Modeling the tidewater glacier Kangiata Nunaata Sermia and the freshwater flux into Godthaabsfjorden

The Greenland ice sheet loses mass due to changing surface mass balance, direct melting on the surface, ice flow through the numerous outlet glaciers, and basal melt. My work focuses on the outlet glaciers terminating in Godthaabsfjord near Nuuk in West Greenland, with Kangiata Nunaata Sermia (KNS) being the main contributing glacier. The mass loss of this glacier forms a small contribution to the total mass loss of the Greenland ice sheet, but it will have a large impact on the local ecosystem when there is a large freshwater flux into the fjord. Here, two independent methods are used to estimate the total mass loss by KNS and its neighboring outlets, namely an ice sheet model applied to KNS and stable oxygen isotope measurements in the fjord.

The Parallel Ice Sheet Model (PISM) is applied to model current and future mass loss. A parameter study is conducted to select the best parameter settings matching observed surface velocities and observed ice thickness. A monthly mean climatic forcing is applied to these best settings to investigate the individual components of the total fluxes. The model reproduces the present behavior of KNS. Also, seasonal variations are modeled. The modeled solid ice flux, surface velocities, and total mass flux agree well with the observed surface velocities, calving flux estimates, and elevation changes. The glacier is currently losing mass and will continue to lose mass. Using present day climate without additional warming, the KNS drainage basin will likely suffer a mass loss of (4.2±2.9) km3/yr water equivalent (w.e.). The best model run suggests a mass loss of 3.0 km3/yr w.e. until 2050. Adding an increase in temperature, following the Representative Concentration Pathway (RCP) scenarios, the expected mass loss is (10.3±2.6) km3/yr w.e until 2050.

Due to the lack of successful bed elevation measurements, the bed topography underneath KNS is basically unknown. Here, a simple iterative method is presented to adjust the bedrock map using observed surface velocities. This method is tested on Greenland's largest outlet glacier, Jakobshavn Isbrae, and applied to KNS afterwards.

Also, available data on freshwater fluxes from land and glaciers and measurements of salinity and stable oxygen isotopes in Godthaabsfjord, taken between 2007 and 2010, are used in order to determine the relative contribution from the various freshwater sources into the fjord. To this end, the seasonal signal of salinity and stable oxygen isotopes is analyzed. A box model is used to compute the freshwater contributions from the glaciers from oceanographic measurements. The model identifies critical parameters for quantifying glacial meltwater and run-off into the fjord system. These critical parameters include the stable oxygen isotope composition of glacial ice, run-off and seawater, and transport in the surface layer. With a better knowledge of the discussed parameters, such as the velocity in the surface layer and the isotopic signature of glacial ice, the uncertainties in the estimates of the various freshwater sources can be reduced significantly. According to this study, there is (11.5±2.3) km3/yr freshwater entering the fjord, (7.8±6.4) km3/yr of which from glacial meltwater (excluding surface melt) and (3.8±8.7) km3/yr of which from run-off of surface melt water. Downscaling the modeled results allow us to estimate the individual glacier contributions. KNS contributes 4.8 km3/yr glacial meltwater and 1.4 km3/yr run-off. Hence, the total freshwater coming from this glacier is 6.2 km3/yr.



Publications

  1. Modeling Present and Future Behavior of the Tidewater Glacier Kangiata Nunaata Sermia, West Greenland
    A. Fitzner and D. Dahl-Jensen
    submitted to The Cryosphere
  2. Estimating the glacial meltwater contribution to the freshwater budget from salinity and d18O measurements in Godthaabsfjord
    A. Fitzner, D. van As, J. Bendtsen, D. Dahl-Jensen, X. Fettweis, S. Rysgaard
    submitted to Journal of Geopysical Research
  3. Glacier dynamics at Helheim and Kangerdlugssuaq glaciers, southeast Greenland, since the Little Ice Age
    S.A. Khan, K.K. Kjeldsen, K.H. Kjaer, S. Bevan, A. Luckman, A. Aschwanden, N.J. Korsgaard, A.A. Bjork, J. Box, M. van den Broeke, T. van Dam, and A. Fitzner
    The Cryospere, Vol. 8, No. 4, 2014
  4. Angular reconstruction with less than three SD stations using relative PMT signals
    A. Fitzner, S. Grebe, H. Schoorlemmer, C. Timmermans
    Pierre Auger Collaboration Internal Publication (GAP-2010-053), May 2010

Posters

EGU 2013 Poster: Estimating the glacial meltwater contribution to the fresh water budget from salinity and d18O measurements in Godthaabsfjord
EGU 2013 Poster: Modeling the present and future behavior of the glaciers terminating into Godthaabsfjord, West Greenland
Poster presented at the IGS symposium in Fairbanks
Poster presented at EGU 2012