Distinct variations and mechanisms for terrestrial OC 14C-ages in the Eastern China marginal sea sediments since the last deglaciation

Abstract

Marginal seas serve as the depocenter and reactor for terrestrial organic carbon (OC) transported by fluvial systems, however, mechanisms controlling the preservations and radiocarbon ages of down-core sedimentary terrestrial OC still remain poorly understood. Here, we employ radiocarbon analyses of both bulk OC and compound-specific terrestrial biomarker (long chain fatty acids) on sediment cores collected from the Eastern China marginal seas with depositional ages spanning the last 14 kyr. In the southern Yellow Sea (core C04), we find persistent high burial efficiency (94 ± 27% on average) of aged terrestrial OC with apparent initial radiocarbon ages (AIRs, i.e., radiocarbon age corrected for natural decay since deposition) of 1521–6115 yr, which showed an increasing trend from the marine transgression stage to the mid-late Holocene. This trend reflected changes of terrestrial OC age transported by the Huanghe (Yellow River), which in turn was caused by deeper soil erosion of older OC from the Chinese Loess Plateau when rainfall was higher during the mid-late Holocene. In contrast, terrestrial OC AIRs in the East China Sea (core F10B) were significantly older than those in the southern Yellow Sea, with an opposite trend of higher values during marine transgression stage compared with the mid-late Holocene. This spatial difference may arise from significant hydrodynamic process aging in the East China Sea, which further elevated terrestrial OC ages during lateral transports. Our results revealed contrasting scenarios of terrestrial OC ages and preservations in the southern Yellow Sea and the East China Sea, underscoring the important roles of hydroclimate and regional hydrodynamic processes in regulating the burial of terrestrial OC in marginal seas.