Sensitivity of ocean biogeochemistry to the iron supply from the Antarctic ice sheet explored with a biogeochemical model

Abstract. Iron (Fe) delivery by the Antarctic Ice Sheet(AIS) through ice shelfand icebergmelting enhances primary productivityin the largely iron-limited Southern Ocean (SO). To explore this fertilization capacity, we implemented a simple representation of the AIS iron source in the global ocean biogeochemical model NEMO-PISCES. We evaluated the response of Fe, surface chlorophyll, primary productionand carbon export to the magnitude and hypothesized vertical distributions of the AIS Fe fluxes. Surface Fe and chlorophyll concentrations are increased up to 25 % and 12 %, respectively, over the whole SO. The AIS Fe delivery is found to have a relatively modest impact on SO primary productionand C export which are increased by 0.063 ± 0.036 PgC yr −1 and 0.028 ± 0.016 PgC yr −1 , respectively. However, in highly fertilized areas, primary productionand C export can be increased by up to 30 % and 42 %, respectively. Icebergsare predicted to have a much larger impact on Fe, surface chlorophyll and primary productivitythan ice shelves in the SO. The response of surface Fe and chlorophyll is maximum in the Atlantic sector, northeast of the tip of the Antarctic Peninsula, and along the East Antarctic coast. The icebergFe delivery below the mixed layer may, depending on its assumed vertical distribution, fuel a non-negligible subsurface reservoir of Fe. The Fe supply is effective all year round and seasonal variations in icebergmelting have regional impacts which are almost negligible for annual- mean primary productivityand C export at the scale of the SO.