Dissolved iron distributions in the central region of the Gulf of California,México

We report dissolved iron (Fe_d) concentrations measured in the upper 600 m in the central region of the Gulf of California (GC) under spring conditions. Our results showed the complex nature of Fe cycling within the GC. In the northern region of the study area, surface waters were relatively enriched, with Fe_d concentrations >5.0 nM, which can be partially explained by an atmospheric source. These concentrations are 12 times higher than those found in the adjacent Pacific Ocean. In contrast, Fe_d depth profiles in the southern region did not show any Fe_d surface enrichment (concentrations <1.5 nM) because of particle scavenging and higher stratification of the water-column. The most southern station in our area of study was the most stratified and showed an excess Fe_d and PO₄ with respect to NO₃, conditions favorable for nitrogen fixation. This station also showed the least negative surface value of N* of all stations. However, despite the adequate levels of Fe_d and PO₄ at that location, the surface temperature (22.6 °C) was probably not high enough for diazotrophs to develop. A slight increase in Fe_d levels in intermediate waters at the southern region was associated with the oxygen minimum zone. Finally, our results suggest that remineralization of organic matter is probably the major source of Fe_d in subsurface waters of the GC.