Radiocarbonscapes of Sedimentary Organic Carbon in the East Asian Seas

Abstract

Natural abundance radiocarbon (14 C) is an increasingly widely used tool for investigating the organic carbon (OC) cycle in the contemporary ocean. Recent studies have provided extensive information on the 14 C characteristics of organic matter (OM) in sinking particles and sediments in the East Asian Seas including studies from the Bohai Sea, Yellow Sea, East China Sea, South China Sea, Japan Sea, and Japan Trench. 14 C investigations have provided insights into biogeochemical processes controlling the fate of sedimentary OM in these settings. Here, we highlight these insights from oceanic landscapes stretching across deltas, shelves, abyssal oceans, and the hadal zones of the East Asian Seas; share our perspectives on the source-to-sink dynamics of sedimentary OM in the ocean; and outline the challenges that need to be faced to make the most out of interpreting 14 C signals in sedimentary OC.

Contrasting Sensitivity of Weathering Proxies to Quaternary Climate and Sea‐Level Fluctuations on the Southern Slope of the South China Sea

“…Since relatively coarser‐grained and denser sediments are less liable to rapid seaward transport under such hydrodynamic conditions (Gao & Collins, 2014; Y. Zhu & Chang, 2000), hematite would mostly be deposited proximally on the continental shelf (Figure 4a). Similarly, sluggish across‐shelf bedload transport was observed to be accompanied by the selective degradation of organic carbon in coarser grain size fractions and a pronounced 14 C aging of the residual organic matter (Bao & Blattmann, 2020). As such, despite the potential for rapid formation of hematite and/or its enhanced export by rivers under conditions of a strong EASM, the amount of hematite reaching the deep sea would have been limited at these times.…”

Carbon isotopic constraints on the degradation and sequestration of organic matter in river‐influenced marginal sea sediments

“…This old riverine POC was transported to the offshore location along the steep slope, where it was buried and preserved in the sediment. Overall, the Δ 14 C signatures of SOC in the Chinese marginal seas indicate a provenance‐based effect as river‐derived pre‐aged OC was added to recently synthesized marine OC preserved in sediments (Vonk et al 2012; Bao and Blattmann 2020).…”

Atmospheric Particles Are Major Sources of Aged Anthropogenic Organic Carbon in Marginal Seas

“…Over the last 20 years, anthropogenic activities have greatly modified the atmospheric content and deposition by increasing emissions and altering the tropospheric chemistry of gaseous and particulate organic matter (POM). ,,, With the acceleration of industrialization and urbanization, China has become the world’s largest energy consumer, which has led to high total emissions of air pollutants, especially in the northeast region. , Organic aerosols are a major component of atmospheric aerosols, accounting for up to 20–90% of fine aerosols in the lower troposphere. , Atmospheric transport thus provides large amounts of organic carbon (OC) to marginal seas due to the continental outflow and ocean inflow. − Studies have demonstrated that the deposition and preservation of OC in the surface sediments of the Bohai Sea (BS), Yellow Sea (YS), and East China Sea (ECS) are dominated by old carbon that was largely considered to arise from the discharge of the Yangtze and Yellow Rivers, the two largest rivers in China. − However, the influence of atmospheric deposition on the composition and sources of OC in the sediments of marginal seas has not been well characterized, − , especially for the continental outflow into the BS, YS, and ECS, where organic aerosols are affected by both terrestrial and marine sources under the influence of land/sea breezes. , …”