Behavior of dissolved inorganic arsenic in the Yellow Sea and East China Sea

Abstract

Abstract The Yellow Sea and East China Sea are strongly affected by input from freshwater discharge (e.g., from the Changjiang (Yangtze River) in the west and the Kuroshio incursion in the east. The R/V Dong Fang Hong 2 carried out two cruises in September of 2002 and 2003 to understand the behavior of arsenic in the Yellow Sea and East China Sea. Arsenic species (total dissolved inorganic arsenic and arsenite) were determined by selective hydride generation–atomic fluorescence spectrometry. High concentrations of total dissolved inorganic arsenic species (TDIAs; [As(V)]+[As(III)]) appeared near the Changjiang Estuary and at the bottom of the shelf-break in the East China Sea where the incursion of the Kuroshio reaches the shelf. TDIAs were moderately depleted in the surface water and enriched in the deep water. The distribution of arsenite (AsO33−, As(III)) was opposite that of arsenate (AsO43−, As(V)) in seawater, but was positively correlated with that of Chlorophyll-a. The As(III)/TDIAs ratio at the surface of coastal stations was lower than 0.3 in the summer of 2002 and as high as 0.5 in the summer of 2003. A limited effect from the Changjiang discharge in September 2003 according to the salinity profile and/or high phytoplankton conversion in the study area was hypothesized for the observed interannual variation. The stoichiometric ratio of As to P in the biological assimilation was estimated to be about 2×10−3 at the PN section (a southeast transect from the Changjiang Estuary to the Ryukyu Islands) of the East China Sea in the summer. A preliminary box model was established to estimate the water-mass balance and arsenic budgets for the East China Sea Shelf in the summer. Compared with other areas in the world, the concentration of dissolved inorganic arsenic in the Yellow Sea and East China Sea remained at natural levels.