南海西北部过去~55 ka以来元素地球化学记录的古气候环境演变

Paleoclimatic and Paleoenvironmental Changes Recorded by Elemental Geochemistry in the Northwestern South China Sea since the Past ~55 ka

南海西北部的西沙碳酸盐台地北坡受到陆源和海洋自生物质的供应,蕴含丰富的气候变化信息.为探究该区域的古气候环境演变历史,选取长828 cm的SS7岩心,利用AMS14C测年以及有孔虫氧同位素建立该区域的年代学框架,并进行元素地球化学分析.该岩心底部年龄为~55 ka BP,沉积物的元素主要受到陆源碎屑输入、海洋自生作用、氧化还原条件、海洋化学沉积作用等因素的控制.碎屑组分元素比值K/Rb和K/Ti能用于反映源区地表化学风化程度,进而反映源区过去55 ka的东亚夏季风的演化.区域东亚夏季风在约40 ka BP明显减弱,且对Heinrich、新仙女木等北半球快速变冷的事件有明显地响应.过去55 ka的东亚夏季风,不仅受到北半球低纬度夏季日照辐射量的控制,还受到赤道太平洋大气动力(如太平洋沃克环流)的影响.

The north slope of Xisha carbonate platform in the northwestern South China Sea is supplied by land and marine biogenic materials, so the sediments contain abundant information on climate change. In order to explore the evolution history of paleoclimate and environment in this area, the 828 cm-long core SS7 was selected for elemental geochemical analysis in combination with the chronological framework established by the AMS14C and oxygen isotope of forams. The results show that the core age at bottom is ~55 ka BP, and the elements within sediments are mainly controlled by the terrigenous clastic input, marine authigenesis, redox conditions, and marine chemical deposition. The K/Rb and K/Ti can be used to reflect the surface chemical weathering in the source area and the evolution of the East Asian summer monsoon(EASM) over the past55 ka. The regional EASM apparently decreased at about 40 ka BP, and the decreases of K/Rb and K/Ti values responded to the rapidly cooling events in the northern hemisphere, including the Heinrich events and the Younger Drays. The EASM over the past 55 ka is not only controlled by the summer insolation in the low-latitude of the northern hemisphere, but also affected by the atmospheric dynamics in the equatorial Pacific(such as the Walker circulation in the Pacific).