The magnitude and temporal variability of mineral dust deposition and its associated Fe and Mn inputs to coastal waters of the California Current System (CCS) has been scarcely investigated. Here we report a 5 year time series (April 2010 to December 2014) of mineral dust (Fdust), Fe (FFe), and Mn (FMn) fluxes to the coastal zone of the southern CCS. Atmospheric deposition displayed a strong seasonal trend, with lowest Fdust, FFe, and FMn during the warm season (May–October), a period dominated by strong moisture‐laden winds of oceanic origin. In contrast, the highest Fdust, FFe, and FMn were recorded during the cool season (November–April), a period characterized by strong winds devoid of moisture coming from the mainland. Our analysis suggests that Santa Ana Wind events could contribute with ∼15%, 20%, and 24%, respectively, to the total annual input of dust, Fe and Mn to the region. Besides, atmospheric soluble Fe inputs are equivalent to between 11% (warm season) and 35% (cool season) of the dissolved Fe supplied by upwelling. Our calculations indicate that atmospheric Fe deposition could explain between ∼5% (warm season) and 15% (cool season) of primary production reported for the southern CCS, suggesting that this route could also be an important input of Fe for primary producers in this region. Finally, the average Fdust, FFe, and FMn for the cool seasons showed a positive interannual trend that was significantly correlated with an intensification of drought conditions over the period 2010–2014 in northwest of Mexico and southwest of the United States.

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Eolian transport of mineral dust is one of the main inputs of iron (Fe) to the global ocean; however, the magnitude and biogeochemical impact of this supply depends on the solubility of the deposited dust. In particular, the effect of temperature on Fe‐bearing dust solubility has been scarcely investigated even though a seasonal gradient of sea surface temperature (SST) is a common feature in coastal zones adjacent to the major dust source regions of the world. In this work, the effect of temperature on the fractional solubility of Fe (FFeS) was evaluated experimentally using sieved soils (as a dust proxy) from the Baja California Peninsula and surface seawater from the Gulf of California (GC). Two incubations were performed at 17°C (winter) and 29°C (summer) considering the seasonal variability of SST in the GC. Differences in FFeS up to 3 orders of magnitude (0.003–4.49%) were linked to incubation temperature, dust load, and contact time between seawater and dust. After 72 hr of incubation, the effect of temperature was statistically significant (p < 0.05) for all dust treatments, with FFeS higher (4–24 times) at 29°C. High FFeS in warmer waters are a result of increased Fe‐bearing dust dissolution and decreased scavenging of Fe by dust particles. Since temperature appears to control the magnitude of FFeS in the GC, we suggest that this factor could have an effect on the atmospheric inputs of soluble Fe in marginal seas with similar seasonal SST contrasts; including the global ocean, where well‐defined latitudinal temperature gradients exist.

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Located in the southern section of the California Current System (CCS), the coastal zone off the Baja California peninsula is an upwelling system that sustains a rich, diverse, and highly productive ecosystem. Such highprimary production is largely due to wind-driven coastal upwelling taking place mostly during the spring and early summer seasons (Linacre et al., 2010a). Besides, this region is considered an oceanographic transition zone, where the cold and low-salinity water of the California Current meets seasonally with warmer and saltier waters of tropical/subtropical origin (Durazo, 2015; Durazo et al., 2010; Kurczyn et al., 2019). Given that most of the biological and hydrographic variability in this region occurs at the seasonal and inter-annual time scales, it is valuable to understand how the system functioning is impacted by any other phenomena that increase or decrease variability at these time scales.

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The Gulf of Mexico (GoM) is one of the most dynamic marginal seas in the world owing to the intrusion of the Loop Current and the shedding of anticyclonic eddies (LCE) that travel westward across the Gulf. However, the impacts of these mesoscale dynamics on the supply and removal of bioessential trace metals in surface waters remain unclear. We study the impact of mesoscale eddies on the distribution of dissolved nickel (Ni), a biologically active element scarcely studied in the region. The vertical distribution of Ni was determined in the deep-water region of the GoM during summer of 2017, when two anticyclonic LCE (Quantum and Poseidon) were present. Nutrient-like profiles of Ni in the GoM resemble those from the Atlantic Ocean, but they showed high spatial variability within the first 1000 m, which was associated with the impact of mesoscale eddies. Similarly to subtropical gyres, macronutrients were almost depleted in surface waters, while Ni never fell below 1.51 nmol kg-1, suggesting low Ni lability or alternatively, slow biological uptake compared to that of macronutrients. In particular, lowest levels of Ni and macronutrients (PO4 and NO3) were recorded in surface waters of the anticyclonic eddies and the Loop Current area. Anticyclonic LCEs deepened these Ni-poor waters pushing the Ni-rich core of Tropical Atlantic Central Water up to 600 m, whereas its shallowest position (up to 200 m) was recorded under cyclonic conditions in Campeche Bay. This eddy-induced vertical displacement of water masses also affected the integrated Ni and macronutrient concentrations in the upper 350 m but without modifying their stoichiometries. We suggest that a significant decrease in surface inventories of Ni and macronutrient in areas impacted by LCEs is a consequence of the trapping of the water within eddies, the biological uptake of Ni and macronutrients combined with their limited replenishment from below, which likely affects autotrophic groups. In conclusion, the mesoscale dynamic permanently present in the GoM play an important role in modifying the vertical distribution of Ni and macronutrients as well as their availability in the upper water column of this marginal sea.

No abstract