As we progress in our ability to model interactions between the ocean, ice shelves and atmosphere, we are able to make more accurate predictions with better constraints on uncertainty. . We may need to revise some of the predictions of sea level rise over the next few decades or the next century – this is work we will do in the future.”

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