近160年来闽浙泥质区游离态脂肪酸的分布特征及其环境指示意义

DISTRIBUTION PATTERN OF FREE FATTY ACIDS AND ITS IMPLICATIONS FOR ENVIRONMENT OVER THE LAST 160 YEARS IN THE ZHEJIANG-FUJIAN COASTAL MUD AREA

闽浙泥质区沉积物中的有机质来源复杂，记录着自然气候环境演变和人类活动的大量信息。本研究对该泥质区2站位岩芯中脂类生物标志物——游离态脂肪酸近160年来的分布特征进行对比分析，发现其沉积物样品游离态脂肪酸均以微藻类和细菌等海洋自生生物源为主，陆源高等植物贡献较少。结果进一步表明，东亚季风、黑潮和太平洋十年涛动（PDO）等自然气候环境因素变化主导了海源游离态脂肪酸总量：20世纪明显高于19世纪，20世纪70年代末至90年代初异常发育；长江全流域洪水事件（1998年、1954年和1931年）致使该泥质区陆源游离态脂肪酸异常增加，海源则减少。人类活动则主导了20世纪60年代之后游离态脂肪酸的持续增加，尤以海源增加最为显著；长江三峡大坝建设影响了硅藻的生长。i-C15：0%指标反演该泥质区的低氧程度20世纪50年代后呈显著增加趋势，80年代中期后进一步加剧。

The Zhejiang-Fujian coastal mud, a typical muddy deposit off the East Chinese continent, is a complex sink of organic matters sourced from both the Changjiang River and the western Pacific, which carry a large amount of information on climatic changes and anthropogenic activities. Lipid biomarkers, such as free fatty acids, produced by plants, algae, phytoplankton and bacteria have been used increasingly to identify the specific sources of organic matter in marine sediments. The distribution pattern of free fatty acids over the last 160 years in the sediment cores-DZ-28（28.63°N, 122.36°E; water depth 52.8 m）, and DZ-41（28.07°N, 121.95°E; water depth 42.2 m）-from Zhejiang-Fujian coastal mud area is investigated in the present paper. Results show that the free fatty acids are dominated by the marine autochthonous fatty acids derived from planktonic and bacterial sources, and followed by a small amount of allochthonous higher plant-derived fatty acids from the land. In response to the changes in the intensities of the East Asia Monsoon, the Kuroshio intrusion and the Pacific Decadal Oscillation phase, the amounts of marine free fatty acids are significantly higher in the 20th century than those in the 19th and abnormally high values found in the period from the late 1970s to early 1990s. Meanwhile, heavy floods（such as those in 1998,1954 and 1931 mentioned in literatures）from the whole of the Changjiang River catchment may lead to the sharp increase in terrestrial higher plant-derived free fatty acids instead of the decrease in marine autochthonous free fatty acids. Furthermore, human activities have become the dominating factor that caused the durative increase in total free fatty acids in particular the marine autochthonous ones since the late 1960s. Our study based on the indicators of free fatty acid further reveals that the construction of the Three Gorges Dam has inhibited to certain extent the growth of diatoms, and the i-C15：0% can be used effectively to invert the history of the hypoxia events in this mud area. The low-oxygen events have been in a trend of increase since 1950s followed by a more dramatic one after the 1980s.