Preprints
https://doi.org/10.5194/bg-2021-79
https://doi.org/10.5194/bg-2021-79

  08 Apr 2021

08 Apr 2021

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

Seasonal dispersal of fjord meltwaters as an important source of iron to coastal Antarctic phytoplankton

Kiefer Forsch1, Lisa Hahn-Woernle2, Robert Sherrell3, Joe Roccanova3, Kaixan Bu3, David Burdige4, Maria Vernet1, and Katherine A. Barbeau1 Kiefer Forsch et al.
  • 1Scripps Institution of Oceanography, University of California San Diego, La Jolla, 92037, USA
  • 2Department of Oceanography, University of Hawai`i, Manoa, 96822, USA
  • 3Department of Marine and Coastal Sciences, Rutgers University, New Brunswick, 08901, USA
  • 4Department of Ocean & Earth Sciences, Old Dominion University, Norfolk, 23529, USA

Abstract. Glacial meltwater from the western Antarctic Ice Sheet is hypothesized to be an important source of cryospheric iron, fertilizing the Southern Ocean, yet its trace metal composition and factors which control its dispersal remain poorly constrained. Here we characterize meltwater iron sources in a heavily glaciated western Antarctic Peninsula (WAP) fjord. Using dissolved and particulate ratios of manganese-to-iron in meltwaters, porewaters, and seawater, we show that glacial melt and subglacial plumes contribute to the seasonal cycle of bioavailable iron within a fjord still relatively unaffected by climate change-induced glacial retreat. Organic ligands derived from the phytoplankton bloom and the glaciers bind dissolved iron and facilitate the solubilization of particulate iron downstream. Using a numerical model, we show that plumes generated by outflow from the subglacial hydrologic system, enriched in labile particulate trace metals derived from a chemically-modified crustal source, can supply the surface through vertical mixing, and that prolonged katabatic wind events enhance export of meltwater out of the fjord. Thus, we identify an important atmosphere-ice-ocean coupling intimately tied to coastal iron biogeochemistry and primary productivity along the WAP.

Kiefer Forsch et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Review - Seasonal dispersal of fjord meltwaters as an important source of iron to coastal Antarctic phytoplankton', Anonymous Referee #1, 20 Apr 2021
    • AC1: 'Reply on RC1 on behalf of all co-authors', Kiefer Forsch, 12 Jun 2021
  • RC2: 'Comment on bg-2021-79', Anonymous Referee #2, 30 Apr 2021
    • AC2: 'Reply on RC2', Kiefer Forsch, 12 Jun 2021

Kiefer Forsch et al.

Kiefer Forsch et al.

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Short summary
In this study, we found that the seasonality of iron in a western Antarctic Peninsula (WAP) fjord is linked to the dispersal of iron-rich meltwater sources. Using geochemical measurements of trace metals in meltwaters, porewaters, and seawater, collected during two expeditions, contributions to the seasonal cycle were constrained. Model results revealed that the dispersal of surface meltwater and iron-rich meltwater plumes originating from under the glacier is sensitive to katabatic wind events.
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