“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 Reno
Thwaites Glacier is a massive ice cap the size of Florida in the highly vulnerable West Antarctic Ice Sheet. It currently contributes four percent to global sea level rise. Although the glacier has only been surveyed since 2018, satellite and radar data have provided valuable information critical to understanding the alarming potential sea level rise along the world’s coasts.
We know that meltwater from warm ocean currents is disruptive 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 data, the current slows during glacial periods and accelerates during interglacial periods. This would mean that the Southern Ocean would store less CO2 in the future and bring even more heat to the Antarctic. This active process could slow the flow by forty percent within three decades—a terrifying threat to Earth’s climate stability.
As far as we know, all the damage on this widely studied glacier occurs below the ocean surface. Warm water driven by winds erodes the base of the sea ice extent, creating cavities where the ice can reach farther and creating vertical cracks that rise to the surface of the ice. (One example is illustrated by the embed by Christopher Cartwright below.) Damage from warming water under the belly of the ice is assumed to end at the grounding line, where the ocean meets the bedrock. No longer; warm water (mid-30s F) is a daily tidal intrusion that reaches miles inland, according to recent radar data.
Anupama Chandrasekaran writes at EOS.
Most ice sheet simulations have not accurately predicted Thwaites’ recent retreat because they assume the glacier’s ground line is fixed. But recent research by Thwaites and other glaciers showed that these boundaries between floating ice and ice that is grounded on the seafloor shift with the daily tide.
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Use of satellite radar data by private company ICEYE collected over 3 months in 2023, a team of glaciologists created a detailed image of the changing Thwaites grounding line by watching how the surface of the glacier bobbed up and down throughout the day.
“The difference with this study is that they had multiple measurements per day,” he said Alex Brisbane, a glaciologist with the British Antarctic Survey who was not involved in the research. “So what could they see [were] these really short 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 be rising, it says Eric Rignot in an email. Rigneault is a glaciologist at the University of California, Irvine and NASA’s Jet Propulsion Laboratory and first author of the study.
The team found that the ice rises and sinks in sync with the tides. The data suggest that the grounding line migrated up to 6 kilometers (3.7 mi) inland during an average high tide.
When tides were particularly high, the glacier’s uplift meant that a thin layer of seawater up to 10 centimeters (4 in) deep pushed a further 6 kilometers (3.7 mi) inland. The researchers believe that this extra water may be causing more melting than current estimates predict, as it replaces the cold meltwater that covers the base of the glacier with warmer, saltier seawater.
