Rapid northwestward extension of the East Asian summer monsoon over the last deglaciation: evidence from mollusk record

The magnitude and rate of spatial expansion of the East Asian summer monsoon (EASM) rain belt as the climate warms remains unclear. Existing assessments still lack the ecological records that are more sensitive to the EASM rainfall to quantify the spatial extension during the past warming scenarios. Here, the spatiotemporal extension of EASM intensity since the last glacial maximum (LGM) is reconstructed using six well-dated mollusk fossil sequences from Chinese loess sections located at the northern part of the EASM. The abundant occurrence of typical dominant mollusk species indicative of EASM intensity gradually delayed from southeast to northwest since the last deglacial warming. The estimated expansion rate of EASM intensity accelerated markedly during the ~12-9 ka (~50 km/ka), which corresponded with the early-Holocene rapid warming period, shifting northwestward ~150 km compared to present. This imply that northern fringe of EASM in northern China will become wetter as the climate warms.

Methods
The dataset was collected at the Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China. The mollusk fossils were picked and identified under a binocular microscope, and counted their abundance to produce a MS.

气候变暖背景下，东亚夏季风（East Asian summer monsoon, EASM）雨带的空间扩张幅度与速率仍不明确。现有研究仍缺乏对东亚夏季风降水更为敏感的生态记录，难以量化过去变暖情景下的雨带空间扩张范围。本研究依托采自东亚夏季风北缘中国黄土剖面的6条高精度定年软体动物化石序列，重建了末次冰盛期（last glacial maximum, LGM）以来东亚夏季风强度的时空扩张特征。自末次冰消期变暖以来，指示东亚夏季风强度的典型优势软体动物类群的大量出现位点，呈现出从东南向西北逐渐滞后的分布规律。估算得到的东亚夏季风强度扩张速率在约12~9 ka（千年）期间显著加快（约50 km/千年），这一时期与早全新世快速变暖阶段相吻合，此时东亚夏季风北界较现代向西北推进了约150 km。本研究结果表明，随着气候持续变暖，中国北方地区的东亚夏季风北缘区域将趋于湿润。

研究方法
本数据集采集于中国科学院地质与地球物理研究所新生代地质与环境重点实验室（北京 100029，中国）。软体动物化石经双目显微镜挑选、鉴定，并统计其丰度以构建本数据集。