| Summary: | The Antarctic continental shelf supports a high level of marine primary productivity and is a globally importantcarbon dioxide (CO 2 ) sink through the photosynthetic fixation of CO 2 via the biological pump. Sustaining suchhigh productivity requires a large supply of the essential micronutrient iron (Fe); however, the pathways for Fedelivery to these zones vary spatially and temporally. Our study is the first to report a previously unquantifiedsource of concentrated bio-available Fe to East Antarctic surface waters. We hypothesize that Fe derived fromsubglacial processes is delivered to euphotic waters through the accretion (Fe storage) and subsequent melting (Ferelease) of a marine-accreted layer of ice at the base of the Amery Ice Shelf. Using satellite-derived Chlorophyll-adata, we show that the soluble Fe supplied by the melting of the marine ice layer is an order of magnitude largerthan the required Fe necessary to sustain the large annual phytoplankton bloom in Prydz Bay. Our finding of highconcentrations of Fe in AIS marine ice and recent data on increasing rates of ice shelf basal melt in many ofAntarcticas ice shelves [Paolo et al., 2015] should encourage further research into glacial and marine sedimenttransport beneath ice shelves and their sensitivity to current changes in basal melt. This research also encouragenew research into the formation of marine ice and its vulnerability to a warming ocean. Currently, the distribution,volume and Fe concentration of Antarctic marine ice is poorly constrained. This uncertainty, combined withvariable forecasts of increased rates of ice shelf basal melt, limits our ability to predict future Fe supply toAntarctic coastal waters.
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