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General Session 2: Marine & estuarine biogeochemistry |
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The fluxes and fates of aerosol trace metals in the northern South China Sea and the Western Philippine Sea
Tuesday 10th @ 1400-1425
Conference Hall
Tung-Yuan Ho* , Academia Sinica
Presenter Email: tyho@gate.sinica.edu.tw
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| Both the northern South China Sea (NSCS) and the Western Philippine Sea (WPS) receive tremendous amount of lithogenic and anthropogenic aerosols originating from the East Asia during the high monsoon seasons (winter and spring). The oceanic regions thus provide an ideal platform to investigate the fates of aerosol trace metals and their seasonal transformation in the Northwestern Pacific Ocean (NWPO). Trace metal concentrations were determined in the size-fractionated aerosol samples (PM 2.5 and 2.5-10) collected daily in Dongsha Atoll in 2011. Two Taiwan GEOTRACES cruises were also carried out in the WPS during July 2013 and March 2014, the low and high aerosol deposition periods, respectively. In addition to aerosols, we have also measured trace metal concentrations in seawater, size-fractionated suspended particles, and sinking particles in the water column of the two oceanic regions to investigate the fates of aerosol trace metals. On average, the aerosol metal concentrations observed during the northeastern monsoon seasons are about 5 to 10 folds of the concentrations observed in the southwestern monsoon seasons. The results of the water samples show that the influence of aerosol deposition is mainly reflected in particulate pools but not dissolved pool. Using Fe as an example, total aerosol Fe deposition fluxes were 17 and 1.2 ¦̀mol Fe m-2 d-1 for the high and low seasons but dissolved Fe concentrations were relatively low (0.3 nM) and comparable between the two seasons. However, particulate Fe concentrations in the high season were 2 to 10 times of the low season in the top 100 m. In terms of size-fractionated plankton, trace metal quotas are 1 to 2 orders of magnitude higher than their intracellular plankton quota. The metal to Al ratios are also 1 to 2 orders of magnitude higher than their lithogenic composition. This study demonstrates that Asian aerosol deposition has dramatically changed trace metal composition in the suspended particles and plankton in the oceanic regions. The biogeochemical impact of aerosol deposition deserves further investigation in the oceans. |
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