What is causing the rapid retreat of the Thwaites Glacier?

The Thwaites Glacier is one of the fastest changing glaciers in Antarctica, with its grounding zone – the point where it meets the seafloor – retreating 14 kilometers since the 1990s. Since much of this glacier’s ice sheet lies below the sea level and is susceptible to rapid, irreversible loss, global sea levels could rise by over half a meter within centuries if melting continues at such rates.

However, according to two new recent studies published in the journal Nature, although melting has increased beneath the floating ice shelf, the current rate of melting is slower than several computer models have estimated. 

By collecting data from ocean measurements through deep boreholes at six different locations underneath the ice shelf over a nine-month period, a team of researchers led by the British Antarctic Survey (BAS) and Cornell University has found that the rapid retreat of this glacier is driven by different processes under the ice shelf. According to the scientists, while melting beneath much of the ice shelf is weaker than expected, melting in cracks and crevices is much faster.

“Our results are a surprise but the glacier is still in trouble,” said Peter Davis, an oceanographer at BAS and lead author of one of the studies. “If an ice shelf and a glacier is in balance, the ice coming off the continent will match the amount of ice being lost through melting and iceberg calving. What we have found is that despite small amounts of melting there is still rapid glacier retreat, so it seems that it doesn’t take a lot to push the glacier out of balance.”

Thus, although the vertical melting along the base of the ice shelf was less than expected, melting along sloped ice in cracks and terraces is much higher and could be a major factor in ice loss across this massive glacier, particularly as large rifts are progressing along the ice shelf and may become the primary trigger for ice shelf collapse.

“These new ways of observing the glacier allow us to understand that it’s not just how much melting is happening, but how and where it is happening that matters in these very warm parts of Antarctica. We see crevasses, and probably terraces, across warming glaciers like Thwaites. Warm water is getting into the cracks, helping wear down the glacier at its weakest points,” explained Britney Schmidt, an associate professor of Planetary Science at Cornell and lead author of the second study. 

“Our results demonstrate that the canonical model of ice-shelf basal melting used to generate sea-level projections cannot reproduce observed melt rates beneath this critically important glacier, and that rapid and possibly unstable grounding-line retreat may be associated with relatively modest basal melt rates,” the experts concluded.

—-

By Andrei Ionescu, Earth.com Staff Writer

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.