Potentially Bioavailable Iron Delivery by Iceberg-hosted Sediments and Atmospheric Dust to the Polar Oceans

Abstract

Iceberg-hosted sediments and atmospheric dusts transport potentially bioavailable iron to the Arctic and Southern Oceans as nanoparticulate ferrihydrite (the most soluble and potentially bioavailable iron (oxyhydr)oxide mineral). A suite of more than 50 iceberg-hosted sediments contain a mean content of 0.076 wt. % Fe as nanoparticulate ferrihydrite, which produces iceberg-hosted Fe fluxes ranging from 1.4–11 and 3.2–25 Gmoles yr^−1 to the Arctic a nd Southern Oceans respectively. Atmospheric dust contains a mean nanoparticulate ferrihydrite Fe content of 0.038 wt. % (corresponding to a fractional solubility of ~ 1 %) and delivers much smaller Fe fluxes (0.02–0.07 Gmoles yr^−1 to the Arctic Ocean and 0.0–0.02 Gmoles yr^−1 to the Southern Ocean). New dust flux data show that most atmospheric dust is delivered to sea ice where exposure to melting/re-freezing cycles may enhance fractional solubility, and thus fluxes, by a factor of approximately 2.5. Improved estimates for these particulate sources require additional data for the sediment content of icebergs and samples of atmospheric dust delivered to the polar regions.