Abstract:

1,15-C30 (ω16) and 1,15-C32(ω18) alkyl diols and ketools were identified in Site4B sediment (65300 cm below the seafloor) from the Pearl River Mouth Basin, and the total contents of diols and ketools were distributed from 0.0264.373 μg/g dry sediment and 0.0051.549 μg/g dry sediment, respectively. The carbon isotope compositions were substantially enriched in 13C for 1,15-C30 diol (δ13C=-26.6‰±0.9‰) relative to the nC30 alkanol (δ13C=-32.8‰±1.5‰), suggesting the absence of terrigenous higher plants. Either the absence of high abundance of sedimentary sterols relative to longchain alkyl diols and ketodiols or the undetectability of these biomarkers in the surface sediment (065 cm) indicates that eustigmatophyceae was not a potential source, since the location of Site4B sediment was on the continental slope where nutrition salinity is so poor that it is not suitable for algae. δ13C of 1,15-C30 diol(-24.6‰-28.4‰) is similar to that of short chain nfatty acid (-25.5‰-28.6‰) in the sediment and revealed the same source as marine bacteria. In addition, the ketools have similar sources as diols or they are produces from different organisms but having strong couplings with each other; the ketools were not from the oxidization of the corresponding diols because the ketools ratios in the oxidized sediment (6595 cm) showed no significantly high values. The diol indices and ketool indices in the sediment having similar patterns, combined with the contents of these biomarkers, suggested the impact of the monsoon climate of South China Sea and the fresh water. Both the high diol indices and high diol concentration and the low diol indices and low diol concentration reflect the dominant impact of sea surface temperature, while the low diol indices and high diol concentration implied the major factor of increased intrusion of fresh water.

Key words:  Pearl River Mouth Basin, longchain alkyl diols, longchain alkyl ketools, diol indices, ketool indices