Diatom response to Asian monsoon variability during the Holocene in a deep lake at the southeastern margin of the Tibetan Plateau
Diatom response to Asian monsoon variability during the Holocene in a deep lake at the southeastern margin of the Tibetan Plateau
复制标题
青藏高原东南缘深湖全新世硅藻对亚洲季风变化的响应
作者：
Li Yanling;Liu Enfeng;Xiao Xiayun;Zhang Enlou;Ji Ming
对青藏高原东南缘澄海5.56米长、横跨最后7.8千卡的沉积岩芯进行了硅藻分析。硅藻组合以菱形椭圆形环藻、杜氏环藻和小的脆弱类及周生类群为主。这些硅藻类群被认为对营养状态的变化和/或水柱的湍流很敏感，这可能与亚洲季风引起的降水和温度的变化有关。中全新世(7.8-4.5ka BP)水体中的高丰度OFC、Staurosirella pinnata和围生类群表明，水体处于较高的营养状态(中营养)和较强的湍流。在4.5-2.3Ka BP期间，杜比斯(S.dubius)、金针藻和周生类群的减少，菱形椭圆形分类群的增加(伴随着环藻的出现)，暗示着对营养水平下降(更少营养)的反应。2.3ka BP后，菱形椭圆体的持续增加和眼环藻的丧失导致营养水平的进一步下降(少营养)。澄海沉积核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，这反过来又对应于7.8ka BP以来北半球夏季太阳辐射的轨道诱导变化。
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 byCyclotella rhomboideo‐elliptica,Cyclostephanos dubiusand 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 ofC. dubius,Staurosirella pinnataand 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 inC. dubius,S. pinnataand periphytic taxa, and an increase inC. rhomboideo‐ellipticawith the appearance ofCyclotella ocellatasuggests a response to decreasing trophic level (more oligotrophic). After 2.3 ka BP, the persistent increases inC. rhomboideo‐ellipticaand the loss ofCyclotella ocellatamirrored 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.