LAKE QINGHAI, CHINA - CLOSED-BASIN LAKE LEVELS AND THE OXYGEN ISOTOPE RECORD FOR OSTRACODA SINCE THE LATEST PLEISTOCENE
LAKE QINGHAI, CHINA - CLOSED-BASIN LAKE LEVELS AND THE OXYGEN ISOTOPE RECORD FOR OSTRACODA SINCE THE LATEST PLEISTOCENE
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DOI：
10.1016/0031-0182(91)90041-o
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发表时间：
1991-05-01
影响因子：
3
通讯作者：
NIESSEN, F
中科院分区：
文献类型：
--
作者：
LISTER, GS;KELTS, K;NIESSEN, F
1985年，中瑞联合对中国最大的内陆湖泊青海湖进行了湖泊地质考察，获得了青藏高原北方末次盛冰期以来季风和日射变化的地震剖面和活塞岩心，用于校正古气候模型。青海湖是一个面积为4278平方公里（1985年），海拔3194米的常年湖泊。000平方公里的集水区附近的西北角的高原。 26.5米深的终端湖（1985年），含微咸、碱性、富含硫酸镁的沃茨（14 g l-1 TDS），自末次冰期以来没有溢出，但其水位对气候和水文变化作出了反应。海底沉积物结构的地震反射剖面显示了复杂的地形，有水道、残留阶地、在一个4-6米的主要为平层沉积物的包裹体下，发现了沉积物的构造倾斜和变形。 最底层的岩芯（约14,500年B. P.）主要包括在寒冷干旱的气候条件下，在一个几米深的较小的洪泛平原湖泊中沉积的水成黄土。 AMS放射性碳测年结果表明，青海湖中部地区晚更新世和全新世沉积物的平均沉积速率约为0.3-0.5 mm/yr。介形类化石的δ-O-18值记录了青海湖沃茨同位素组成的变化，这种变化可能与降水-蒸发平衡有关，而降水-蒸发平衡控制了青海湖的古水位。 青海湖地区的降水/蒸发平衡很大程度上取决于亚洲季风系统。青海湖沉积记录表明，冰后期冰川融水没有大量涌入湖盆。 该区域的气候一直保持干旱，直到至少约12,500年B. P.，季风可能开始的时候。 河流输送的泥沙在约11,800年B. P.时首次到达盆地中心，当湖的深度可能增加到大约5米时。 在大约10，800年B. P.（欧洲，新仙女木）之后的几个世纪，季风可能减弱，导致了进一步的干旱期。 在大约10，200年B. P.的盆地开始填充向现代湖泊的尺寸，以响应亚洲季风的永久加强。 在大约10，200 -9800年、9500-8500年、8300-7200年B. P.以及大约6800年B. P.的一个世纪期间，湖平面可能显著上升。 通过中期全新世气候最佳的短期湖泊水位波动是最小的，表明一个非常稳定的气候/水文制度。 自3000 +/- 500 yr B. P.以来，湖泊沃茨的同位素稳定状态掩盖了气候/水文状况依赖的三角洲O-18梯度，但几乎没有地层学证据表明，自那时以来，湖泊水位已明显低于其目前的水平。 湖水的三个负的δ-O-18漂移可能对应于中国新冰期期间约3000、2000和1500年B. P.高原上已知的冰川前进。
In 1985 a Sino-Swiss limnogeological expedition to China's largest inland lake recovered seismic profiles and piston cores to help calibrate palaeoclimatic models of monsoon and insolation fluctuations over the northern Tibet-Qinghai Plateau since the Last Glacial Maximum.Lake Qinghai, a perennial lake with an area of 4278 km2 (1985) at 3194 m above sea level, receives drainage from 30,000 km2 of catchment near the northwest corner of the Plateau. The 26.5m deep terminal lake (1985), with brackish, alkaline, magnesium-sulphate rich waters (14 g l-1 TDS), has not overflowed since the last Glacial, but its level have responded to climatic and hydrologic changes.Seismic-reflection profiles for the sub-bottom sediment structures revealed a complex topography with channels, relict terraces, tectonic tilting and deformation in deposits buried under a 4-6 m packet of mainly flat-bedded sediments from which core samples were recovered. The lowermost cored material (approximately 14,500 yr B.P.) comprises mainly water-lain loess deposited in a smaller flood-plain lake of up a few metres depth under cold arid climatic conditions. AMS radiocarbon dating indicates average sedimentation rates for latest Pleistocene and Holocene deposits in central basin regions of approximately 0.3-0.5 mm yr-1.The delta-O-18 values of fossil ostracod valves provide a record of changes in the isotopic chemistry of the lake waters that can be related to the precipitation: evaporation budgets which have controlled the palaeo-levels for Lake Qinghai. The precipitation/evaporation budget for the Lake Qinghai region is largely determined by the Asian monsoon system.The Lake Qinghai sediment record shows that there was no large influx of glacier melt-waters into the lake basin during the post-Glacial. The regional climate remained arid until at least approximately 12,500 yr B.P., when an incipient monsoon was possibly initiated. River-transported silts first reached the basin centre at approximately 11,800 yr B.P., when the lake depth may have increased to approximately 5 m. Possibly a monsoonal weakening for several centuries after approximately 10,800 yr B.P. (Europe, Younger Dryas) caused a further period of aridity. At approximately 10,200 yr B.P. the basin began filling towards modern lake dimensions in response to a permanent strengthening of the Asian monsoon. Substantial lake-level rises probably characterised the periods approximately 10,200-9800, 9500-8500, 8300-7200 yr B.P. and through perhaps a century at about 6800 yr B.P. Decreasing levels probably characterised the intervening intervals. Short-term lake-level fluctuations through the mid-Holocene climatic optimum were minimal, indicating a very stable climatic / hydrologic regime. An isotopic steady-state for the lake waters since 3000 +/- 500 yr B.P. obscures the climatic / hydrologic regime dependent delta-O-18 gradient, but there is little stratigraphic evidence to suggest that the lake level has been significantly below its present level since that time. Three negative delta-O-18 excursions for the lake water may correspond to known glacier advances on the Plateau at approximately 3000, 2000 and 1500 yr B.P. during China's neoglacial.