Ocean temperatures dictate glacier calving

Ocean temperatures dictate glacier calving

Top image: Tunabreen calving. Photo: Doug Benn/UNIS

Arctic fjord temperatures control calving rates at tidewater glaciers in Svalbard. A direct link between ocean temperatures and glacier calving rates has now been demonstrated by an international team of scientists from UNIS and the UK.

9 October 2015
Text: Eva Therese Jenssen / UNIS

One of the largest uncertainties in predicting sea level rise in a warming climate is the iceberg calving rate: the rate at which marine-terminating glaciers will discharge ice to the ocean.

Glaciers, and the ice-sheets that feed them, cover 10% of the Earth surface and lock-in 75% of the Earth’s fresh water. As the Earth’s atmosphere and oceans warm and ice melts, melt and runoff from this vast frozen reservoir will dominate future global sea level rise. Nowhere is ice-sheet behaviour more uncertain than where ice meets the ocean.

Calving rates vary strongly with ocean temperatures
In new research, published in Nature Communications, a team of researchers from the University Centre in Svalbard (UNIS), the University of Swansea and the Scottish Association for Marine Science (SAMS) show that in Svalbard it is the temperature of seawater in contact with the glacier that controls the rate of ice loss.

In a process known as ‘melt undercut calving’ the ocean erodes the glacier beneath the waterline, causing the ice above to simply crumble into the fjord under its own weight. This process dominates glacier discharge in Svalbard and may well do so elsewhere. Wherever melt-undercut calving is the dominant process, future predictions of ice discharge in a warming climate can be made using models of ocean temperature and circulation.

The scientists looked at three Svalbard glaciers with different flow rates: Kronebreen in Kongsfjorden, Tunabreen in Tempelfjorden and Aavatsmarkbreen in Forlandsundet.

They used an unusually dense series of very high resolution images from the TerraSAR-X satellite. Data at a resolution of two metres, acquired every 11 days for 18 months, was analysed to measure both the seasonal advance and retreat of the glacier front, and the speed at which ice was replenished from further up the glacier. Water temperature at 20-60 meters depth was measured by a moored instrument in the adjacent fjord.

The velocity map shows the speed of Kronebreen over an 11-day period. Figure: Adrian Luckman et.al.

The velocity map shows the speed of Kronebreen over an 11-day period. Figure: Adrian Luckman et.al.

Huge advance in understanding glacier-ocean dynamics
– We now understand for the first time what controls iceberg calving rates in Svalbard, says Professor Adrian Luckman from Swansea University and UNIS, lead author of the paper.

– We anticipate that deep fjord water temperatures also control ice discharge in many other Arctic glacier settings, he concludes.

The research was conducted as part of the CRIOS project (Calving Rates and Impact on Sea Level), funded by the ConocoPhillips/Lundin Northern Area Program.

– This detailed satellite record has allowed us to make a huge advance in understanding how calving glaciers react to ocean warming, says UNIS Professor Doug Benn, leader of the CRIOS project.

Kronebreen terminates in Kongsfjorden, Svalbard. Photo: Nick Hulton/UNIS

Kronebreen terminates in Kongsfjorden, Svalbard. Photo: Nick Hulton/UNIS

Interdisciplinary research effort
According to Dr. Finlo Cottier from the Scottish Association for Marine Science, this study resolves the debate over the competing influences of ocean versus air temperature on glacial calving.

For over a decade oceanographers Professor Frank Nilsen from UNIS together with Dr. Cottier and Professor Inall from SAMS, have investigated processes by which coastal water is exchanged, and how warm ocean waters are drawn towards the glaciers.

The new findings offer insight into how warm ocean currents influence glacier response and allow for more accurate prediction of future marine-terminating glacier melt in a warming world.

Luckman, A., Benn, D.I., Cottier, F., Bevan, S., Nilsen, F., Inall, M.: Calving rates at tidewater glaciers vary strongly with ocean temperature. Nature Communications. doi 10.1038/ncomms9566 (2015).

Author contacts:
Professor Adrian Luckman: a.luckman@swansea.ac.uk

Professor Doug Benn: dib2@st-andrews.ac.uk

Professor Frank Nilsen: frank.nilsen@unis.no