MADRID, 14 (EUROPA PRESS)
Iceberg calving and subsequent drift are driving glacial melt to mix with warmer groundwater, exacerbating the retreat of Greenland's glaciers.
An international research team, led by Dominik Gräff, a glacier researcher at the University of Washington and affiliated with the Chair of Glaciology at ETH Zurich, has used fiber optic technology to measure for the first time how the impact of ice calving and subsequent drift drives the mixing of glacial melt with warmer groundwater.
"Warmer water increases seawater-induced melt erosion and erodes the base of the vertical ice wall at the glacier edge. This, in turn, amplifies glacier calving and the resulting mass loss from ice sheets," said Andreas Vieli, professor at the Department of Geography at UZH and co-author of the study, in a statement. These new insights into the dynamics of glacier ice and seawater appear on the cover of the latest issue of Nature.
As part of the GreenFjord project, UZH and the University of Greenland (UW) joined other Swiss institutions to conduct an extensive field study on glacier calving dynamics. Researchers deployed a ten-kilometer-long fiber optic cable on the seafloor across the fjord of the Eqalorutsit Kangilliit Sermiat glacier. This large, fast-flowing glacier in southern Greenland releases around 3.6 km of ice into the sea each year—almost three times the volume of the Rhône Glacier at the Furka Mountain Pass in Switzerland.
The researchers used a technology called Distributed Acoustic Sensing (DAS), which detects ground motion by monitoring cable tension caused by ice cracks, falling ice blocks, ocean waves, or temperature changes. "This allows us to measure the different types of waves generated after iceberg calving," says lead author Dominik Gräff, who completed his PhD at ETH Zurich.
After the initial impact, surface waves, known as calving-induced tsunamis, spread across the fjord, initially mixing the upper layers of water. Since the seawater in Greenland's fjords is warmer and denser than glacial meltwater, it sinks to the bottom.
UNDERWATER WAVES THAT ATTRACT WARMER WATER
But the researchers also observed other waves propagating between the density layers long after the impact, when the surface had calmed down. These underwater waves, which can reach the height of a skyscraper, are not visible from the surface, but they prolong the mixing of waters, bringing a constant supply of warmer water to the surface. This process increases melting and erosion at the glacier's edge and drives ice calving. "The fiber optic cable allowed us to measure this incredible calving multiplication effect, something that wasn't possible before," says Gräff. The data collected will help document iceberg calving processes and improve our understanding of the accelerated loss of ice sheets.
Scientists have long recognized the importance of seawater and calving dynamics. However, measuring relevant processes in situ presents considerable challenges, as the large number of icebergs along fjords poses a constant risk of ice chunks falling. Furthermore, conventional satellite-based remote sensing methods cannot penetrate below the water surface, where interactions between glaciers and seawater occur. "Our previous measurements have often only scratched the surface, so a new approach was needed," says Andreas Vieli.
