Unveiling Hidden Histories: Antarctic Subglacial Rocks Unmask Unexpected Past

The exploration camp on Thwaites Glacier served as a base for the team engaged in drilling operations. Credit: Greg Balco (Berkeley Geochronology Center). An intriguing discovery by researchers from the International Thwaites Glacier Collaboration pointed out that the West Antarctic Ice Sheet was thinner in the past but managed to recover, indicating potential reversibility of glacial retreat. They derived this insight from rock samples that reflected a past where the ice near Thwaites Glacier was at least 35 meters thinner than present in the last 5000 years and took no less than 3000 years to regain its present size. This extensive recovery period raises concerns considering the impending climate change’s impact on sea-level rise.

The West Antarctic Ice Sheet is diminishing, with a host of glaciers in the region retreating and melting at a distressingly rapid pace. But, this wasn’t always the scenario as per the recent research published in The Cryosphere last month. Scientists from the International Thwaites Glacier Collaboration (ITGC), inclusive of two researchers from the British Antarctic Survey (BAS), discovered that the ice sheet near Thwaites Glacier was thinner a few thousand years ago than it is currently. This unexpected revelation demonstrates that the regional glaciers had the capacity to recover from previous reductions.

Rising sea levels pose a significant risk to millions residing in low-lying coastal areas worldwide due to potential flooding. Melting Antarctic ice significantly contributes to the uncertainty in predicting the rate and magnitude of future sea level rise. Thwaites Glacier and its immediate neighbor presently contribute significantly to the Antarctic’s input to sea-level rise. To anticipate this critical glacier’s response to forthcoming climate changes, scientists require insights into its behavior under various climate conditions and over extended periods. As satellite observations only cover a few decades, it’s crucial to delve into the geological records for such data.

The rock cores retrieved from Thwaites for analysis were transported back to the laboratory. Credit: Keir Nichols (Imperial College London). As Jonathan Adams, co-author and Ph.D. student at BAS, states, “To gain a better understanding of how the Antarctic Ice Sheet could change in the future, we study the history of glaciers like Thwaites. To discern what happened beyond the 5000-year mark, we need to examine rocks currently concealed beneath the ice sheet as the surface rock records cease around then.”

Using specialized drills that could penetrate both ice and the underlying rock, the team extracted rock samples from deep beneath the ice sheet near Thwaites Glacier. These samples were then analyzed for specific atoms that form when rocks are exposed to radiation from outer space. If these rocks are covered by ice, the formation of these atoms ceases. Therefore, their presence indicates instances when the ice sheet was smaller than its current size.

Keir Nichols, a glacial geologist from Imperial College London and a lead author of the study, points out, “This was a colossal team effort. Several of us spent weeks doing fieldwork in a remote part of Antarctica, while others devoted thousands of hours in the lab analyzing the rocks we collected. The atoms we measured are present only in tiny quantities in these rocks, so we were pushing the boundaries of current capabilities, with no surety of success. We are thrilled that this is the first study to disclose the recent history of an ice sheet using bedrock collected directly beneath it.”

The team unearthed the fact that the rocks they sampled were not perpetually covered by ice. Their measurements demonstrated that the ice near Thwaites Glacier was at least 35 meters thinner during the past 5000 years than it is currently. Moreover, their models indicated that its subsequent expansion to its present size took a minimum of 3000 years.

Related links:

• International Thwaites Glacier Collaboration
• British Antarctic Survey
• The Cryosphere
• Berkeley Geochronology Center
• Imperial College London