Increased radiocarbon age offset of crater lake sediments linked to cool-dry intervals during the past 40,000 yr

Previous studies of the carbon reservoir effect in lake sediments and its influencing factors have focused mainly on the Holocene; however, changes in carbon reservoir effect and its driving mechanisms before the Holocene remain poorly understood. In this study, we produced a time series of changes in the bulk sediment carbon age offset (Delta t) from Wudalianchi Tianchi Lake, northeastern (NE) China. The results showed that changes in Delta t largely corresponded to temperature and precipitation variations during the Last Glacial and Holocene. During relatively warm -humid periods, the low or zero Delta t mainly resulted from increases in vegetation/phytomass which caused the increased relative contribution of contemporaneous carbon to the sedimentary total organic carbon. In contrast, the higher Delta t during the Last Glacial Maximum was related to increases in old carbon from the surrounding catchment and aeolian dust, and thus to increased relative contribution of old carbon to the sedimentary total organic carbon. This climate-Delta t relationship may also have operated during stadials, interstadials and Heinrich events.