The grain size endmembers of Tengchongbeihai wetland sediments over the past 46 ka

Here, we present a grain size end-member analysis for Tengchongbeihai wetland sediments from southwestern China to investigate the paleo-hydroclimate changes since the late MIS3. The overall low fine silt (EM2) content before ~16.5 cal ka BP resulted from weak catchment erosion indicating weak ISM during cold glacial while the increasing trend thereafter indicates the ISM strengthened during the last deglaciation and Holocene. Such an orbital ISM evolution resembles to the insolation gradient between 25°N and 25°S during the boreal summer periods, which implies the transequatorial insolation difference could be an alternative explanation for the orbital scale low latitude hydroclimate changes. The striking peaks of coarse component (EM3) around ~12, 16, 24, 29, 32 and 39 cal ka BP were related to significant water level descending indicating the millennial ISM collapse corresponding to the YD and Heinrich events. However, the absence of sawtooth feature as the NGRIP δ18O and the well correspondence to the Indian Ocean sea surface temperatures (SSTs) of the ISM collapses evidence the complementary role of low latitude climate for the North Atlantic climate on the millennial scale hydroclimate variabilities.本研究针对中国西南腾冲北海湿地的沉积物开展粒度端元分析（grain size end-member analysis），旨在探究深海氧同位素3期（Marine Isotope Stage 3, MIS3）晚期以来的古水文气候变化。约16.5校准千年距今（cal ka BP）之前，细粉砂组分（EM2）整体含量偏低，其成因源于汇流域侵蚀作用较弱，反映了寒冷冰期阶段印度夏季风（Indian Summer Monsoon, ISM）活动偏弱；而此后该组分含量的持续上升趋势，则指示末次冰消期及全新世期间印度夏季风强度逐步增强。这种轨道尺度的印度夏季风演化特征，与北半球夏季25°N与25°S之间的日照辐射梯度高度相似，这意味着跨赤道日照辐射差或可作为轨道尺度低纬度水文气候变化的另一解释机制。粗颗粒组分（EM3）在约12、16、24、29、32及39校准千年距今（cal ka BP）附近出现显著峰值，这与水域水位大幅下降密切相关，指示了对应新仙女木事件（Younger Dryas, YD）与赫里里奇事件（Heinrich events）的千年级印度夏季风崩溃事件。不过，与北格陵兰冰芯项目（North Greenland Ice Core Project, NGRIP）的δ¹⁸O记录所呈现的锯齿状特征不同，且印度夏季风崩溃事件与印度洋海表温度（sea surface temperatures, SSTs）记录高度契合，这表明在千年级尺度的水文气候变率中，低纬度气候对北大西洋气候起到了补充调控作用。