12 Jan 2022

12 Jan 2022

Review status: this preprint is currently under review for the journal TC.

Impact of freshwater runoff from the southwest Greenland Ice Sheet on fjord productivity since the late 19th century

Mimmi Oksman1, Anna Bang Kvorning1, Signe Hillerup Larsen1, Kristian Kjellerup Kjeldsen1, Kenneth David Mankoff1, William Colgan1, Thorbjørn Joest Andersen2, Niels Nørgaard-Pedersen3, Marit-Solveig Seidenkrantz4, Naja Mikkelsen1, and Sofia Ribeiro1 Mimmi Oksman et al.
  • 1Department of Glaciology and Climate, Geological Survey of Denmark and Greenland, Øster Voldgade 10, 1350 Copenhagen, Denmark
  • 2Department of Geosciences and Natural Resource Management, University of Copenhagen, Øster Voldgade 10, 1350 Copenhagen, Denmark
  • 3Department of Marine Geology, Geological Survey of Denmark and Greenland, C.F. Møllers Allé 8, 8000 Aarhus C, Denmark
  • 4Paleoceanography and Paleoclimate Group, Arctic Research Centre, and iClimate centre, Department of Geoscience, Aarhus University, Høegh-Guldbergs Gade 2, 8000 Aarhus C, Denmark

Abstract. Climate warming and the resulting acceleration of freshwater discharge from the Greenland Ice Sheet are impacting Arctic marine coastal ecosystems, with implications for their biological productivity. To accurately project the future of coastal ecosystems, and place recent trends into perspective, paleo-records are essential. Here, we present late 19th century to present runoff estimates for a large sub-Arctic fjord system (Nuup Kangerlua, southwest Greenland) influenced by both marine- and land-terminating glaciers. We followed a multiproxy approach to reconstruct spatial and temporal trends in primary production from four sediment cores, including diatom fluxes and assemblage composition changes, biogeochemical and sedimentological proxies (total organic carbon, nitrogen, C / N-ratio, biogenic silica, δ13C, δ15N, grain size distribution). We show that an abrupt increase in freshwater runoff in the mid-1990’s is reflected by a 3-fold increase in biogenic silica fluxes in the glacier-proximal area of the fjord. In addition to increased productivity, freshwater runoff modulates the diatom assemblages and drives the dynamics and magnitude of the diatom spring bloom. Our records indicate that marine productivity is higher today than it has been at any point since the late 19th century and suggest that increased mass loss of the Greenland Ice Sheet is likely to continue promoting high productivity levels at sites proximal to marine-terminating glaciers. We highlight the importance of paleo-records in offering a unique temporal perspective on ice-ocean-ecosystem responses to climate forcing beyond existing remote sensing or monitoring time-series.

Mimmi Oksman et al.

Status: open (until 09 Mar 2022)

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Mimmi Oksman et al.

Mimmi Oksman et al.


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Short summary
Better understanding of the cryosphere impacts on Arctic marine ecosystems is essential for accurate future projections. We present spatial and temporal trends in freshwater runoff and primary production records since the late 19th century, for a Greenlandic fjord system receiving solid and liquid discharge from the Greenland Ice Sheet. We show that climate warming, freshwater discharge and fjord productivity increased abruptly and concomitantly in the 1990’s, before monitoring efforts begun.