Variations of Calcium Carbonate, Organic Carbon and Their Isotopic Compositions in Surface Sediments of the East China Sea

東海表層沈積物其碳酸鈣、有機碳及其同位素組成之分佈變化

許德惇(David D. Sheu)；周文臣(Wen-Chen Jou)；陳明助(Ming-Jue Chen)；李維元(Way-Yuan Lee)；林曉武(Saulwood Lin)

Calcium carbonate ； Organic carbon ； Carbon and oxygen isotopes ； n-alkanes ； the East China Sea

Terrestrial, Atmospheric and Oceanic Sciences

6卷1期（1995 / 03 / 01）

115 - 128

英文

This study analyzes the carbonate and organic carbon contents and their carbon and oxygen isotopic compositions of a total of 58 surface sediment samples from the continental margin of the East China Sea. Additional gas chromatographic (GC) analysis of selected sediment samples was performed to show typical concentration and distribution of n-alkanes in these sediments. Results show that carbonate contents of sediments in the region are highly variable from 3.0 to 63.1 wt% across the shelf, yet they show an increase toward the south in a lobate distribution between water depths of approximately 90 and 150m. Except for some data, values of δ^13 C of carbonates in general vary in a narrow range of 0±l‰ as compared to those of δ^18 that varies considerably over a range from 0 to -6‰. Organic carbon concentrations of sediments range from 0.1 to 1.44 wt% and become enriched toward the north. δ^13 C of organic carbon varies from -22.9 to -20.1‰ and shows a vague increase (becomes heavier) with increasing distance from the coast. Results from GC analysis reveal that the n-alkane concentrations in sediments can vary up to ten-fold and are predominant with C21 -C25 compounds. Cross plots of carbonate and organic carbon concentrations vs. water depths further reveal that sediments of high carbonate content are invariably characteristic of low organic carbon contents and vice versa. Such a contrasting feature can be attributed to the winnowing effect upon sediment accumulation during low stands of sea level. Moreover, carbonates from sediments of high carbonate contents are found to be depleted in (superscript 18)O, indicative of a relic origin of the carbonates and likely the associated sediments. The pattern of n-alkane distribution reveals that the sediment mainly consists of organic matter of reworked and/or transported origins. As a consequence, geochemical and stable isotopic characterization of surface sediments in this study supports an episode of relic sedimentation in the East China Sea between the present-day water depths of approximately 90 and 150m and is thus consistent with previous observations.