Does Sea Surface Temperature Affect Solubility of Iron in Mineral Dust? The Gulf of California as a Case Study

Abstract

AbstractEolian 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.