Lateral Transport of Lithogenic Particles from the Continental Margin of the Southern East China Sea

Abstract

Geochemical compositions and fluxes of suspended and trapped (settling) particulate matter were studied to elucidate particle sources and transports from the continental margin of southern East China Sea (ECS) to the Okinawa Trough. Experimental results indicate that the abundance of suspended particulate matter (SPM) and lithogenic elements (Al, Fe and Mn) decreases with an increase of distance from the land, but increases with water depth, implying the resuspension and lateral transport of SPM over the southern ECS shelf and upper slope. This transport process is further demonstrated by a decrease of mass flux from the Mien-Hwa Canyon (MHC) to the Okinawa Trough, but an increase of mass flux with depth for trapped particulate matter (TPM). In addition, mass fluxes are anomalously high and substantially greater within the MHC (6·64–71·5gm−2day−1) than nearby slope areas (0·77–15·7gm−2day−1) and other globally analogous environments. MHC appears to function as an essential conduit for particle transport. Both SPM and TPM collected below the surface layer are mainly lithogenic. Approximately 76·2–89·3% of TPM are lithogenic materials regardless of trap sites, strongly indicating that laterally lithogenic sources must add to vertical mass fluxes across the margin. Biogenic contributions are relatively small, ranging from 1·05 to 6·54% for organic matter, from 6·33 to 14·3% for carbonate and from 0·67 to 3·50% for opal, resulting from dilution by lithogenic materials. Vertical fluxes may just contribute 8–34% of Corg fluxes collected from bottom traps. Statistical correlations among Al, K, Mn, Mg and Fe contents are highly significant, also reflecting that TPM is primarily lithogenic. However, only 40–73% of collected TPM may be regarded as recent inputs from the Yangtze River. Particles resuspended and advected from shelf and/or slope may contribute significantly to TPM collected between the upper slope and the Okinawa Trough. Furthermore, short-term variabilities of mass and lithogenic fluxes on all trap occupations may arise from episodic events of resuspension/lateral transport, rather than from temporal variations of riverine inputs and local production.