Faced with sea level rise that accompanies the progressive dissolution of polar ice due to global warming, scientists are diving into the ocean to discover how this melting occurs and enable some preventive (or mitigation) actions. One of these missions was revealed today, through two articles about the Thwaites Glacier, published in the journal Nature.
Thwaites is the name of a huge glacier in Antarctica that flows into the iconic Amundsen Sea. The MELT Project, a joint study by an international team made up of two groups, was carried out on this large glacier in the West Antarctic region — which is the size of the United Kingdom or the size of the state of Florida, in the United States of scientists, one British and one American.
A possible collapse of the Thwaites Glacier could raise sea levels to a magnitude that would have consequences for coastal populations in Europe and the world.
Peter Davis
Investigating one of the Antarctic glaciers that dramatically changes its constitution was imperative. In that case, much of the ice sheet is below sea level, making it susceptible to rapid ice loss, which could raise global sea levels by more than half a meter over the next few centuries.
Consulted by SINC, oceanographer Peter Davis, from British Antarctic Survey (BAS), and one of the authors of the work, explains: “The Thwaites Glacier, in West Antarctica, is buried below sea level, in a bedrock that deepens towards the interior and, therefore, subject to the potential risk of suffering a rapid and irreversible collapse.In his own words, such a collapse could raise sea levels by a magnitude that “would have substantial consequences for the coastal populations of Europe and the world”.
So, according to the scientist who led the British team, “we need to understand the processes that are driving the retreat of this glacier to be able to accurately predict the rate and extent of future sea level rise.”
Cracks, stairs and natural slides
Thwaites Glacier is one of the most rapidly changing ice and ocean systems. In fact, the part where the glacier connects to land, on the sea floor, has moved about 14 kilometers away since the late 1990s.
“Landline melting below the solid shelf (in the floating extent of the glacier) is a key process controlling the contribution of glaciers to future sea level rise,” argues Davis.
It was in this area bordering the glacier with the seafloor that the MELT team made the observations —more precisely, under the eastern Thwaites ice shelf—, to understand how the frozen layer interacts with the ocean in that critical sector.
The Great Glacier of West Antarctica is one of the most rapidly changing ice and ocean systems
There, scientists were able to witness the different processes that take place under the floating ice and verify that, although there is less dissolution than expected under much of the shelf, the ice dissolves more quickly in cracks and crevices, therefore, the glacier continues to retreat. Still, the results show that the current rate of melting is slower than many computer models currently estimate.
This is how the British researcher describes it: “We observed that flat ice surfaces reduce the rate of melting, but this increases strongly on inclined or vertical ice faces”.
Sometimes, according to the study, melting generates a ladder-shaped topography at the bottom of the platform, so that, in these strips, the ice melts more quickly.
The author points out that “these complex ice-ocean interactions are not currently incorporated into climate models, which increases our uncertainty in future sea level projections”.
With the help of an underwater robot
Nature magazine articles provide a clearer picture of the changes transforming the glacier from below. To assess these mutations, each of the teams took a different approach to the edge of the glacier that connects with the land.
Ice melts faster in crevasses and sloped surfaces, so the glacier keeps retreating
Davis describes it this way: “By collaborating with Britney Schmidt, we combined our experience in accessing the ocean, through drilling on the eastern Thwaites Ice Shelf, with the technology contained in her underwater vehicle, known as the Icefin. This has given us an unprecedented ability to explore the complex ice-ocean interactions that occur in that land connection sector.”
At the end of 2019, BAS scientists took measurements in the ocean, through a well 600 meters deep, about two kilometers from the ground line, thanks to a hot water drill. These were compared with melt rate observations made at five other locations below the shelf.
In a period that lasted about nine months, they were able to verify that, in that sector, the sea water became warmer and with a higher saline concentration, but the base of the ice melted, on average, between 2 and 5 meters per year (a value lower than the expected in the previous model).
Hole through which the underwater robot was introduced under the ice sheet. /Team BAS
About these discoveries, the author points out that the results were “a surprise” and, however, the glacier is still “in trouble”. If an ice shelf and glacier “are in balance,” the continent’s ice will compensate for what melts or breaks off, but scientists have found that even though the ice is melting at a slower rate than estimated, “there is still a rapid retreat of the glacier”, which makes them predict that “it doesn’t take much to unbalance it”.
In turn, Dr. Britney Schmidt, from Cornell University, in the United States, and her team implanted the robot through the drilling carried out by the British group. In this way, they were able to access these deep areas of connection to the earth that were previously almost impossible to inspect.
Thanks to Icefin’s observations, they discovered, under the ice shelf, that these ladder-like formations (or terraces and cliffs) melt quickly. And this is particularly striking in the case of cracks, which create a funnel effect through which heat and salt are channeled, widening them.
These complex ice-ocean interactions are not currently incorporated into climate models.
Peter Davis
In the presentation of the joint work, Schmidt, main author of the second study, sums it up as follows: “These new ways of observing the glacier allow us to understand that it is not just a question of knowing how much is melting, but how and where the melting takes place in these very hot parts of Antarctica.”
The scientist concludes: “we see rifts, and probably terraces, through warming glaciers such as Thwaites. Warm water is seeping in through these fissures, helping to erode the glacier at its weakest points.”
References:
P.Davis et al. “Suppressed basal melt in the eastern Thwaites Glacier landfill zone“. Nature (2023).
B. Schmidt et al. “Heterogeneous melt near the Thwaites Glacier grounding line”. Nature (2023)