Lipids in suspended matter and sediments from the East China Sea Shelf

Abstract

Total suspended matter (TSM) and sediment samples from the East China Sea (ECS) Shelf were analyzed for aliphatic hydrocarbons, alkanols and sterols. TSM samples showed a strong predominance of n-C 17, pristane, n-C 18, n-C 19, n-C 19:1, n-C 21:6 and squalene, being attributed to plankton inputs. Stations with high percentages of these hydrocarbons were generally situated near the Changjiang River mouth. Three stations with highest concentrations of n-C 21:6 were located in the hot spot of chlorophyll reported in the literature (Gong et al., 1996, Continental Shelf Research 16, 1561–1590). Phytol (the most abundant alcohol in TSM) and C 20:1 and C 22:1 n-alkenols were dominant in the alcohol fraction, being representative of plankton contributions. The sterol composition of TSM was dominated by 24-methylcholesta-5,22E-dien-3β-ol, cholest-5-en-3β-ol, cholesta-5,22E-dien-3β-ol, and 27-nor-24-methylcholesta-5,22E-dien-3β-ol. Terrigenous lipids from the Changjiang River did not play a significant role in TSM since they were transported mainly southward. The sedimentary composition of these lipids showed a significant depletion of planktonic compounds in relation to other organic molecules. A comparison of these planktonic hydrocarbons in TSM and in sediments showed that degradation is in the following order: n-C 21:6 > n-C 19:1, n-C 19, and n-C 17 > n-C 18, pristane, and squalene. A similar comparison for the alcohols showed the following degradation trend: C 20:1 and C 22:1 n-alkenols > phytol. Carbon preference indices (CPIs) of suspended matter varied from 1.04 to 1.82 (average 1.41), and those of sediment ranged between 1.82 and 3.74 (average 2.81), reflecting higher contributions of the more refractory higher plant n-alkanes in the sediments.