Esdeveniments | 22 March 2024 | Friday talks

Fluxes and fates of world major river-derived sediments to the sea: from tropical South Asia to Greenland glacial rivers

Share

Summary

Over the past 7,000 years, most of the world's major river deltas have prograded seaward at an average rate of 20-30 meters per year. However, 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, up to 1.3 gigatons per year, 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.

Brief biography

Dr. Paul Liu, is a coastal geologist specialized in the study of world’s river-delta-ocean systems and full professor at North Carolina State University. Dr. Liu received his Ph.D. from Prof. John Milliman at the College of William and Mary, Virginia Institute of Marine Science in 2001, and afterwards was a postdoc fellow in the Woods Hole Oceanographic Institution (WHOI). In the past 20 years, Dr. Liu has extensively studied more than 12 river-dominated ocean margins, for example, the Bohai Sea, the East China Sea, the South China Sea, the Taiwan Strait, the Okinawa Trough, the Gulf of Tonkin, the Vietnam East Sea, Gulf of Thailand, the Andaman Sea, the Gulf of Martaban, the Indus, and the Nile margins. Most recently, Paul has been working on the glacial-dominated river-delta-fjord systems in Greenland. Dr. Liu’s research interests are the river-delta-ocean interactions, specially fluxes and fates of river-derived sediments and nutrients to the sea and their bio-geochemical implications. He has initiated, led, or co-led numerous international collaborations and is very interested in initiating collaborations with colleagues from ICM-CSIC.