Evaluating the importance of atmospheric and sedimentary iron sources to Southern Ocean biogeochemistry

The predominant iron sources to the Southern Ocean (SO) are atmospheric deposition and sediment supply from the continental margin and their relative importance in governing SO carbon export remains a subject of great debate. Here we report the results of simulations conducted with an ocean general circulation and biogeochemistry model (OGCBM) to quantify the importance of each source at different spatial scales at quasi-equilibrium. Overall, we find sediment derived iron is more important than dust derived iron in sustaining SO export production (by 1.4 to 9 times). Although dust iron is important in certain geographic sectors of the SO, this largely depends on the dust model employed. Apparent geographical correlations between dust deposition and export production can be misleading, since sediment iron can be transported to similar regions. Future generation OGCBMs must better represent spatial variability in deposition fluxes and iron solubility from dust, as well as the poorly constrained, yet regionally important, sediment Source.