Particulate Trace Metal Composition in the Western Philippine Sea: the importance of anthropogenic aerosol deposition

The Western Philippine Sea (WPS), receiving huge amount of East Asian aerosols in winter and spring, is an ideal platform to investigate the impact of aerosol deposition on trace metal cycling in the oceanic surface water. Particulate trace metal composition provides useful information to elucidate the relative contribution of trace metal sources. In this study, we collected size-fractionated particles in the water column through two different seasons to investigate their trace metal composition and seasonal variability. Our results show that most of trace metal to phosphorus (P) normalized quotas in the size-fractionated particles are one to two orders of magnitude higher than intracellular trace metal quota in phytoplankton. Since all the particles collected are composed of biotic particles, the elevated trace metal to P quotas indicate that extracellular adsorption of trace metal accounts for larger amount than intracellular assimilation. In addition, the metal to Al ratios were similar to the ratios observed in aerosols, indicating that the metals mainly originated from aerosols. Overall, the extracellular adsorption of aerosol metals account for most of the particulate trace metals in the plankton samples. Our results prove the importance of aerosol metals on particulate trace metal composition in the open ocean. The impact of the input of anthropogenic aerosols on marine biogeochemistry deserves further studies in the global open ocean.