Isotopic composition of terrestrial plant waxes (dD and δ¹³C of n-alkanes) of sediment core SO188_342 from the Northern Bay of Bengal for the last 18 ka

The Indian Summer Monsoon (ISM) is a major global climatic phenomenon. Long-term precipitation proxy records of the ISM, however, are often fragmented and discontinuous, impeding an estimation of the magnitude of precipitation variability from the Last Glacial to the present. To improve our understanding of past ISM variability, we provide a continuous reconstructed record of precipitation and continental vegetation changes from the lower Ganges-Brahmaputra-Meghna catchment and the Indo-Burman ranges over the last 18,000 years (18 ka). The records derive from a marine sediment core from the northern Bay of Bengal (NBoB), and are complemented by numerical model results of spatial moisture transport and precipitation distribution over the Bengal region. The isotopic composition of terrestrial plant waxes (dD and d13C of n-alkanes) are compared to results from an isotope-enabled general atmospheric circulation model (IsoCAM) for selected time slices (pre-industrial, mid-Holocene and Heinrich Stadial 1). Comparison of proxy and model results indicate that past changes in the dD of precipitation and plant waxes were mainly driven by the amount effect, and strongly influenced by ISM rainfall. Maximum precipitation is detected for the Early Holocene Climatic Optimum (EHCO; 10.5-6 ka BP), whereas minimum precipitation occurred during the Heinrich Stadial 1 (HS1; 16.9-15.4 ka BP). The IsoCAM model results support the hypothesis of a constant moisture source (i.e. the NBoB) throughout the study period. Relative to the pre-industrial period the model reconstructions show 20% more rain during the mid-Holocene (6 ka BP) and 20% less rain during the Heinrich Stadial 1 (HS1), respectively. A shift from C4-plant dominated ecosystems during the glacial to subsequent C3/C4-mixed ones during the interglacial took place. Vegetation changes were predominantly driven by precipitation variability, as evidenced by the significant correlation between the dD and d13C alkane records. When compared to other records across the ISM domain, precipitation and vegetation changes inferred from our records and the numerical model results provide evidence for a coherent regional variability of the ISM from the Last Glacial to the present.

印度夏季季风（ISM）是全球主要气候现象之一。然而，关于ISM的长期降水代用记录往往支离破碎且不连续，这阻碍了对从全新世到现今的降水变化幅度的估计。为了加深我们对过去ISM变化的理解，我们提供了一条从过去18,000年（18 ka）以来，下恒河-布拉马普特拉-梅格纳流域和印度-勃固山脉地区连续重建的降水及大陆植被变化记录。这些记录源自孟加拉湾北部（NBoB）的海洋沉积岩心，并由孟加拉地区的水分传输和降水分布的数值模型结果进行补充。对于选定的时间切片（前工业时期、中全新世和海因里希阶地1期），将陆地植物蜡的稳定同位素组成（正构烷烃的dD和d13C）与基于同位素的一般大气环流模型（IsoCAM）的结果进行比较。代用记录与模型结果的比较表明，过去降水和植物蜡中dD的变化主要受数量效应驱动，并受到ISM降水的强烈影响。在早期全新世气候最优期（EHCO；10.5-6 ka BP）检测到最大降水，而在海因里希阶地1期（HS1；16.9-15.4 ka BP）发生最小降水。IsoCAM模型结果支持了在整个研究期间水分来源恒定（即NBoB）的假设。与工业前时期相比，模型重建显示中全新世（6 ka BP）降水增加了20%，而在海因里希阶地1期（HS1）降水减少了20%。从冰期以C4植物为主的生态系统向间冰期后的C3/C4混合型生态系统转变。植被变化主要由降水变化驱动，正如dD和d13C烷烃记录之间的显著相关性所证明。将我们的记录和数值模型结果推断的降水和植被变化与ISM区域内的其他记录进行比较，提供了从全新世到现今ISM区域变异性一致性的证据。