"Past and future dynamics of the Greenland Ice Sheet: what is the ocean hiding?" is a research project based at The Geological Survey of Denmark and Greenland (GEUS) in Copenhagen (DK). The project is funded by a Villum Foundation grant (PI Camilla S. Andresen).
The Greenland Ice Sheet has gained massive attention in recent years due to a sudden increase in mass loss at the onset of this century. A significant part of this mass loss has been attributed to increased ice discharge at the margin through iceberg calving from marine-terminating outlet glaciers. However, due to the lack of instrumental data beyond the past 20–30 years, it is difficult to evaluate if this was an outstanding event, or if it was part of a recurring phenomenon acting on inter-annual, inter-decadal, or centennial timescales.
Sediment cores have been retrieved during cruises conducted in 2009–2014 from fjords around Greenland. The main objective of this VILLUM Foundation funded project is to extend the record of glacier variability and oceanographic changes beyond the past 20–30 years by analysing marine sediment cores from the vicinity of marine Greenland glacier termini. By comparing a large set of glacier and ocean reconstructions from different settings around Greenland we investigate the influence of oceanographic changes on glacier variability, the timescales involved and gain understanding of the role of the glaciological and bathymetrical setting on outlet glacier changes. These extended climatological and glaciological time series can to be used for calibration of a simple glacier flow model. This will enable a relatively more reliable prediction of future mass loss and changes in sea level.
To address the problem of assessing the respective influences of climate setting and glacier- and fjord morphology on outlet glacier variability, we analyse sediment cores retrieved in recent years from several glacier-fjord-shelf systems (see map).
Different earth system variables (i.e. calving, current strength, melt water production, oceanographic changes) on various timescales may be evaluated depending on the precise core site setting. In the vicinity of the glacier margin, the sedimentation in the fjord is mainly characterised by high rates of suspension settling from turbid overflow plumes deposited as laminated mud and subsequently often redistributed with tidal and wind-induced currents. On the basis of a transect of cores, variability in circulation and current strength up to 150 years back in time can be documented. Further down-fjord from the glacier margin the sediment is mainly produced by debris rafted from icebergs exiting the fjord; the flux of sand here is thus the combined effect from iceberg calving and sediment content in icebergs, where the latter can be modulated by climatic processes. Increased inflow of warm subsurface waters into deeper fjords may increase the calving rates of outlet glaciers. Using proxies such as alkenone UK37' and foraminifera assemblage changes we will document the interaction between warm subsurface waters and glacier calving during the Holocene on inter-annual, multi-decadal and centennial timescales. On the shelf, sediment is mainly composed of ice rafted debris, mud in suspension from (glacial) runoff and biogenic material from microorganisms such as calcareous nannoplankton, foraminifera, diatoms, dinoflagellate cysts and their chemical finger prints the biomarkers (alkenones and IP25).
The extended glaciological time series will serve as a tool for tuning an advanced numerical glacier model. Calibration of the model is carried out by running the model for the time period for which the extended glaciological time series has been constructed. Here, the reconstructed ocean, air, and sea ice variability will be used as fixed input parameters and the model parameters can be adjusted. Once the model demonstrates the ability to capture the observed glaciological variations (simulate the recorded changes), we will have increased confidence in the reliability of its prognostic assessments.
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