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Front. Mar. Sci. | doi: 10.3389/fmars.2019.00412

Influence of glacial meltwater on summer biogeochemical cycles in Scoresby Sund, East Greenland

  • 1Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), Germany
  • 2Institute of Biology and Environmental Sciences, Faculty V Mathematics and Natural Sciences, Carl von Ossietzky University Oldenburg, Germany
  • 3Helmholtz-Institut für Funktionelle Marine Biodiversität (HIFMB), Germany
  • 4Hochschule Bremerhaven, Germany
  • 5Center for Marine Environmental Sciences, University of Bremen, Germany

Greenland fjords receive considerable amounts of glacial meltwater discharge from the Greenland Ice Sheet due to present climate warming. This impacts the hydrography via freshening of the fjord waters and biological processes due to altered nutrient input and the addition of silts. We present the first comprehensive analysis of the summer carbon cycle in the world's largest fjord system situated in southeastern Greenland. During a cruise onboard RV Maria S. Merian in summer 2016, we visited Scoresby Sund and its northernmost branch, Nordvestfjord. In addition to direct measurements of hydrography, biogeochemical parameters and sediment trap fluxes, we derived net community production (NCP) and full water column particulate organic carbon (POC) fluxes, and estimated carbon remineralization from vertical flux attenuation. While the narrow Nordvestfjord is influenced by subglacial and surface meltwater discharge, these meltwater effects on the outer fjord part of Scoresby Sund are weakened due to its enormous width. We found that subglacial and surface meltwater discharge to Nordvestfjord significantly limited NCP to 32 – 36 mmol C m-2 d-1 compared to the outer fjord part of Scoresby Sund (58 – 82 mmol C m-2 d-1) by inhibiting the resupply of nutrients to the surface and by shadowing of silts contained in the meltwater. The POC flux close to the glacier fronts was elevated due to silt-ballasting of settling particles that increases the sinking velocity and thereby reduces the time for remineralization processes within the water column. By contrast, the outer fjord part of Scoresby Sund showed stronger attenuation of particles due to horizontal advection and, hence, more intense remineralization within the water column. Our results imply that glacially influenced parts of Greenland's fjords can be considered as hotspots of carbon export to depth. In a warming climate, this export is likely to be enhanced during glacial melting. Additionally, entrainment of increasingly warmer Atlantic Water might support a higher productivity fjord systems. It therefore seems that future ice-free fjord systems with high input of glacial meltwater may become increasingly important for Arctic carbon sequestration.

Keywords: Arctic fjords, Greenland, Carbon Cycle, Net community production, Meltwater discharge, glaciers, Scoresby Sund, biogeochemical cycling

Received: 30 Oct 2018; Accepted: 04 Jul 2019.

Edited by:

Maria Vernet, University of California, San Diego, United States

Reviewed by:

Mattias R. Cape, School of Oceanography, University of Washington, United States
Tomas Torsvik, Norwegian Polar Institute, Norway  

Copyright: © 2019 Seifert, Hoppema, Burau, Friedrichs, Geuer, John, Koch, Konrad, van der Jagt and Iversen. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Dr. Morten H. Iversen, Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), Bremerhaven, 27570, Bremen, Germany, morten.iversen@awi.de