Preprints
https://doi.org/10.5194/bg-2021-181
https://doi.org/10.5194/bg-2021-181

  20 Jul 2021

20 Jul 2021

Review status: a revised version of this preprint was accepted for the journal BG and is expected to appear here in due course.

Regional-scale phytoplankton dynamics and their association with glacier meltwater runoff in Svalbard

Thorben Dunse1,2, Kaixing Dong3, Kjetil Schanke Aas2, and Leif Christian Stige3,4 Thorben Dunse et al.
  • 1Department of Environmental Sciences, Western Norway University of Applied Science, Røyrgata 6, 6856 Sogndal, Norway
  • 2Department of Geosciences, University of Oslo, PO Box 1047 Blindern, NO-0316 Oslo, Norway
  • 3Centre of Ecological and Evolutionary Synthesis (CEES), Department of Biosciences, University of Oslo, PO Box 1066 Blindern, NO-0316, Oslo, Norway
  • 4Norwegian Veterinary Institute, PO Box 64, NO-1431 Ås, Norway

Abstract. Arctic amplification of global warming has accelerated mass loss of Arctic land ice over the past decades and lead to increased freshwater discharge into glacier fjords and adjacent seas. Glacier freshwater discharge is typically associated with high sediment loads which limits the euphotic depth, but may also provide surface waters with essential nutrients, thus having counter-acting effects on marine productivity. In-situ observations from a few measured fjords across the Arctic indicate that glacier fjords dominated by marine-terminating glaciers are typically more productive than those with only land-terminating glaciers. Here we combine chlorophyll a from satellite ocean colour, an indicator of phytoplankton biomass, with glacier meltwater runoff from climatic mass-balance modelling to establish a statistical model of summertime-phytoplankton dynamics in Svalbard (mid-June to September). Statistical analysis reveals positive spatiotemporal association of chlorophyll a with glacier runoff for 7 out of 14 primary hydrological regions. These regions consist predominantly of the major fjord systems of Svalbard. The adjacent land areas are characterized by a wide range of total glacier coverage (35.5 % to 81.2 %) and fraction of marine-terminating glacier area (40.2 % to 87.4 %). We find that an increase in specific glacier-runoff rate of 10 mm water equivalent per 8-day timeperiod raises summertime chlorophyll a concentrations by 5.2 % to 20.0 %, depending on region. During the annual peak discharge we estimate that glacier runoff contributes to 13.1 % to 50.2 % increase in chlorophyll a compared to situations with no runoff. This suggest that glacier runoff is an important factor sustaining summertime phytoplankton production in Svalbard fjords, in line with findings from several fjords in Greenland. In contrast, for regions bordering open coasts, and beyond 10 km distance from the shore, we do not find significant association of chlorophyll a with runoff. In these regions, physical ocean and sea ice variables control chlorophyll a, pointing at the importance of a late sea ice breakup in northern Svalbard, as well as the advection of Atlantic water masses along the West Spitsbergen Current for summertime phytoplankton dynamics. Our method allows for investigation and monitoring of glacier-runoff effects on primary production throughout the summer season and is applicable on a Pan-Arctic scale, thus complementing valuable but scarce in-situ measurements in both space and time.

Thorben Dunse et al.

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-181', Anonymous Referee #1, 03 Aug 2021
    • AC1: 'Reply on RC1', Thorben Dunse, 17 Sep 2021
    • AC2: 'Reply on RC1', Thorben Dunse, 17 Sep 2021
  • RC2: 'Comment on bg-2021-181', Anonymous Referee #2, 27 Aug 2021
    • AC3: 'Reply on RC2', Thorben Dunse, 17 Sep 2021
  • RC3: 'Comment on bg-2021-181', Anonymous Referee #3, 27 Aug 2021
    • AC4: 'Reply on RC3', Thorben Dunse, 17 Sep 2021

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2021-181', Anonymous Referee #1, 03 Aug 2021
    • AC1: 'Reply on RC1', Thorben Dunse, 17 Sep 2021
    • AC2: 'Reply on RC1', Thorben Dunse, 17 Sep 2021
  • RC2: 'Comment on bg-2021-181', Anonymous Referee #2, 27 Aug 2021
    • AC3: 'Reply on RC2', Thorben Dunse, 17 Sep 2021
  • RC3: 'Comment on bg-2021-181', Anonymous Referee #3, 27 Aug 2021
    • AC4: 'Reply on RC3', Thorben Dunse, 17 Sep 2021

Thorben Dunse et al.

Thorben Dunse et al.

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Short summary
We investigate the effect of glacier meltwater on phytoplankton dynamics in Svalbard. Phytoplankton forms the basis of the marine food web, and its seasonal dynamics depend on the availability of light and nutrients, both of which are affected by glacier runoff. We use satellite ocean colour, an indicator of phytoplankton biomass, and glacier mass balance modelling, to find that the overall effect of glacier runoff on marine productivity is positive within the major fjord systems of Svalbard.
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