Sedimentary iron records from the Cape Basin

The “Iron Hypothesis” suggests that dust-derived Fe delivered to the Southern Ocean during glacial intervals fueled primary productivity and led to CO2 drawdown. Clear support for a dustier glacial atmosphere comes from ice-core records of dust concentrations. Furthermore, there is unequivocal proof from open-ocean Fe fertilization experiments that primary productivity in the modern-day Southern Ocean is limited by Fe. However, substantial hemipelagic detrital sources dilute and obscure the eolian signal. Here we present records of Fe concentrations (total and reducible) and Fe fluxes to highlight the importance of hemipelagic Fe sources to the Cape Basin. We illustrate that on average only 7% of the Fe flux to Site 1089 can be accounted for by particle settling, indicating that redistribution by bottom currents accounts for an order of magnitude more Fe than particulate scavenging processes, distribution by surface currents, or eolian deposition. We also find that on average only 7% of the Fe content is easily reducible. Furthermore, we speculate that a significant source of dissolved Fe to the bottom waters may come from re-suspended bottom sediments.