Zurich/Seattle, WA—An international research team led by the University of Zurich (UZH) and the University of Washington (UW) has, for the first time, used fiber-optic technology to discover a critical underwater mechanism that rapidly accelerates the melting and retreat of Greenland’s massive ice sheet.
The discovery, highlighted on the cover of Nature, reveals that the impact of large ice blocks calving into the ocean generates internal underwater waves that mix warm seawater with cold meltwater for extended periods, significantly amplifying glacier melt and erosion.
The Calving Multiplier Effect
Iceberg calving, the process where ice splits from a glacier’s front and falls into the ocean, is a major contributor to ice loss. The research focused on the Eqalorutsit Kangilliit Sermiat glacier in southern Greenland, which releases about 3.6 km 3 of ice into the ocean each year.
As lead author Dominik Gräff explains, when an iceberg crashes into the water, it generates surface waves (calving-induced tsunamis) and, more importantly, internal underwater waves. Because the seawater in Greenland’s fjords is warmer and denser than meltwater, the mixing process brings this warm water upward toward the glacier’s vertical ice face.
“The warmer water increases seawater-induced melt erosion and eats away at the base of the vertical wall of ice at the glacier’s edge,” explains UZH Professor Andreas Vieli, co-author and leader of the GreenFjord project’s Cryosphere cluster. “This, in turn, amplifies glacier calving and the associated mass loss from ice sheets.”
These internal underwater waves, which can reach heights comparable to skyscrapers, continue to mix the water long after the surface has calmed, creating a persistent “calving multiplier effect” that was previously impossible to measure.
Distributed Acoustic Sensing (DAS) Breakthrough
Collecting detailed measurements of ice-seawater interaction has always been extremely difficult due to the constant hazards from falling ice and the inability of satellites to see below the surface.
To overcome this, the researchers deployed a ten-kilometer-long fiber-optic cable on the seafloor across the fjord. They used a method called Distributed Acoustic Sensing (DAS), which detects tiny vibrations along the cable caused by events like falling ice, crevasses, and the generated waves.
“The fiber-optic cable allowed us to measure this incredible calving multiplier effect, which wasn’t possible before,” said Gräff.
The data gathered provides crucial new insights that will support future models to better document calving events and understand the rapid decline of ice sheets.
Fragile System, Global Consequences
The Greenland ice sheet, which covers an area about 40 times larger than Switzerland, holds enough ice to raise global sea levels by about seven meters if it were to melt completely.
The researchers emphasize that the retreat of calving glaciers has far-reaching consequences:
- Sea-Level Rise: Direct contribution to global sea-level rise.
- Ocean Currents: The large volumes of meltwater flowing into the ocean can disrupt major currents like the Gulf Stream, potentially affecting Europe’s climate.
- Ecosystems: The retreat also affects the sensitive ecosystems within Greenland’s fjords.
“Our entire Earth system depends, at least in part, on these ice sheets. It’s a fragile system that could collapse if temperatures rise too high,” warned Gräff.