Diatom analysis was applied to a 5.56-m-long sediment core, spanning the last 7.8 ka, from Lake Chenghai on the southeastern margin of the Tibetan Plateau. Diatom assemblages are dominated by Cyclotella rhomboideo-elliptica, Cyclostephanos dubius and small fragilarioid and periphytic taxa. These diatom taxa are interpreted to be sensitive to changes in trophic status and/or turbulence of the water column that are probably related to variations in precipitation and temperature induced through the Asian monsoon. High abundances of C. dubius, Staurosirella pinnata and periphytic taxa suggest higher trophic status (mesotrophic) and stronger turbulence in the water column in the middle Holocene (7.8-4.5 ka BP). During the period of 4.5-2.3 ka BP, a decline in C. dubius, S. pinnata and periphytic taxa, and an increase in C. rhomboideo-elliptica with the appearance of Cyclotella ocellata suggests a response to decreasing trophic level (more oligotrophic). After 2.3 ka BP, the persistent increases in C. rhomboideo-elliptica and the loss of Cyclotella ocellata mirrored a further decrease in trophic level (oligotrophic). The main changes in the diatom assemblages in the Lake Chenghai sediment core reflect direct and indirect climate forcing and in particular, the strength of monsoonal precipitation, which in turn corresponds to orbitally induced variability in Northern Hemisphere summer solar insolation since 7.8 ka BP.
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机译:将硅藻分析应用于一个青藏高原东南缘澄海湖,长5.56米的沉积岩心,跨越最后7.8 ka。硅藻的组合主要由椭圆形的小摆线菌,双环的Cyclostephanos dubius和小型的脆弱类和附生类群组成。这些硅藻类群被解释为对水柱的营养状态和/或湍流敏感,这可能与亚洲季风引起的降水和温度变化有关。高浓度的杜比梭菌,梭状葡萄球菌和周围植物类群表明中全新世(7.8-4.5 ka BP)中水柱的营养状态(中营养)和湍流更强。在4.5-2.3 ka BP期间,杜比梭菌,梭状芽胞杆菌和周生生物类群的减少以及菱形梭状芽孢杆菌的增加以及小圆盘菌的出现表明对营养级降低(低养分)有所响应。在2.3 ka BP后,菱形衣原体的持续增加和卵圆环菌的损失反映了营养水平的进一步降低(贫营养)。澄海湖沉积物中硅藻组合的主要变化反映了直接和间接的气候强迫,特别是季风降水的强度,这又对应于自7.8 ka BP以来北半球夏季日照的轨道诱发变化。
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