Modulating mechanisms of marine hydrodynamics on global coastal carbon burial.

Coastal blue-carbon burial is vulnerable to climate change, yet marine hydrodynamic effects remain poorly quantified. Here we estimate hydrodynamic effects on carbon accumulation rate (CAR), by integrating global observations across mangroves, marshes and seagrasses with multiple drivers. Across all ecosystems, hydrodynamics explains 11.8-16.2% of CAR variability, whereas within individual ecosystems it explains 14.5-31.4%, 13.2-13.9% and 14.7-17.7% in mangroves, marshes and seagrasses, respectively. Limited tidal ranges leave low-CAR, inundation-tolerant seagrasses more common, whereas larger tidal ranges support broader intertidal habitats for high-CAR mangroves and marshes. Wave forcing shows contrasting relationships with CAR: positive in mangroves and seagrasses, potentially linked to organic matter inputs, but negative in marshes, likely reflecting lateral export. As sea-level rise accelerates and storms intensify, carbon-release risks may become heterogeneous, with marshes most vulnerable and mangroves and seagrasses more conditional and regionally uncertain. These findings provide a hydrodynamic framework for predicting future carbon dynamics.