Enhanced coastal trapping of sediment explains offshore water clarification in the Anthropocene

Global river sediment flux, a critical component of Earth's material cycles, is undergoing a dramatic reshaping in the Anthropocene. Recent global-scale satellite observations have revealed a developing conundrum: while nearshore waters at many major river deltas are becoming more turbid, vast continental shelf waters are simultaneously experiencing a widespread 'clarification' phenomenon. These seemingly contradictory findings challenge our traditional understanding of global source-to-sink systems. Here, we propose a "sediment spatial redistribution" hypothesis to unify these observations. This perspective represents a paradigm shift, moving the debate from a linear question of whether global sediment flux is simply increasing or decreasing to a more complex, spatial question of how it is being reorganized at the land-ocean interface. We argue that regardless of the net change in total sediment load reaching the coast, a suite of Anthropocene drivers has enhanced the efficiency of nearshore sediment trapping. Sediment is preferentially captured in zones like estuaries and deltas, while transport to the outer continental shelf is diminished. This new perspective not only provides an integrated framework for understanding coastal geomorphic evolution and ecosystem responses but also points to critical directions for future research on the global sediment cycle.