Sedimentary organic carbon and nitrogen contents and their isotopic compositions along two transects on the East China Sea shelf.

Abstract

Surficial sediment samples were collected from two transects on the shelf of the East China Sea: one across the shelf and the other along the coast, both starting near the Changjiang river mouth. They were analyzed for contents of total nitrogen (TN%) and total organic carbon (TOC%) and for their isotopic compositions (δ15N and δ13CTOC). The TOC% and TN% values varied concomitantly in the ranges of 0.2 to 1.5% and 0.02 to 0.19%, respectively. The δ13CTOC value ranged from −25.1 to −19.6‰. The lower δ13CTOC values ( 0.5%). Away from the coastal zone, TOC% dropped sharply with corresponding increase in the δ13CTOC value. The δ15N value, varying from 3.6 to 4.9‰, displayed a more complicated distribution pattern. Distinctively lower δ15N values (<4.1‰) occurred near the Changjiang river mouth and near the shelf edge. Isotopically light riverine nitrogenous materials and preferential uptake of isotopically light nitrogen in the rich supply of nutrients in the Changjiang plume may have contributed to the observed low values near the river mouth, while nitrogen fixers in the Kuroshio waters may have contributed to those near the shelf break.