Circumpolar Deep Water and Shelf Sediments Support Late Summer Microbial Iron Remineralization

Abstract Despite widespread iron (Fe) limitation in the Southern Ocean, intense phytoplankton blooms are observed around productive coastal regions such as Mertz Polynya (off George V Land and Adelie Land, East Antarctica; 140–155°E). Sources of Fe across Antarctica vary, with limited data available for late summer months. We investigated sources dissolved (dFe; <0.2 μm) at 19 oceanographic stations Glacier Region (64–67°S; 138–154°E), between January March 2019. Concentrations dFe ranged from below detection limit (0.03 nM) surface, to 0.34 nM above base mixed layer (35 m), reaching 0.59 depth (520 m). Using features trace element ratios (manganese titanium), we identified Circumpolar Deep Water (CDW) shelf sediment resuspension modified CDW contributors region over this period. Microbial remineralization was evident where nutrient‐rich water met highly oxygenated waters continental shelf. Reduced concentrations euphotic zones suggested rapid biological uptake prior sampling. proposals pelagic recycling by marine animals, preliminary investigations reveal no significant spatial relationship animal presence surface ocean study area. Further research is required identify seasonal changes supply areas which will strengthen our understanding cycle its influence on microbial primary productivity globally region.