Holocene organic carbon burial in southwest China and potential response to climate variations

The deposition of organic carbon (OC) in terrestrial water bodies serves as an important carbon sink in global carbon cycle, while the responding mechanism of organic carbon accumulation rate (OCAR) to various climate processes is still unclear. Here, we provide a continuous sediment record covering the past 11.1 kyrs retrieved from Beihai Wetland, which is predominantly influenced by the Indian Summer Monsoon (ISM) in southwest China. The temporal variation of OCAR was established and classified into five evolution stages. Subsequently, potential responses of OCAR to climatic and environmental processes were evaluated based on the Spearman's rank correlation analysis between OCAR and individual sedimentary proxies. During the early Holocene, relatively stable and low OCAR was determined owing to the predominant contributions of detrital influx and low terrestrial organic matters. Following the intensification of summer monsoon and corresponding increase in regional precipitation, extremely low OCAR were yielded in the mid-Holocene, resulted from low values of both sedimentary accumulation rate (SAR) and Loss on Ignition (LOI). The abrupt retreat of ISM led to the development of current wetland from a lake-like system, while the extremely low SAR contributed significantly to the identified low OCAR values between 5.2 and 3.0 cal. kyr BP. Afterwards, the wetland developed progressively following further retreat of ISM, that the preservation of a great amount of organic matters contributed significantly to both SAR and LOI, resulting in the highest OCAR levels during the Holocene. In addition, the rapid decline of OCAR during the last 700 years was interpreted in terms of intensified regional human activities. Such increase in OCAR during the late Holocene was broadly reported from the southwest China, proposing potential responses to the large-scale climate changes, namely the variation of ISM.

Automated summary

The deposition of organic carbon (OC) in terrestrial water bodies is an important carbon sink in the global carbon cycle, but the response mechanism of organic carbon accumulation rate (OCAR) to various climate processes is still unclear. In this study, a continuous sediment record from Beihai Wetland in southwest China was analyzed to establish the temporal variation of OCAR and evaluate its potential responses to climatic and environmental processes. The study found that the OCAR was relatively stable and low during the early Holocene due to the predominant contributions of detrital influx and low terrestrial organic matters. However, the intensification of the summer monsoon and increased regional precipitation resulted in extremely low OCAR in the mid-Holocene. The abrupt retreat of the Indian Summer Monsoon (ISM) led to the development of the current wetland from a lake-like system, and the extremely low sedimentary accumulation rate (SAR) contributed significantly to the identified low OCAR values. The wetland progressively developed following further retreat of the ISM, resulting in the highest OCAR levels during the Holocene. However, in the last 700 years, there was a rapid decline in OCAR due to intensified regional human activities. The increase in OCAR during the late Holocene was proposed to be a response to large-scale climate changes, specifically the variation of the ISM.