Dust deposition to the surface waters of the western and central North Pacific inferred from surface water dissolved aluminum concentrations

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Abstract

[1] Dissolved Al was determined on ∼3500 surface water samples collected in the NW Pacific during the 2002 Intergovernmental Oceanographic Commission (IOC) Contaminant Baseline survey. In addition, dissolved Al was determined on samples collected at 9 vertical stations occupied along the cruise track. Surface water Al distributions, when converted to annual mineral dust deposition (Measures and Brown, 1996), imply extremely low depositions (mean values ≤0.3 g m−2 yr−1) to surface waters of the subarctic gyre despite the atmospheric transport of large amounts of mineral dust across this region from the desert regions of China. The calculated deposition values are also much lower than the 1–10 g m−2 yr−1 predicted for this region by the GESAMP model (Duce et al., 1991). The lowest mineral dust depositions correspond to the High Nutrient Low Chlorophyll (HNLC) region of the NW Pacific, which implies that the biogeochemical status of this region is the result of low atmospheric micronutrient input, similar to other HNLC regions. In the subtropical gyre the Al-derived dust deposition (mean values 0.1–0.6 g m−2 yr−1) agrees well with the (<1 g m−2 yr−1) predictions of the GESAMP model. Enriched concentrations of dissolved Al in the coastal waters near Kauai, from fluvial sources, indicate the potential role of remote high islands in adding reactive trace elements to the nearby surface waters. In the vertical profiles, elevated dissolved Al concentrations (4–8 nM) were found to correspond to the potential density of the western Pacific “Subtropical Mode” waters which form in the recirculation zone of the Kuroshio.

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