东海泥质区单体正构烷烃的碳同位素组成及物源分析 *

利用气相色谱(GC)和气相色谱/同位素比值质谱(GC/IRMS)对东海近岸泥质区、济州岛西南泥质区和冲绳海槽北部表层沉积物中正构烷烃的单体碳同位素组成及分布进行了分析。结果显示东海不同泥质区典型海洋藻类源正构烷烃C₁₉同位素组成基本相似,在-27.4 ‰ ~-28.0 ‰ 之间,平均为-27.7 ‰ 。典型海洋水生植物源C₂₃同位素组成在-28.5 ‰ ~-31.6 ‰ 之间,平均为-30.5 ‰ ,碳同位素组成从近岸泥质区到冲绳海槽北部逐渐变重,表明海槽区与陆架区海洋水生植物种类有所不同。陆架区长链正构烷烃(C₂₅~C₃₁)部分随着碳数的增加,其同位素组成逐渐变轻,但海槽区这一变化不大,显示陆架区的陆源高等植物蜡具有相似的物源,而冲绳海槽北部由于黑潮主干区和黑潮分支(对马暖流)对陆架沉积物进入深海的控制性阻隔作用,其物源与陆架区区别较大。现代输入东海的陆源植物以C₃植物为显著优势,C₃植物对近岸泥质区北部、近岸泥质区南部、远端济州岛西南泥质区和冲绳海槽北部陆源植物的贡献分别为83 % ,95 ％,75 % 和70 % 。

COMPOUND-SPECIFIC CARBON ISOTOPE COMPOSITIONS OF INDIVIDUAL n-ALKANES IN THE EAST CHINA SEA MUD AREAS

The molecular compositions and compound-specific stable carbon isotope compositions of individual n-alkanes from surface sediments of the East China Sea (ECS) mud areas including the coastal mud area, the southwest mud area to Cheju Island, and the Northern Okinawa Trough were analyzed using gas chromatography/mass spectrometry (GC/MS) and gas chromatography/isotopic ratio mass spectrometry (GC/IRMS). The results show that δ¹³ C values of C₁₉ originated from typical marine algae in the ECS mud areas are relatively similar, ranging from -27.4 ‰ to -28.0 ‰ with an average of -27.7 ‰ . The δ¹³ C values of C₂₃ originated from typical aquatic plant are between -28.5 ‰ to -31.6 ‰ with an average of -30.5 ‰ . This δ¹³ C value of C₂₃ generally increase from the shelf mud areas to the Northern Okinawa Trough, suggesting that aquatic plant categories of the mud areas in the shelf and Okinawa Trough are different. The δ¹³ C values of individual long-chain n-alkanes (C₂₅~C₃₁) decrease with the increase of carbon number in the shelf mud areas; while the difference of δ¹³ C values of different individual long-chain n-alkanes (C₂₅~C₃₁) in the Northern Okinawa Trough is small compared with those in the shelf mud areas. It is indicated that terrestrial higher plants lipids in the coastal mud area and southwest mud area to Cheju Island have a similar source, while the source in the Northern Okinawa Trough is somewhat different due to the obstruction of the Kuroshio Current and the Tsushima Warm Current for the transport of sediments from shelf into the Northern Okinawa Trough. The modern terrestrial higher plants into the East China Sea are dominant in C₃-type plants. The contributions of C₃-type plants to the northern coastal mud area, southern coastal mud area, southwest mud area to Cheju Island and Northern Okinawa Trough are 83 ％, 95％, 75％ and 70 ％ respectively.