Estimate of submarine meltwater in northeast Greenland

From marine terminating glaciers along the boundary current into the Nordic Seas

Calving front of the floating glacier tongue of the 79 North Glacier.


Over the past decades the Greenland Ice Sheet has faced accelerated melting under warming climate conditions. The contributing processes involve surface melting, iceberg calving, and submarine melting through the contact of warming water with marine terminating glaciers. At the glacier front or even inside the cavity of floating glacier tongues, the heat of warm and saline Atlantic Water melts the floating ice shelf at its base. Besides the contribution of this submarine meltwater to sea level rise, this additional fresh water may alter the climate relevant ocean circulation.

Submarine meltwater can hardly be identified by its salinity far from the source regions. Therefore, we use own measurements of low soluble noble gases (helium He, and neon Ne) to identify, quantify and trace this freshwater component. 

Contacts: Dr. Dagmar Kieke, Prof. Dr. Monika Rhein, and Dr. Oliver Huhn

Figure 1. Map of eastern Greenland with available noble gas measurements. Polarstern expedition PS109 (2017, green) and Maria S. Merian expedition MSM85 (2019, yellow) were carried out within GROCE. The blue arrows indicate schematically the East Greenland Current and the circulation on the northeast Greenland shelf.

Figure 2. Geographical distribution of the SMW maximum near 79NG, on the shelf and (not significant) in western Fram Strait (SMW < 0.1%, i.e. below significance limit, displayed as black dots). The blue arrows indicate schematically the East Greenland Current and the circulation on the northeast Greenland shelf.

What was the main question you aimed to answer during the first project phase?

The major aim of this project was to answer the questions:

  1. How much submarine meltwater is formed in northeast Greenland, particularly from the floating ice tongue of the 79 North Glacier (79NG) over the continental shelf towards the boundary current?
  2. Which role does it play in the Nordic Seas and in the Irminger Sea for the ocean circulation? 

Which methods did you use to answer your research questions?

To identify and to quantify the fraction and distribution of submarine melt water, we use oceanic noble gas observations. The light and stable, low soluble noble gases helium (He) and neon (Ne) provide a unique tool for that. During the formation of a glacier from compacting snow, atmospheric air is trapped in bubbles and stored in the glacier ice. When this ice is melted again at depth or at the bottom of a floating ice tongue, these gases are completely dissolved in the melt water due to the increased hydrostatic pressure. This leads to an increase of 1280% He and 890% Ne in pure melt water.

What were your main results?

One of our major outcomes in the first project phase was the quantification of the submarine meltwater formation of the major outlet glacier in northeast Greenland (79 North Glacier, 79NG, Nioghalvfjerdsbrae) and the meltwater export using oceanic noble gas measurements.

  • Helium (He) and neon (Ne) serve to identify and quantify the distribution of submarine melt water (SMW) on the northeast Greenland shelf.
  • From He and Ne, we calculated a SMW formation rate of 14.5 ± 2.3 Gt per year, equivalent to a submarine melt rate of 8.6 ± 1.4 m per year of the 79NG. 
  • SMW fractions are present on the shelf, but dilute from 1.8% at the 79NG calving front to nonsignificant values in Fram Strait.
  • A surplus of Ne on most of the shelf region indicates that up to 10% of the original water mass had been transformed to sea ice.
     

What are your goals for GROCE-2?

  • How large are submarine meltwater fractions from Fram Strait downstream towards the Irminger Sea on the Greenland shelf, on the continental slope, and in the deep ocean?
  • Based on historic data, can we detect possible changes and estimate the order of meltwater discharge into the ocean interior?
  • Which role does submarine meltwater play in the ocean circulation in the Nordic Seas and in the Irminger Sea?
  • Which additional sources for freshwater can be identified, and which role do they play?