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

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 that 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 surface glacial melt and subglacial plumes contribute to the seasonal cycle of iron and manganese 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 buoyant plumes generated by outflow from the subglacial hydrologic system, enriched in labile particulate trace metals derived from a chemically modified crustal source, can supply iron to the fjord euphotic zone through vertical mixing. We also show 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.

Automated summary

By studying the iron sources in a heavily glaciated western Antarctic Peninsula fjord, it is revealed that surface glacial melt and subglacial plumes contribute to the seasonal cycle of iron and manganese within the environment. The study also shows that organic ligands derived from phytoplankton and glaciers play a role in the dispersion of dissolved and particulate iron downstream, while buoyant plumes enriched in labile particulate trace metals supply iron to the fjord euphotic zone. Additionally, prolonged katabatic wind events enhance the export of meltwater out of the fjord, indicating an important atmosphere-ice-ocean coupling in coastal iron biogeochemistry and primary productivity along the WAP.