Sedimentary n-alkanes, their hydrogen isotopes, GDGTs and d15N as well as d13Corg of lake Nam Co, Tibet

The transition from the last Glacial to the current Interglacial, the Holocene, represents an important period with climatic and environmental changes impacting ecosystems. In this study, we examined the interplay between the Indian Ocean Summer Monsoon (IOSM) and the Westerlies at lake Nam Co, southern Tibet to understand the climatic effects on the ecosystem. Different organic geochemical proxies (n-alkanes, glycerol dialkyl glycerol tetraethers, dD, d13Corg, d15N) are applied to reconstruct the environmental and hydrological changes on one of the longest available paleorecords at the Tibetan Plateau. Based on our paleohydrological dD proxies, the aquatic signal lags the terrestrial one due to specific ecological thresholds, which, in addition to climatic changes, can influence aquatic organisms. The aquatic organisms' response strongly depends on temperature and associated lake size, as well as pH and nutrient availability. Because the terrestrial vegetation reacts faster and more sensitively to changes in the monsoonal and climatic system, the dD of n-C29 and the reconstructed inflow water signal represent an appropriate IOSM proxy. In general, the interplay of the different air masses seems to be primarily controlled by solar insolation. In the Holocene, the high insolation generates a large land-ocean pressure gradient associated with strong monsoonal winds and the strongest IOSM. In the last glacial period, however, the weak insolation promoted the Westerlies, thereby increasing their influence at the Tibetan Plateau. Our results help to elucidate the variable IOSM, and they illustrate a remarkable shift in the lake system regarding pH, d13Corg and d15N from the last glacial to the Holocene interglacial period.

末次冰期向全新世（Holocene）这一现代间冰期的过渡阶段，是一段气候与环境变化深刻影响生态系统的重要时期。本研究以藏南纳木错湖为研究对象，探讨印度洋夏季风（Indian Ocean Summer Monsoon, IOSM）与西风带之间的相互作用，以厘清气候系统变化对区域生态系统的影响。本研究依托青藏高原现存最长的古气候记录之一，采用多种有机地球化学代用指标——包括正构烷烃（n-alkanes）、甘油二烷基甘油四醚（glycerol dialkyl glycerol tetraethers）、氢同位素比值δD、有机碳同位素δ¹³Corg以及氮同位素δ¹⁵N——重建区域环境与水文变化历史。基于古水文δD代用指标的分析结果显示，水生生物信号滞后于陆地信号，这一现象源于特定的生态阈值；除气候变化外，生态阈值亦可对水生生物产生影响。水生生物的响应程度主要受温度及对应湖泊规模、水体pH值与养分可获得性共同调控。由于陆地植被对季风与气候系统变化的响应更为快速且敏感，因此正构烷烃n-C₂₉的氢同位素比值及重建的入湖水信号可作为可靠的印度洋夏季风代用指标。总体而言，不同气团间的相互作用主要受太阳辐射量调控。在全新世时期，高太阳辐射量会形成显著的海陆气压梯度，驱动强劲的季风环流与最强盛的印度洋夏季风活动。而在末次冰期，较弱的太阳辐射则促进了西风带的增强，进而提升了其对青藏高原的影响程度。本研究结果有助于阐明印度洋夏季风的变化特征，同时揭示了从末次冰期至全新世间冰期阶段，纳木错湖系统在pH值、δ¹³Corg及δ¹⁵N等指标上发生的显著转变。