Cross-shelf transport of terrestrial Al enhanced by the transition of northeasterly to southwesterly monsoon wind over the East China Sea

Abstract

Aluminum (Al) is one of the key parameters of GEOTRACES. In spring 2011, we examined the distribution of dissolved Al in the East China Sea (ECS) to assess the potential passage of coastal water across the shelf to the western Pacific. Measurement of dissolved Al in coastal, shelf, and shelf break waters indicated decreasing concentrations with distance from the coast. However, the northward increase of dissolved Al in the upper 100 m along the shelf break transect, corresponding to the northward flow of Kuroshio Water along the Okinawa Trough from the north of Taiwan to the Tokara strait, indicates contributions of terrestrial material. The presence of an Al plume indicated cross-shelf transport at the subsurface at a potential density of 23.3–24.0 kg/m3. This plume originates from the near-bottom layer along the coast off Zhejiang and Fujian Provinces, and first moves southeastward (to the north of Taiwan) and then northeastward (to shelf break with export at 29°N, 127°E). We calculated the cross-shelf fluxes of water and dissolved Al based on simulation results of the 3-D Massachusetts Institute of Technology general circulation model (MITgcm). The calculated cross-shelf fluxes of Al at the subsurface layer indicate that the ECS is highly efficient in pumping Al-rich coastal waters northward to the Japan Sea/East Sea and/or eastward into the western Pacific. We also identified an important role of the monsoon, with a change from northeasterly wind to southwesterly wind in spring, on the cross-shelf transport of Al by use of numerical tracer experiments.