Rates of Organic Carbon Burial in a Floodplain Lake of the Lower Yellow River Area During the Late Holocene

The rapid outward and upward growth of the world's large fluvial sedimentary systems during the second half of the Holocene is a remarkable geologic process that may have buried considerable areas of pre-existing riparian wetlands, which in turn would sequester massive carbon. However, the role of floodplain lakes in the global carbon budget has long been neglected. This article demonstrates the potential of organic carbon burial due to floodplain aggradation during the late Holocene by analyzing a sediment core from a buried floodplain lake in the lower Yellow River area. Based on detailed radiocarbon dating, this study inferred that landscape development in the study area has experienced three disparate stages closely related to the displacement of the lower Yellow River channel. The first stage (∼2250–1700 cal yr BP) represents a widespread pedogenic process while the Yellow River discharged to the northern Bohai Sea through a course much farther north from the present-day position. The subsequent stage (∼1700–1000 cal yr BP) broadly corresponds to the calm period of the Yellow River while it discharged to the southern Bohai Sea through a course slightly north from the present-day position. A lacustrine environment prevailed during this period, sequestering organic carbon at a rate of ∼0.58 kg m2yr1. The final stage (∼1000 cal yr BP to present) is marked by the rapid growth of the floodplain due to the frequent rerouting of the lower Yellow River. This analysis suggests that fluvial sedimentary systems should be integrated into the terrestrial carbon budget when accounting for the aberrant rise of the atmospheric CO2in the face of global cooling during the second half of the Holocene.