Atmospheric iron fluxes in the northern region of the Gulf of California: Implications for primary production and potential Fe limitation

Abstract

To study the temporal variability of atmospheric mineral dust and Fe fluxes to the northern region of the Gulf of California, dust samples were collected at San Felipe, Baja California (Site 1) and Puerto Peñasco, Sonora (Site 2), from May 2010 to December 2011. Dust fluxes were partially associated with monsoon circulation, with highest (38 ± 20mgm−2 d−1) and lowest (8.8 ± 4.9mgm−2 d−1) fluxes linked to southwesterly winds (monsoon season) and north-northwesterly winds (non-monsoon season), respectively. Our analysis suggests that the surrounding deserts are the most probable source of dust arriving into the Gulf of California. However, analyses of Al and Fe concentrations in dusts showed no trends that could identify specific particulate Fe provenance. Average particulate Fe atmospheric fluxes (FeAtm) showed no clear temporal trends and their magnitudes (3.2 ± 3.4 and 6 ± 10µmolm−2 d−1 for sites 1 and 2, respectively) could be considered medium-to-low in magnitude within a global context. An Fe limitation index (FeLI), calculated as the ratio of phytoplankton Fe requirements to atmospheric and upwelling Fe fluxes, is proposed to estimate the impact of atmospheric mineral dust on phytoplankton primary production in surface waters of the Gulf of California. On a seasonal time scale, FeLI results suggest that under winter conditions, there is no evidence of Fe limitation because upwelling Fe contribution (FeUp) is high enough to support primary production. In contrast, during summer conditions, when FeUp is very low or negligible, high FeAtm combined with high particulate Fe dissolution factors could prevent the northern Gulf of California from becoming Fe-limited. Finally, we postulate that at an interannual scale, conditions prevailing during ENSO events could increase atmospheric Fe fluxes to the Gulf of California, further contributing to prevent Fe limitation in this marginal sea.