Atmospheric input and concentration of dissolved iron in the surface layer of the Gulf of California

Abstract

A survey was conducted to determine the atmospheric input of particulate iron (Fe_p) and the factors and processes controlling the concentration and distribution of dissolved iron (Fe_d) in surface water (200 m) of the central Gulf of California. Atmospheric fluxes of Fep (7.0–90.4 µmol m^–2 d^–1) were of the same order of magnitude as those reported for the Red Sea (1.5–116 µmol m^–2 d^–1) and the northeastern Pacific Ocean (24 µmol m^–2 d^–1), but higher than the fluxes registered for the northwestern Mediterranean Sea (0.25–0.49 µmol m^–2 d^–1). According to the Fed concentration in surface water, three different zones were identified in the study area: a northern zone with Fe_d surface enrichment (5.57–7.21 nM) due to atmospheric input, a central zone with dilution of the Fe_d-enriched surface water by enhanced vertical mixing (0.07–0.59 nM), and a southern zone showing low Fe_d concentrations (less than 1 nM) due to biological uptake. Two types of vertical profiles were observed: (1) the typical nutrient-like distribution (with low concentrations at the surface and subsequent increase with depth) in the southern zone, and (2) mixed distribution (surface enrichment, decrease at subsurface level, and increase with depth) in the northern zone. The northern profile was 23.5 times more enriched than the adjacent Northeastern Pacific. Results indicate that Fe_d distribution in the surface layer of the central Gulf of California is controlled by complex interactions involving atmospheric input, biological uptake, and in situ removal-remineralization of particles, coupled with physical transport and vertical mixing.