The calving front of Eqalorutsit Kangilliit Sermiat in South Greenland. Researchers deployed the fiber optic cable several hundred meters from the glacier’s mouth. Credit: Dominik Gräff/University of Washington
As glaciers meet the sea and melt, massive blocks of ice ‘calve’ away and crash into the ocean. These awesome displays send tsunami-sized waves across the surface and leave powerful wakes as the ice bergs drift away.
Filling gaps in scientists’ understanding of how this process occurs is crucial to modelling future loss of ice sheets which will occur if ocean and air temperatures continue to increase due to global warming.
But getting up close to study glacier calving is a dangerous game.
Researchers have now shown that fibre-optic cables can be used to capture calving dynamics from a safer distance and discovered a previously unknown way in which tidewater glaciers interact with a warming ocean.
The bow of the field crew’s research vessel Adolf Jensen cutting through the ice of the fjord. Credit: Dominik Gräff/University of Washington
“We took the fibre to a glacier, and we measured this crazy calving multiplier effect that we never could have seen with simpler technology,” says Brad Lipovsky, assistant professor in Earth and space sciences at the University of Washington, USA, and co-author of a study presenting the findings in Nature.
“It’s the kind of thing we’ve just never been able to quantify before.”
In August 2023, the team dropped a 10km cable on the seafloor at the fjord of the Eqalorutsit Kangilliit Sermiat glacier in South Greenland.
“It has a diameter of 4mm and is armoured by 12 steel wire stands,” the authors write.
“By repeatedly sending laser pulses into fibre-optic cables and measuring the backscattered light as the pulses travel through the fibre, Distributed Acoustic Sensing (DAS) and Distributed Temperature Sensing (DTS) convert optical fibres into linear arrays of thousands of seismo-acoustic and temperature sensors.”
Julia Schmale, an assistant professor at Switzerland’s École Polytechnique Fédérale de Lausanne (left), and Manuela Köpfli, a University of Washington, USA, graduate student in earth and space science (right) unspool the fiber optic cable from a large drum, sending it down to the fjord-bottom to record data. Credit: Dominik Gräff/University of Washington
The technology measures changes in the way the light travels caused by vibrations, pressure and temperature fluctuations within the fibre.
For 21 days, the fibre-optic cable continuously detected seismic waves released from fracturing and iceberg detachment events and tsunamis, as well as seafloor temperatures and currents.
The researchers found that calving activity creates waves and currents which speeds up melting of the underwater portion of the glacier mass. Warm water stirred up by the waves eats away at the base of the glacier, which becomes top heavy and causes more overhanding portions to break off.
The researchers assume this process is happening at other tidewater glaciers across the world. They suggest it would have the most effect in areas with low current speeds where calving causes large perturbations in the water compared to how the ocean usually mixes.
University of Washington researcher Dominik Gräff (pictured on the left) and a crew member head for shore on a Zodiak boat. The research vessel Adolf Jensen floats on the fjord’s icy surface in the background and the calving front is visible on the left. Credit: Julia Schmale
“This result potentially explains why certain calving front models underestimate submarine melt by up to 2 orders of magnitude and should be investigated further,” they write.
Glacier calving is one of the key processes accelerating the rate at which the Greenland Ice Sheet is losing mass.
This melting has far-reaching consequences, including sea level rise – estimated to have contributed to rising sea levels by about 0.8mm each year since 2002 – global ocean currents – contributing to the slowdown of the Atlantic meridional overturning circulation (AMOC) – and local ecosystems.
“Our whole Earth system depends, at least in part, on these ice sheets,” says lead author and earth and space science researcher, Dr Dominik Gräff.
“It’s a fragile system, and if you disturb it even just a little bit, it could collapse. We need to understand the turning points, and this requires deep, process-based knowledge of glacial mass loss.”