Thwaites Glacier findings reveal clues about Antarctic ice melt

Driving the news: Two new studies published Wednesday in the journal Nature provide some of the most detailed results gleaned from a $50 million, five-year international research campaign between the U.S. and the U.K., aimed at shedding light on the factors influencing Thwaites' future.

• Specifically, scientists were interested in investigating the glacier's grounding zone, which is where the ice meets the sea and becomes a floating ice shelf.

State of play: Thwaites is unique in that as one travels inland from the grounding line, the ice rests on bedrock that dips below sea level.

• This makes this region especially susceptible to extensive and potentially rapid melting since there is no hill or steep upward slope to slow or stop the ice's retreat.

Zoom in: Scientists used remotely operated submersibles, including a craft known as Icefin, inserted into a 2,000-foot hole drilled into the ice, along with other means to obtain data on the water coming into contact with Thwaites' grounding line and floating ice shelf.

• The submersible captured data on ocean temperatures and salinity, among other important variables.
• Abundant new information was also gleaned about the topography of the bedrock underlying the glacier, including at the grounding line.

Of note: Thwaites may have already begun a rapid and irreversible ice loss that will add about two feet of sea level rise this century.

Between the lines: One of the studies found that water that is well above freezing is located near the grounding zone, but not all of it is reaching the base of the ice.

• This suggests that rapid grounding line retreat, which continues to be observed here, could be tied to modest melt rates, and that this pace of retreat is likely to continue.
• Should the even warmer water reach the base of the ice, retreat would likely quicken, and it may be much higher in other parts of the glacier this study did not examine.
• "The [melt] rates found at the particular location were low and yet this is a place that retreated fast," study coauthor Eric Rignot of UC Irvine told Axios via email.
• "This means we should be worried, very worried for the other places where the melt [rates are] high and the retreat is high. The system is very sensitive to the ocean, more than we thought."

The intrigue: The second study looked at the topography of the glacier's grounding line, and found the ice shelf melting faster where there are steep slopes and crevasses carved into the ice.

• Specifically, the ice slopes greater than 30 degrees were estimated to contribute to 27% of the total areal melt rate of the study region, despite comprising just 9% of the portion of the ice base that was surveyed.

What they're saying: "These types of observations are incredibly difficult to make, but they are so important to informing the modeling community about how indeed the vulnerable parts of the ice sheets are melting," coauthor Peter Washam of Cornell University told Axios.

• "Overall, these papers don’t really change my level of worry about Thwaites collapse or not," said Richard Alley, a climate scientist at Penn State University who was not involved in the new research.  
• "But, the papers increase my optimism that we can make sense of this incredibly difficult and important system, and improve our ability to project what it may do in the future." 

What's next: Rignot noted that these studies were the result of a massive scientific effort, of the sort that is rarely mounted. However, the costs versus benefits of such campaigns in Antarctica favor doing them more often, he said.

• "The research will serve to protect cities from sea level rise, with adaptation costs in the billions of dollars for any major city, and trillions of dollars worldwide," Rignot said.