January 23, 2017: FB1-Seminar

11:00 h, Lecture Hall, Düsternbrooker Weg 20

Abstract:

The ocean is thought to play an important role in modulating the mass balance of the Greenland Ice Sheet by delivering heat to the marine-terminating outlet glaciers around Greenland. The largest of three outlet glaciers draining the Northeast Greenland Ice Stream (the latter covering 15% of Greenland’s surface) is Nioghalvfjerdsfjorden Glacier (79 North Glacier). Historical observations in the 1990s had shown that warm waters of Atlantic origin are present in the subglacial cavity below the 80 km long floating ice tongue of the 79 North Glacier. They are thought cause strong basal melt near the glacier’s grounding line.  

A sizeable amount of the warm and saline waters carried northward along the eastern boundary of the Nordic Seas by the Norwegian Atlantic Current – West Spitsbergen Current system does not enter the Arctic Ocean but recirculates in Fram Strait. These waters are subducted below the cold and fresh East Greenland current, and move southward along the shelf of Northeast Greenland.  

In order to understand how Atlantic waters supply heat towards the 79 North Glacier, we analyse historic and recent bathymetric, hydrographic, and velocity observations in Fram Strait and on the shelf of Northeast Greenland. It is shown that a trough system allows the penetration of the subsurface waters Atlantic Waters across the shelf edge and the 300 km wide shelf toward the cavity of the 79 North Glacier. Consistently, based on recent velocity measurements a subsurface flow of warm Atlantic waters towards the glacier is demonstrated. Our most recent measurements revealed a density plume in the vicinity of the glacier calving front causing a rapid inflow of Atlantic waters warmer than 1°C into the subglacial cavity.  

Our analysis of the available historical observations further suggests a coherent decadal increase in Atlantic water temperatures both in Fram Strait and along the entire trough system on the Northeast Greenland shelf. A warming-induced increase of basal melting may explain the observed thinning of the glacier tongue throughout the last 15 years.

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