How does the sensitive ice of West Antarctica react to increased temperatures? Is there a risk of irreversible ice melting there? A 228 meter long sediment core from West Antarctica could now provide answers to these questions. It is the longest and furthest-reaching drill core from this region. It was won by an international team at the junction of the Ross Ice Shelf and the West Antarctic Ice Sheet during a drilling expedition as part of the SWAIS2C project. Initial assessments of the sediment core have already provided evidence that the Ross Sea must have been ice-free repeatedly over the last 23 million years. More detailed analyzes now have to clarify when that happened and what the causes were.
West Antarctica’s ice is particularly vulnerable to warming from current climate change. Antarctica is losing more ice in this area than anywhere else. If this continues, this melt could even become irreversible. The ice sheet is supported on one side by the Ross Ice Shelf – the largest floating ice mass in the world. This acts like a brake block and inhibits the flow of glaciers and ice streams towards the ocean. If this brake is removed, the thaw in West Antarctica could accelerate rapidly and become unstoppable. If this were to be the case, it would have significant consequences for sea levels, as the West Antarctic ice sheet contains enough ice to cause global sea levels to rise by up to five meters. However, it is still unclear when and at what temperatures there is a risk of such a tipping over of the West Antarctic ice sheet.
523 meters through the ice and 228 meters deep into the sediment
A sediment core obtained by an international research team as part of the SWAIS2C (Sensitivity of the West Antarctic Ice Sheet to 2°C of Warming) project can now provide more information. A German scientist was also present during the drilling in the ice. On its drilling expedition, the team traveled around 700 kilometers from the nearest polar station, New Zealand’s Scott Base, to the edge of the Ross Ice Shelf. There, at the transition area between the ice shelf and the West Antarctic ice sheet, the drilling team spent almost ten weeks in tents on the ice. The drilling equipment had already been brought there using snow groomers. In order to access the sediment deep beneath the ice, the researchers first had to use hot water to melt a hole through the 523 meter thick ice. They then used a special drill to remove the sediment cores from the subsoil in sections. “Research under extreme Antarctic conditions and at the limits of what is technically feasible is a particular challenge,” says Arne Ulfers from the LIAG Institute for Applied Geophysics in Hanover.
But the team was successful: they drilled a 228 meter long sediment core from the subsurface of this critical transition zone in West Antarctica. The sediments preserved in the drill core date back to around 23 million years ago. They can therefore provide valuable information about how this area has changed during past climate changes. Because during this time there were several periods in which the earth was warmer and richer in CO2 than it is today. “We are thrilled to have finally obtained such a record core, which will give us extremely important information about how the West Antarctic ice sheet in the Ross Sea sector reacted at times that were warmer and more CO2 richer than today,” says Johann Klages, German co-coordinator of the SWAIS2C project and geoscientist at the Alfred Wegener Institute in Bremerhaven.
There were ice-free times in the Ross Sea
The first, still preliminary, investigations into the freshly drilled sediment sections have already provided initial clues. This is because they show a variety of different sediment types, from fine-grained sediment to more solid material with embedded large stones. In some layers, shell fragments and remains of marine organisms that require light to survive can be seen. This suggests that the Ross Sea was not covered by ice shelves at these times. “The first preliminary indications that there were ice-free phases in the past are extremely exciting and scientifically promising,” says project scientist Denise Kulhanek from the Christian Albrechts University of Kiel (CAU). “Extensive further research is now needed to understand the climatic conditions under which these were formed.” The research team first brought the sediment cores obtained from the Ross Ice Shelf to the Scott Research Base in New Zealand. From there they are then transported to New Zealand to be analyzed in more detail in various laboratories around the world.
“These records will give us important insights into how the West Antarctic Ice Sheet and Ross Ice Shelf will respond to temperatures above two degrees Celsius,” says Huw Horgan, SWAIS2C co-chief scientist from Victoria University of Wellington in New Zealand. Klages adds: “Together with drill cores that we want to obtain in the Amundsen Sea next year with the research vessel Polarstern and a seabed drilling rig, these new and extremely difficult to obtain archives will hopefully be able to answer the question of when and under what conditions the West Antarctic ice sheet will disappear – i.e. key data for testing and fundamentally improving the reliability of the latest climate models.”
Source: SWAIS2C