Hydrothermal contribution to the oceanic dissolved iron inventory

Iron limits phytoplankton growth and hence the biological carbon pump in the Southern Ocean(1). Models assessing the impacts of iron on the global carbon cycle generally rely on dust input and sediment resuspension as the predominant sources(2,3). Although it was previously thought that most iron from deep-ocean hydrothermal activity was inaccessible to phytoplankton because of the formation of particulates(4), it has been suggested that iron from hydrothermal activity(5-7) may be an important source of oceanic dissolved iron(8-13). Here we use a global ocean model to assess the impacts of an annual dissolved iron flux of approximately 9 x 10(8) mol, as estimated from regional observations of hydrothermal activity(11,12), on the dissolved iron inventory of the world's oceans. We find the response to the input of hydrothermal dissolved iron is greatest in the Southern Hemisphere oceans. In particular, observations of the distribution of dissolved iron in the Southern Ocean(3) (Chever et al., manuscript in preparation; Bowie et al., manuscript in preparation) can be replicated in our simulations only when our estimated iron flux from hydrothermal sources is included. As the hydrothermal flux of iron is relatively constant over millennial timescales(14), we propose that hydrothermal activity can buffer the oceanic dissolved iron inventory against shorter-term fluctuations in dust deposition.