As the winds around Antarctica intensify with rising global temperatures, they're driving changes in the ocean that could speed up the flow of the massive Totten Glacier, which carries ice from East Antarctica into the ocean, adding to sea level rise, a new study says.
Along the coast, surface winds are projected to intensify over the century due to warming caused by increasing atmospheric greenhouse gas concentrations. The stronger winds can sweep aside a surface layer of very cold ocean water and enable warmer water from the depths to reach the base of the glacier's floating ice shelf and slowly eat away at the ice from below, the authors say.
The new study, published today in the journal Science Advances, used detailed ocean temperature records and 15 years of data on the movement of the Totten Glacier and ice shelf to show how the ice thins and accelerates in response to changes in the wind.
The expected changes in wind patterns during the 21st century, "due in part to human activity ... could drive Totten's retreat," the researchers concluded.
If the Totten Glacier were to melt completely, it could raise global sea level by 3.5 meters (11.4 feet) or more, they wrote.
Antarctica is covered by ice that's several miles thick in places. Glaciers form as gravity pulls the ice toward the sea. When the glaciers reach the ocean, they become massive floating ice shelves that slow the ocean-bound flow. The system was relatively stable until greenhouse gases and other pollution disrupted the climate system.
Scientists had documented a strengthening and poleward shift of the circumpolar westerly winds from the mid-1960s to the 1990s and attributed it to the ozone hole, said John King, science leader for atmosphere, ice and climate with the British Antarctic Survey. The ozone is recovering now, but King said climate models show that increasing greenhouse gas pollution will have a similar effect during the 21st century.
"The mechanisms behind the greenhouse gas forcing are complex. Certainly the subtropical highs move southwards as the westerlies move, but the ultimate cause is probably greater heating of the tropical and subtropical atmosphere relative to mid and high latitudes as the Southern Ocean is able to absorb much of the increased heating at these latitudes," King said.
The new study doesn't project a meltdown date for Totten Glacier, but it does mirror recent research from West Antarctica, said the study's lead author, Chad Greene, a climate researcher at the University of Texas Institute for Geophysics. In both regions, data suggest that intensifying winds push warmer water toward ice shelves.
There's been more research around the West Antarctic Ice Sheet, mainly because it's more accessible, so scientists have better data to work with when they warn of a possible large-scale meltdown that could raise sea level higher and more quickly than expected. Recent studies show long-term trends in thinning of the ice shelves there.
The new study on the Totten ice system is one of the few to start tracking similar dynamics in East Antarctica.
Some of the data on ocean temperatures near the ice came from an ocean probe that was deployed near the front of the Totten Glacier for about 14 months starting in 2015. It was the first time such an instrument had been used in that region simply because it's so hard to get to, Greene said. "The sea ice keeps ships from getting in there," he said. The 2015 Aurora Australis expedition mapped troughs along the sea floor that could channel warmer water from the depths to the ice shelf, and it detected water temperatures in some areas above the freezing point for the salt water.
"The new study shows warm water persists year-round and that variations in ocean temperature on the shelf are linked to changes in winds near the shelf break," said Australian climate researcher Esmee van Wijk, who analyzes ocean data from remote instruments and ships.
It's important to understand the processes at work because of the amount of ice that glaciers like Totten holds. And while nobody is talking about a quick meltdown scenario, people in low-lying areas, like Florida and Bangladesh, need to know if the ocean is going to rise several feet this century.
"East Antarctica has been ignored. People talk about it as the sleeping giant, in terms of potential sea level rise. The Totten Glacier is the one we should be trying to monitor," said David Gwyther, a climate scientist at the University of Tasmania, Australia who was part of the research team.