Human-induced changes in fluvial regimes for organic carbon supply and burial off the Yellow River Estuary

Estuarine and coastal areas serve as pivotal components in regulating the global carbon cycle. However, the spatial-temporal evolution of organic carbon (OC) burial, particularly under recent anthropogenic influences remains poorly characterized. As one of the most intensively modified fluvial systems worldwide, the Yellow River exerts disproportionate control over OC processing along the land-ocean continuum. Through systematic analysis of sedimentary organic geochemical records off the Yellow River estuary, this study elucidates the heterogeneous linkages between catchment-scale hydrological forcing and OC burial patterns within the coastal margin. Extensive land use changes have fundamentally restructured vegetation dynamics in the Yellow River Basin, thus significantly affecting the composition of nearshore sedimentary OC. An enhanced contribution of fresh woody plant debris-derived OC since the 1970s could be ascribed to the basin-wide soil conservation practices and the "Grain for Green" program. In the 2000s, the presence of herbaceous plants-derived OC could be more related to the herbaceous plant expansion in the river delta. Generally, nearshore OC records exhibit a more rapid response to the short-term fluvial adjustments, such as channel migration and the Water and Sediment Regulation Scheme. In contrast, offshore OC records primarily reflect stepwise trends associated with the long-term and catchment-scale hydrological changes. This study presents a novel framework for understanding the spatial heterogeneity in the sedimentary responses of OC records across a large-river dominated coastal margin influenced by anthropogenic activities. The findings have major implications for the global carbon cycle in the context of human-induced perturbations.