To what extent do spheroidal carbonaceous particles (SCPs) indicate anthropogenic activities in coastal environments?

Spheroidal carbonaceous fly-ash particles (SCPs), established as a proxy indicator of anthropogenic activities mainly through lake studies, while their reliability in coastal environments remains unclear. We investigated SCP occurrence and distribution in a typical medium-sized delta (Hanjiang River Delta) in East Asia, to provide field-measured data and elucidate transport mechanisms. Results indicate a progressive decline in SCP concentrations from nearshore to offshore surface sediments. Prevailing summer winds, emission source distance, limited runoff and hydrodynamic conditions restrict SCP atmospheric and estuarine transport, confining sedimentary records mainly to near-source areas. Sediment core analyses reveal divergent temporal patterns: the nearshore core YD01 exhibits interdecadal variability closely aligned with historical thermal power generation trends, whereas the offshore core YD15 consistently records low SCP concentrations. Compared with research from the Yangtze River Delta (mega-delta), smaller delta exhibits lower SCP output and transport due to reduced electricity generation and river runoff. Thus, SCP spatiotemporal distribution in subaqueous deltas reflects regional changes in anthropogenic activity intensity, declining with reduced activity and greater transport distance. Our findings suggest that differentiated SCP governance strategies should be implemented for deltas of differing scales. This study provides key data and theoretical insights refining the applicability criteria of Anthropocene sediment proxies and elucidating the spatiotemporal evolution of human-driven pollution dynamics in coastal zones.