Public Seminar by Earth, Ocean and Atmospheric Sciences (EOAS) Thrust, Function Hub, HKUST (GZ) - Rapid Changes of Asian River Derived Materials to the Sea

Recent studies indicate that in the past 50 years, the flow of water and sediments from the world's major rivers has changed markedly. Particularly in Asia, sediment discharge from most major rivers has decreased by 80-90% due to increased human activities (such as building dams, overusing water, and sand mining) and climatic changes. Many of these river deltas, including the Yellow, Red, Mekong, Chao Phraya, and Indus, have been experiencing severe subsidence and coastal erosion. Consequently, most of these deltas have transitioned from a constructive, growing mode to a destructive, declining mode; for instance, the Mekong Delta has exhibited an overall negative net land gain since 2005. Our studies further reveal that not only are the deltaic shorelines retreating, but also some deltas' subaqueous portions are undergoing significant erosion, as observed in the Yangtze, Mekong, Chao Phraya, and Indus rivers.

Case studies on the fates of the world's major rivers, such as the Yangtze, Mekong, and Irrawaddy, including the Ebro River, show that most of these sediments have been transported along the continental shelf, extending 300-800 kilometers away from their river mouths and forming distinctive distal depocenters, some up to 60 meters thick.

In contrast, recent studies have shown that rivers at higher latitudes, such as those in Greenland, have experienced exponential increases in sediment discharge, accounting for 8% of the global river sediment fluxes. Our recent survey in one of Greenland's fjords indicates that strong incisions are occurring on the seafloor due to the increased melting discharge.