Impacts of sea level rise and climate change on the sources, preservation and thermal stability of sedimentary organic carbon in the East China Sea inner shelf since the last deglaciation

Abstract

Large river-dominated marginal seas are important hotspots for organic carbon (OC) burial, yet the long-term preservation of OC from diverse sources and with varying reactivities remains poorly understood. Specific surface area (SSA), median grain size (MGS), total OC (TOC) contents and its stable isotopic composition (δ¹³C), lignin phenols, chlorophyll pigments and thermogravimetric properties of sediments from a gravity core collected from the East China Sea (ECS) inner shelf were analyzed. The overarching objective was to evaluate the impacts of sea level rise and climate change on the sources, preservation and thermal stability of SOC in the ECS inner shelf since the last deglaciation. Prior to seawater intrusion (before 13.2 ka BP), bulk parameters such as TOC and MGS varied slightly, with terrestrial OC being the predominant source. With the sea level rise during the Bølling-Allerød (BA), Younger Dryas (YD) and early Holocene periods (13.2–7.5 ka BP), marine OC increased due to enhanced marine primary production. When the modern current system was established (after 7.5 ka BP), the marine OC decreased along with the increase of soil and plant-derived OC, due in part to increased terrestrial inputs from the Changjiang. Notably, the abrupt cold events occurring during the YD and Holocene periods displayed a significantly higher proportion of terrestrial plant-derived OC with low thermal stability and elevated TOC/SSA ratios. In contrast, thermally stable soil-derived OC was effectively preserved during the mid-late Holocene due to the enhanced East Asian winter monsoon (EAWM) and reduced precipitation. These findings highlight the significance of sea level rise and climate change, especially extreme climate events in the sequestration of OC in coastal sediments.