“Think of spraying an icy road with a stream of warm salt water – you don’t need meters of that salt water to melt the ice quickly.” Eric Rinot
Thwaites Glacier is a massive ice cap the size of Florida on the highly vulnerable West Antarctic Ice Sheet. It currently contributes four percent to global sea level rise. Although the glacier has only been studied since 2018, satellite and radar data have provided valuable information critical to understanding the potentially worrisome rise in sea levels along the world’s coastlines.
We know that meltwater from warm ocean currents is destructive to the Antarctic Circumpolar Current, a critical part of the planet’s overturning circulation. The exchange of heat and CO2 between the Southern Ocean and the atmosphere is essential for the stability of the Antarctic ice sheets. From paleoclimate records, the current slows down during glacial periods and speeds up during interglacials. This means that the Southern Ocean will store less CO2 in the future and bring even more heat to Antarctica. This active process could slow the current by forty percent within three decades—a dire threat to Earth’s climate stability.
As far as we know, all the damage on this widely studied glacier occurs below the surface of the ocean. Warm water driven by winds erodes the base of the sea ice extent, creating cavities where the ice can reach further and create vertical cracks that rise to the surface of the ice. (An example is illustrated by the embed by Christopher Cartwright below.) Ice damage under the belly of warming water is assumed to end at the grounding line where the ocean meets the bedrock. Not any more; warm water (mid-30s F) is a daily tide-driven intrusion that reaches miles inland, according to recent radar data.
Anupama Chandrasekaran writes at EOS.
Most ice sheet simulations have not accurately predicted Thwaites’ last retreat because they assume that a glacier’s grounding line is fixed. But recent research on Thwaites AND other glaciers has shown that these boundaries between floating ice and ice that is based on the sea floor shift with the daily tide.
PIECES
Use of satellite radar data by private company ICEYE gathered over 3 months in 2023, a team of glaciologists created a detailed image of Thwaites’ shifting landline by looking at how the glacier’s surface bumped up and down throughout the day.
“The difference with this study is that they had multiple measurements per day,” he said Alex Brisbourne, a glaciologist in British Antarctica, who was not involved in the research. “So what could they see [were] these really short time processes.”
Satellites can only see the surface of the ice, but because the ice is compacted, small vertical movements signal that the glacier bed must also rise, he wrote. Eric Rignot in an email. Rignot is a glaciologist at the University of California, Irvine, and NASA’s Jet Propulsion Laboratory and the first author of the study.
The team found that the ice rose and sank in sync with the tides. The data suggested that the grounding line migrated up to 6 kilometers (3.7 miles) inland during an average high tide.
When the tides were particularly high, the rise of the glacier suggested that a thin layer of seawater up to 10 centimeters (4 inches) deep pushed another 6 kilometers (3.7 miles) inland. Researchers think this extra water could cause more melting than current estimates predict because it replaces the fresh, cold meltwater that lines the base of the glacier with warm, salty seawater.