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

• Main Authors: Forsch, Kiefer, Hahn-Woernle, Lisa, Sherrell, Robert, Roccanova, Joe, Bu, Kaixan, Burdige, David, Vernet, Maria, Barbeau, Katherine A.
• Format: Text
• Language: English
• Published: 2021
• Subjects: Antarctic; Antarctic Peninsula; Southern Ocean; Antarc*; Ice Sheet
• Online Access: https://doi.org/10.5194/bg-2021-79; https://bg.copernicus.org/preprints/bg-2021-79/

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.