A 14 ka high-resolution delta O-18 lake record reveals a paradigm shift for the process-based reconstruction of hydroclimate on the northern Tibetan Plateau
A 14 ka high-resolution delta O-18 lake record reveals a paradigm shift for the process-based reconstruction of hydroclimate on the northern Tibetan Plateau
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14ka高分辨率三角洲O-18湖泊记录揭示了青藏高原北部基于过程的水文气候重建的范式转变
DOI：
10.1016/j.quascirev.2018.09.040
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发表时间：
2018
影响因子：
4
通讯作者：
Hoelzmann Philipp
中科院分区：
文献类型：
--
作者：
Wuennemann Bernd;Yan Dada;Andersen Nils;Riedel Frank;Zhang Yongzhan;Sun Qianli;Hoelzmann Philipp
中纬度西风带（MLW）与亚洲夏季风（ASM）在青藏高原（TP）的竞争的影响仍然是一个讨论的问题，如何以及在何种程度上这两个大气系统一直在控制水文气候在全新世。湖泊沉积物中的耗尽氧同位素通常被解释为夏季季风水分供应增强，这意味着迁移的ASM深入到高原内部全新世时期。为了测试这种关系，我们使用了高分辨率的氧同位素记录（平均20年的分辨率）结合碳酸盐和矿物相，钛通量，粒度和介形虫丰度来自一个6.84米长的沉积物芯在内陆库海湖盆地，东北TP。结果表明：1）在过去14 ka中，δ 18 Ocarb与总碳酸盐之间存在持续的正协方差，表明湖泊水和相应碳酸盐降水的数十年至百年尺度的同位素特征具有主导的季节性影响; 2）外来沉积物通量与δ 18 Ocarb之间存在负协方差（和碳酸盐），这归因于非夏季通量率的相对增加; 3）湖平面变化与碳酸盐矿物相态和介形虫组合的出现/消失的对应关系，（4）塔里木盆地各湖记录中ASM控制的和MLW控制的同位素特征之间的反向关系。库海湖沉积物中δ 18 Ocarbin的富集主要是夏季高蒸发的结果，而ASM相关的降雨量并没有发挥重要作用，可能被不同水源的同位素特征所抵消。相反，亏损δ 18 Ocarb主要归因于非夏季较冷温度期间的供水和MLW来源的同位素特征普遍较轻。这一发现可能会导致一个范式转变，以这种方式，亏损δ 18 O的碳酸盐主要不是由于ASM相关的降雨，如以前所假设的。重建的库海湖水文气候历史表明，在新仙女木期（12.8-11.5 ka），在非常浅的池塘状条件下，西源气候占主导地位。尽管在全新世早期（11.5-7.5 ka）气候改善，水文条件仍然不稳定，夏季和冬季的优势之间的频繁交替。在全新世中期（7.5-5.5 ka）的湖泊经历了最高的湖泊水位主要是夏季风相关的供水，分配到全新世水文气候最佳。频繁的高振幅波动之后（5.1-2.9 ka）是指冷却/干燥事件下增强MLW的影响伴随着强烈的湖平面下降。晚全新世（2.9ka-今）经历了中等的同位素变化和湖平面波动，δ 18 O_（18）C_（1与来自北大西洋流冰和融水排放的冷却事件的高对应性表明与跨越TP的MLW传输的北方半球气候的密切联系。
The influence of the mid-latitude westerlies (MLW) competing with the Asian summer monsoons (ASM) over the Tibetan Plateau (TP) remains a matter of discussion on how and to which extent both atmospheric systems have been controlling hydro-climate during the Holocene. Depleted oxygen isotopes in lake deposits were commonly interpreted in terms of enhanced summer monsoon moisture supply, implying a migration of the ASM deep into the interior of the plateau during Holocene periods. In order to test this relationship we used a high resolution oxygen isotope record (mean 20 yr resolution) in combination with carbonates and mineral phases, titanium flux, grain size and ostracod abundances derived from a 6.84 m long sediment core in the endorheic Kuhai Lake basin, north-eastern TP. The results confirm 1) continuous positive co-variance between enriched δ18Ocarband total carbonates during the last 14 ka, indicative of dominant seasonal influence on multi-decadal to centennial scale isotopic signatures in lake water and respective carbonate precipitation, 2) negative co-variance between allochthonous sediment flux and δ18Ocarb(and carbonates) attributed to relative increase of flux rates during non-summer seasons, 3) correspondence of lake level variations with carbonate mineral phases and the occurrence/disappearance of ostracod assemblages, and 4) inverse relationships between isotopic signatures in ASM-dominated and MLW-controlled lake records across the TP. Enriched δ18Ocarbin Kuhai Lake sediments was primarily a result of high evaporation during the summer seasons, while ASM-related rainfall amount did not play an important role, likely counterbalanced by isotopic signatures from different water sources. Conversely, depleted δ18Ocarbwas mainly attributed to water supply during non-summer seasons of colder temperatures and generally light isotopic signatures from MLW-derived sources. This finding may lead to a paradigm shift in such way that depleted δ18O in carbonates is primarily not the result from ASM-related rainfall as previously assumed. The reconstructed hydro-climatic history of Kuhai Lake indicates the dominance of westerly-derived climate during the Younger Dryas interval (12.8–11.5 ka) under very shallow pond-like conditions. Despite climate amelioration during the early Holocene (11.5–7.5 ka) hydrological conditions remained unstable with frequent alternations between dominance of summer and winter seasons. During the middle Holocene (7.5–5.5 ka) the lake experienced highest lake levels dominated by summer monsoon-related water supply, assigned to the Holocene hydro-climatic optimum. Frequent high-amplitude fluctuations afterwards (5.1–2.9 ka) refer to cooling/drying events under enhanced MLW influence accompanied by a strong lake level decline. The late Holocene (2.9 ka- Present) period experienced moderate isotopic variations and fluctuating lake levels in response to variable influence of summer- or winter-related hydro-climatic conditions.This seesaw-like pattern with amplitudes of >10‰ in δ18Ocarbresembles fluctuations in cave records and variations between air and seawater (Dole effect). High correspondence with cooling events derived from North Atlantic drift ice and meltwater discharge indicate close ties to northern hemispheric climate transmitted by the MLW across the TP.