Sedimentary n-alkanes, their hydrogen isotopes, GDGTs and d15N as well as δ¹³Corg of lake Nam Co, Tibet@en

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）这一当前间冰期的过渡阶段，是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（Nam Co）为研究区域，探讨印度洋夏季风（Indian Ocean Summer Monsoon, IOSM）与西风带（Westerlies）之间的相互作用，以厘清气候系统变化对生态系统的影响。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dD、有机碳同位素比值δ¹³Corg以及氮同位素比值δ¹⁵N——重建区域环境与水文变化过程。基于本研究的古水文dD代用指标结果，由于特定的生态阈值效应，水生生物信号相较于陆地信号存在滞后性；而除气候变化外，这类生态阈值亦会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、湖水pH值与营养盐可获得性共同调控。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，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适用于印度洋夏季风的可靠代用指标。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，较高的太阳辐射量可形成显著的海陆气压梯度，伴随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，较弱的太阳辐射量则推动西风带活动增强，进而使其对青藏高原的影响范围扩大。本研究结果有助于阐明印度洋夏季风的演化特征与变异性，同时揭示了从末次冰期至全新世间冰期阶段，湖泊系统的pH值、δ¹³Corg及δ¹⁵N均发生了显著变化。