Abstract

Climate changes on the Southwest coast of India have essential impacts on social and economic development, and the ecosystem of Southern India. Here, we present the last 2000 cal yr AD rare earth elemental records of the sediment core from the Cherai, Kerala coast, southwest India. The light rare earth elements (LREE) were the most abundant fraction in the core sediment, followed by medium rare earth elements (MREE) and heavy rare earth elements (HREE). Total REE (ΣREE) showed a significant correlation with fine fractions and Y, Al, Ti, Fe and total organic carbon content of the sediments, suggesting an intrinsic relationship between REE, total organic carbon and fine grain-size fraction. The LREE and MREE were enriched over the MREE due to their high adsorption with the fine fraction. The lack of correlation between terrigenous elements and low Y/Ho elemental ratio suggests a minor shift in the source materials. High ΣREE values during warm (Medieval Warm Period/ Medieval Climate Anomaly (MWP/MCA) and cold Little Ice Age (LIA) periods indicate a high influx of lithogenous materials during these intervals. The negative δCe values except MCA suggest a suboxic condition and the δEu values suggest feldspar-rich source rock material derived from moderately weathered sediments. It also indicates that the REE variations are controlled by factors like river supply, biological productivity and redox condition. A close link between monsoonal precipitation and REE records existed on the southwest coast of India. During the Dark Age Cold Period (DACP)/MWP transition, a sudden increase in monsoon is documented and the monsoon precipitation was further decreased during LIA and Current Warming Period. The Cherai core REE records synchronize with the episodes of centennial-scale warm/cool events and essentially follow the northern hemispheric climate cycles.

摘要

印度西南海岸的气候变化对社会和经济发展以及印度南部的生态系统具有重要影响。在这里，我们展示了印度西南部喀拉拉邦海岸 Cherai 沉积岩心的最后 2000 年公元稀土元素记录。轻稀土元素 (LREE) 是岩心沉积物中最丰富的部分，其次是中稀土元素 (MREE) 和重稀土元素 (HREE)。总稀土元素 (ΣREE) 与沉积物的细粒级分和 Y、Al、Ti、Fe 和总有机碳含量显着相关，表明稀土元素、总有机碳和细粒度级分之间存在内在关系。LREE 和 MREE 比 MREE 富集，因为它们对细小部分具有高吸附性。陆源元素与低 Y/Ho 元素比之间缺乏相关性表明源材料发生了微小的变化。温暖时期（中世纪暖期/中世纪气候异常 (MWP/MCA) 和寒冷的小冰期 (LIA) 期间的高 ΣREE 值表明在这些时间段内岩质物质大量涌入。除 MCA 外的负 δCe 值表明低氧条件和δEu 值表明来自中度风化沉积物的富含长石的烃源岩材料。这也表明稀土元素的变化受河流供应、生物生产力和氧化还原条件等因素的控制。西南沿海季风降水与稀土元素记录之间存在密切联系印度。在黑暗时代寒冷时期 (DACP)/MWP 过渡期间，记录了季风突然增加，季风降水在 LIA 和当前变暖期进一步减少。Cherai 核心 REE 记录与百年尺度的暖/冷事件同步，基本上遵循北半球气候周期。