Environmental changes in the lower reaches of Yellow River area during the last 1200 years revealed by multiple proxies from the Lake Liangshanpo

Abstract

利用梁山泊670 cm柱状岩芯沉积物，基于精确的AMS-¹⁴C年代测定，通过高分辨率的粒度、磁化率、总有机碳、C/N比值等环境代用指标的综合分析，并结合历史文献记载，初步揭示了1200 a来黄河下游地区平原湖泊沉积特征及环境演化历史.结果表明，梁山泊环境演化大致分为5个阶段：790940 AD期间，为低湖面的沼泽沉积环境，气候冷干；9401215 AD期间，屡次受到黄河决溢洪水影响，湖盆扩张，湖泊水位上升，为梁山泊极盛期，气候暖湿；12151310 AD期间，黄河夺淮入黄海，湖区淤积严重，湖泊萎缩减小；13101470 AD期间，再次受到黄河决溢洪水影响，水位上升，面积扩张，但逊于极盛期；1470 AD至现代，黄河河道进一步南移，远离梁山泊，湖盆淤积抬高，梁山泊最终消失，直到1855 AD，黄河第6次大改道北移，湖泊再次受到黄河洪水影响，由于前期受到泥沙淤积抬高，该地区仅作为黄河泥沙承载区.在气候变化大背景下，黄河改道决溢是梁山泊演化的主因.;A 670-cm-long sediment core from Lake Liangshanpo, a waterbody used to connect to the Yellow River, was analyzed to understand environmental changes in the lower reaches of Yellow River area during the late Holocene. Based on AMS-¹⁴C dating and the integration of high-resolution multi-proxy records such as grain size, magnetic susceptibility, total organic carbon, and C/N as well as historical documents, we infer that the lake has experienced five distinct phases of environment evolution during the last 1200 years. Our results show that a low lake-level stand with a wetland environment prevailed during 790-940 AD under dry and cold climate conditions. Then during 940-1215 AD, the lake expanded and reached to the maximum depth due to the flooding of the lower Yellow River (LYR) under relatively warm and wet climate conditions. In 1215-1310 AD, the lake began siltation likely due to the southward displacement of the Yellow River, experienced rapidly shrunk and a wetland environment. During 1310-1470 AD, the lake expanded due to the flooding of the LYR again, albeit the area is smaller than that of the maximum phase. From AD 1470 to the present, rapid siltation corresponding to the further southward displacement of the Yellow River especially in 1494 AD and until 1855 AD flooding events occurred when the channel of the LYR shifted back and the river discharged to the Bohai Bay. In sum, under the background of climate change, the avulsion and levee breaches of the LYR are the major reason for the environmental evolution of Lake Liangshanpo.