Trace metal composition of size‐fractionated plankton in the Western Philippine Sea: The impact of anthropogenic aerosol deposition

Abstract

The surface water of the Western Philippine Sea (WPS) receives a significant amount of anthropogenic aerosols from East Asia, serving as an ideal location to investigate the impact of anthropogenic aerosol deposition on trace metal composition and cycling in the Northwestern Pacific Ocean (NWPO). As part of the Taiwan GEOTRACES process study, we have collected size-fractionated plankton from surface water to investigate their metal composition in the open ocean. Elemental ratios in plankton, P-and Al-normalized, are used to evaluate the sources of trace metals and the relative contribution of different metal components in plankton assemblages. Most of the trace metal quotas in plankton are one to two orders of magnitude higher than their intracellular plankton quota, indicating that the majority of the metals are most likely to be extracellularly adsorbed or aggregated on plankton. The metal to Al ratios for most of the trace metals in plankton are also one to two orders of magnitude higher than their lithogenic composition, but are relatively close to metal composition in aerosols collected in situ. This supports the notion that particulate trace metals associated with plankton mainly originate from anthropogenic aerosols, not lithogenic particles. Compared to plankton metal quotas obtained in other oceanic regions, trace metal quotas observed in the WPS rank among the highest for Fe, Mn, Zn, and Cu globally. Our study demonstrates that anthropogenic aerosol deposition has significantly elevated trace metal concentrations in the size-fractionated plankton in the surface water of the NWPO relative to the biological requirements.

Particulate Trace Metal Composition and Sources in the Kuroshio Adjacent to the East China Sea: The Importance of Aerosol Deposition

“…Then all the membranes were immediately sealed in 7‐ml Teflon vials and brought back to land‐based laboratory for further treatment and analysis. The sampling procedures and the description of the filtration device are described in details in our previous studies (Ho et al, ; Liao et al, ).…”

“…All elemental concentrations reported were analyzed by a sector field high‐resolution ICPMS (Thermo Fisher Scientific, Element XR), which was executed with a SC‐Fast autosampler (Elemental Scientific) and an Apex HF‐Spiro membrane desolvation device (Elemental Scientific) to reduce oxide interferences. The details for the precision, accuracy, and detection limits of the method were described previously (Ho et al, ; Liao et al, ). The overall procedure blanks, detection limits, and the recovery of the reference material (BCR‐414) obtained in this study were consistent with results reported in Liao et al ().…”

“…The details for the precision, accuracy, and detection limits of the method were described previously (Ho et al, ; Liao et al, ). The overall procedure blanks, detection limits, and the recovery of the reference material (BCR‐414) obtained in this study were consistent with results reported in Liao et al (). In addition to the validation of the reference material, our laboratory also obtained reliable results during the GEOTRACES particulate trace metal intercalibration study, which included relatively low mass particulate samples collected at both coastal and open ocean locations (Phoebe Lam, personal communication, March 29, 2016).…”

“…Particulate trace metals in the Kuroshio adjacent to the ECS may originate from various terrestrial sources, including aerosol deposition, riverine discharges, submarine groundwater discharge, and sediment transport or bottom resuspension. Our previous studies have demonstrated that anthropogenic aerosol deposition is the dominant source of particulate trace metal in the surface water of the SCS and the Western Philippine Sea (WPS; Ho et al, ; Liao et al, ). The role of aerosol deposition in the Kuroshio region can be significant due to the proximity of East Asia.…”

“…The annual average geostrophic velocity in the top 50 m was derived from a numerical study (Hsin et al, ). The data, obtained from our previous study in November 2013 (Liao et al, ), from stations A, B, and 1, were also included in this study for comparison.…”