Abrupt cooling of cold seasons at the middle-late Holocene transition revealed by alkenone records from North China

Abstract

In saline lakes, the paleoenvironmental interpretation of long-chain alkenones (LCAs) is difficult due to the inputs of Isochrysidales Group 2i, which are ice-related bloomers. Here, we perform detailed analysis of LCAs and long-chain alkenoates in sediment cores from Lake Daihai in north China. During the late Holocene, alkenone-inferred temperatures and the Group 2i species abundance indicate a long-term warming trend in cold seasons (winter and early spring), possibly driven by regional insolation and by atmospheric CO2 concentrations. Notably, our records indicate cold climate conditions during the period of 4.3–3.0 cal ka BP, possibly linked to the abrupt expansion of Arctic winter sea ice in a given of low insolation and atmospheric CO2 concentration conditions. The abrupt cooling may have led to the collapse of the East Aian Summer Monsoon (EASM) and the deterioration of the ecosystems in northern China during the middle to late Holocene transition, and thus likely accounted for the nearly synchronous Chinese Neolithic cultural collapses.