青藏高原北部库赛湖沉积柱中长链烯酮的分布特征及古环境意义

长链烯酮不饱和度指标U37K或U37K′已被广泛应用于古海洋表层水温的重建,但用于恢复湖泊古温度的研究则相对很少。本文以青藏高原北部咸水湖泊库赛湖作为研究对象,对湖心一个5m沉积柱中的长链烯酮进行了测定分析,并通过分子生物学手段确定了其母源。结果表明该沉积柱的大部分层位存在长链烯酮,其C37/C38<1;DNA测序结果表明库赛湖中的定鞭藻为Isochrysis属,为长链烯酮的母源。根据已发表文献中的湖泊环境中长链烯酮不饱和度指标U37K与温度的经验公式估算出的古湖水温度接近于实测的现代夏季水温,且与甘油二烷基甘油四醚(Glycerol Dialkyl Glycerol Tetraethers,GDGT)重建的库赛湖古湖水温度范围基本一致。但是,用长链烯酮恢复的古湖水温度总体上稍高于由GDGT计算出的温度且波动更为强烈,这可能与这两种脂类的母源生物在湖中的栖息层位不同有关。

Distribution of Long-chain Alkenones and their Implications for Paleoenvironment from a Sediment Core of Kusai Lake, Northern Tibetan Plateau

The long-chain alkenone (LCA) unsaturation proxies U₃₇^K or U₃₇^K'' have been widely applied for reconstructing past sea surface temperatures, but there are fewer studies on their applications in lacustrine system. Here we studied the distribution of LCA in a 5-m sediment core from the Kusai Lake, northern Tibetan Plateau, and the LCA-producing algae were determined by molecular biology methods. Results showed that LCA existed in most subsamples of the core with the ratio of C³⁷/C³⁸<1. The dominant haptophyte in the sediment core was closely related to Isochrysis according to DNA sequencing result, which was the LCA producer in the Kusai Lake. Base on the published temperature calibration of U₃₇^K for lacustrine environment, the estimated paleo-lake water temperatures were close to the modern lake summer water temperature, and in accordance with the range of reconstructed paleotemperatures from Glycerol Dialkyl Glycerol Tetraethers (GDGT). However, in general the LCA-derived temperatures were slightly higher than the GDGT-derived temperatures, which is probably due to the fact that the organisms producing the two groups of lipids lived at different depths of the lake water column.