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> Forsiden > Natur og klima > Is og gletsjer > Past and future dynamics of the Greenland Ice Sheet

Past and future dynamics of the Greenland Ice Sheet: what is the ocean hiding?

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 funded project is to extend the record of glacier variability and oceanographic changes beyond the past 20-30 years by analyzing 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. By converting the glacier sediment archives into time series of specific ice mass changes we will obtain extended glaciological time series 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.

Researchers involved: Camilla S. Andresen (PI), Antoon Kuijpers, Niels Nørgaard-Pedersen (The National Geological Survey of Denmark and Greenland), Kurt Kjær and Kristian K. Kjeldsen (Geological Museum at the Museum of Natural History), Marit-Solveig Seidenkrantz and Nikolaj Krogh Larsen (University of Aarhus). International collaborators, amongst many others: John T. Andrews and Anne Jennings (INSTAAR), Tavi Murray (Swansea Uni.) Fiamma Straneo (WHOI), Dave Sutherland (Uni. Oregon) Kerim Nisancioglu (Bjerkness Centret). 

The project will engage two ph.d. students and three postdocs.

Project description

1. Reconstruction of ocean and outlet glacier changes on the basis of fjord sediment cores
To address the problem of assessing the respective influences of climate setting and glacier- and fjord morphology on outlet glacier variability, we analyze 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, implying that the more calving, the more icebergs exit the fjord, and the more coarse debris is deposited. Increased inflow of warm subsurface waters into deeper fjords may increase the calving rates of outlet glaciers. Using proxies such as alkenone UK37’, TEX86 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).

2. Calibrating sediment data to obtain a glaciological time series
Within this project we plan to produce 100 year long detailed time series of dynamic ice mass loss for selected glaciers on the basis of sediment cores. This will be done by relating the marine sediment cores, which contain detailed proxy records of the relative variability of outlet glacier iceberg production during the past c. 100 years, with concurrent low-resolution, but specific dynamic ice mass changes. The time period chosen for conversion is the period from the end of the Little Ice Age (c. 1900) into present, since only this period is covered by both estimates of specific ice dynamic ice mass change and sediment records.
The low resolution record of specific ice mass changes are produced by using digital elevation models (DEMs), which are constructed for the selected glaciers on the basis of historical aerial photographs. This has allowed for 3D mapping of geomorphic features recognized on the aerial imagery such as trim lines on valley sides produced by an extended Inland Ice sheet during the marked Little Ice Age cooling.

3. Tuning of a glacier model and prediction of future mass loss
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 (100 years). 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. 

Sediment and its microfossils tell tales of past changes in glaciers and ocean conditions.

Short movie Fieldwork SE Greenland


Relevant references

Andresen, C. S., Straneo, F., Ribergaard, M. H., Bjørk, A. A., Andersen, T.J., Kuijpers, A., Nørgaard-Pedersen, N., Kjær, K. H., Schjøth, F., Weckström, K. and Ahlstrøm, A. P. 2012: Rapid response of Helheim Glacier in Greenland to climate variability over the past century. Nature Geoscience 5, 37-41, doi:10.1038/ngeo1349.

Andresen, C., McCarthy, D., Dylmer, C., Seidenkrantz, M.-S., Kuijpers, A., Lloyd, J. 2011: Interaction between subsurface ocean waters and calving of the Jakobshavn Isbræ during the late Holocene. The Holocene 21(2), 211–224.

Andresen, C. S., Schmidt, S., Seidenkrantz, M.-S., Straneo, F., Grycel, Hass, C. A., Kjær, K. H., Nørgaard-Pedersen, N., Dyke, L. M., Olsen, J. M. and Kuijpers. 2014a. A 100-year record of changes in water renewal rate in Sermilik Fjord and its influence on calving of Helheim Glacier, Southeast Greenland. Continental Shelf Research,DOI: 10.1016/j.csr.2014.05.017.

Andresen, C. S., Sicre, M.-A., Straneo, F., Sutherland, D., Schmith, T., Ribergaard, M. H., Kuijpers, A. and Lloyd, J. M. 2013b. A 100 yr record of alkenone based SST changes offshore Southeast Greenland. Continental Shelf Research. DOI: 10.1016/j.csr.2013.10.003

Andresen, C. S., Hansen, M. J., Seidenkrantz, M.-S., Jennings, Faurschou, M, Nørgaard-Pedersen, N., A. E., Larsen, N., Kuijpers, A., and Pearce, C. 2013. Mid- to Late-Holocene oceanographic variability on the Southeast Greenland shelf. The Holocene DOI: 10.1177/0959683612460789.

Andresen, C.S., Nørgaard-Pedersen, N., Jensen, J. B., and Larsen, B. 2010: Southeast Greenland ice-sheet variability elucidated by shallow seismic survey and sediment coring in the Sermilik Fjord near the Helheim Glacier in 2009. Geological Survey of Denmark and Greenland Bulletin 20, 83-86.

Andresen, C. S., Kjeldsen, K. K., Harden, B., Nørgaard-Pedersen, N. and Kjær, K. H. 2014b. Outlet glacier dynamics and bathymetry at Upernavik Isstrøm and Upernavik Isfjord, North-West Greenland. Geological Survey of Denmark and Greenland Bulletin 31, 79-82.

Dyke, L. M., Hughes, A. L. C., Murray, T., Hiemstra, J. F., Andresen, C. S. and Rodés 2014. A. Asynchronous deglaciation of large outlet glaciers in southeast Greenland. Quaternary Science Review DOI: 10.1016/j.quascirev.2014.06.001

Bjørk, A. A., Kjær, K. H., Korsgaard, N. J., Khan, A., S., Kjeldsen, K. K., Andresen, C. S., Box, J. E., Larsen, N. K. and Funder, S. 2012. Historical aerial photographs uncover eighty years of ice-climate interaction in southeast Greenland. Nature Geoscience 5, Pages: 427–432 Year published:DOI: doi:10.1038/ngeo1481

Schjøth, F., Andresen, C. S., Straneo, F., Murray, T., Scharrer, K. and Korablev, A. 2012: Campaign to map the bathymetry of a major Greenland fjord. Eos Transactions, American Geophysical Union (Brief Report) 93 (14), p.1

Håkansson, L., Briner, J. P., Andresen, C. S., Thomas, E. K., Bennike, O. 2014. Slow retreat of a land-based sector of the West Greenland Ice Sheet during the Holocene Thermal Maximum: evidence from threshold lakes at Paakitsoq. Quaternary Science Reviews 98, 74-83 DOI:10.1016/j.quascirev.2014.05.016 


Past and future dynamics of the Greenland Ice Sheet