Contrasting north-south pattern in Holocene lacustrine carbon accumulation in China: Summer monsoon dynamics and human disturbance

Some studies suggest that the lacustrine carbon (C) accumulation has gradually increased during the Holocene in the monsoon region of eastern China, primarily due to the intensified human land use. However, other studies argue that the highest C accumulation in China's lakes occurred in the early Holocene, influenced by high summer insolation. The pattern and driving forces behind Holocene lacustrine C accumulation in eastern China remain controversial. In this study, carbon accumulation rate (CAR) records from eleven lakes in northern China and eight lakes in southern China were synthesized to examine variations in CAR between the two regions and to understand the factors driving these variations. The results reveal that CAR in northern China increased between 11 and 6 thousand calendar years before present (cal ka BP), as the strengthening summer monsoon resulted in increased precipitation, promoting the growth of vegetation in the lake's catchments and subsequently increasing terrestrial sediment and C input into lakes. Conversely, CAR in southern China decreased due to reduced precipitation, leading to a decline in sedimentation rate and C inputs in the lakes. After 6 cal ka BP, decreased precipitation and increased human activities in northern China reduced the forest cover, resulting in a decline in C input into lakes without reducing sediment inputs, which consequently led to a decrease in CAR. In southern China, higher precipitation and intensified human activities significantly increased sediment inputs without affecting C inputs, resulting in an increasing trend in CAR. Thus, human activities and the dipole pattern of precipitation created an inverse phase of C accumulation between northern and southern China in lakes throughout the Holocene. The study also highlights the importance of terrestrial C from the catchment in contributing to lacustrine C accumulation on large regional scale, as C in lake sediments was found to be closely associated with forest cover in the catchment.