Abstract
North African dust is known to be deposited in the Gulf of Mexico, but
its deposition rate and associated supply of lithogenic dissolved
metals, such as the abiotic metal thorium or the micronutrient metal
iron, have not been well-quantified. 232Th is an isotope with similar
sources as iron and its input can be quantified using radiogenic 230Th.
By comparing dissolved 232Th fluxes at three sites in the northern Gulf
of Mexico with upwind sites in the North Atlantic, we place an upper
bound on North African dust contributions to 232Th and Fe in the Gulf of
Mexico, which is about 30% of the total input. Precision on this bound
is hindered by uncertainty in the relative rates of dust deposition in
the North Atlantic and the northern Gulf of Mexico. Based on available
radium data, shelf sources, including rivers, submarine groundwater
discharge and benthic sedimentary releases are likely as important if
not more important than dust in the budget of lithogenic metals in the
Gulf of Mexico. In other words, it is likely there is no one dominant
source of Th and Fe in the Gulf of Mexico. Finally, our estimated Fe
input in the northern Gulf of Mexico implies an Fe residence time of
less than 6 months, similar to that in the North Atlantic despite
significantly higher supply rates in the Gulf of Mexico.