Researchers have generally thought that the East Antarctic Ice sheet has remained relatively stable despite global warming. But this is not the case, according to a recent study published in Science Advances. Chad Greene and a team of researchers discovered that the Totten, the largest glacier in East Antarctica, is melting. Shockingly, if the Totten Glacier were to melt entirely, it could raise sea levels by 11 feet.
“For the past decade, my research group at the University of Texas Institute for Geophysics has flown airborne campaigns over Totten to characterize its sensitivities, because Totten drains a massive portion of the East Antarctic Ice Sheet, about 550,000 km2, or ~3.5 m sea level rise in a complete collapse scenario,” Greene told Glacierhub. “That’s about as much ice as all the rapidly-changing glaciers of West Antarctica combined.”
The team’s project to study the Totten was a collaboration between the University of Texas at Austin, the University of Tasmania, and the Antarctic Climate and Ecosystems Cooperative Research Centre. Fernando Paolo, another member of the team, has shown that for long-term observations, Totten clearly thickens and thins on an interannual basis. So, the outstanding question was, what causes these interannual changes? What force is powerful enough to affect this massive system?
Using satellite data from 2001 to 2006, the researchers noted the increased movement of the Totten Ice Shelf toward the ocean. The ice shelf represents the floating portion of the glacier. In a pervious interview, Greene describes this phenomenon as “pancake batter that’s piled up and spreads toward the edges under its own weight.” Melting, whether from the surface or the bottom in contact with the ocean, tends to thin the ice sheet and increase the rate of flow outward.
This increased melt is also confirmed by the International Collaboration for Exploration of the Cryosphere through Aerogeophysical Profiling (ICECAP) Project, a collaboration between U.S., British and Australian Antarctic researchers that has been mapping the East Antarctic ice sheet. They have identified an area near Totten Glacier that is thinning with lowering surface heights at a rate of approximately 2m per year.
“Many forces act on Totten. We used satellite images to track Totten’s movements and found that on the interannual timescale, variability in glacier speed is influenced primarily by winds over the ocean nearby,” Greene told Glacierhub. When winds over the Southern Ocean intensify, warm water is pulled up from the deep ocean onto the continental shelf, creating the hot spot. “It’s like when you blow across a hot bowl of soup and little bits of noodles from the bottom begin to swirl around and rise to the top,” he added. This comparison suggests the dynamic nature of the thermocline, which refers to the region under water where temperature changes more rapidly with depth. The wind-driven upwelling raises the thermocline on the continental shelf and dunks the underside of Totten Ice Shelf in a warm water bath.
The wind drives the thermocline, bringing warm water toward the coast of the Totten Glacier, and circulates below through submarine canyons, causing it to melt from below. “The temperature difference experienced by a parcel of ice that’s suddenly exposed to this warm water is only a couple of degrees Celsius, but remember that bit of ice may be more accustomed to water that’s just 0.2 degrees above freezing–so a 2 degrees shock is about a 10 fold increase in melting power,” Greene said. This kickstarts a positive feedback mechanism that is self-reinforcing. More inland ice is exposed to the warm waters when the coastal layers of ice melt, and when these landlocked ice drain into the ocean, sea-level rise is certain.
Greene thinks of the Totten Glacier as “the sleeping giant because it’s huge and has been seen as insensitive to changes in its environment.” However, his team’s findings have shed light on what has caused the Totten’s rates of melting to vary over the years. With climate change expected to intensify the winds over the Southern Ocean in the next 100 years, the Totten Glacier will likely be impacted. This is groundbreaking news, since people often relate melting glaciers to increases in air or ocean temperatures, when, in fact, winds are actually sufficient.
“Some basal melt is a healthy part of a steady-state mass balance for Totten, so observations of melt are not shocking or cause for alarm,” Greene told GlacierHub. However, he added that his team showed an interesting sensitivity that changes in wind over the ocean get transmitted to the ice sheet. Greenhouse gases such as carbon dioxide have amplifying effects on Antarctic winds, deciding the fate of glaciers just by deciding the movement of warm water. “Of course, that has a gloom-and-doom component, but it’s also an interesting scientific curiosity–now we see how CO2 can lead to sea level rise without warming up the air and melting ice from above, and without even warming up the ocean, but just by moving heat around within the ocean,” he said.
What is the melting of just another glacier? If it is the Totten Glacier, it could mean another 11 feet of sea level increase.