Abstract : Continental erosion and sediment redistribution are fundamental Earth's processes linking the Solid Earth with the Earth’s fluid envelopes. Erosion is influenced by climate and tectonics and can be impacted by human activities (agriculture, deforestation, sand extraction). Downstream, the supply of sediment shapes deltas and carries organic matter and nutrients to the ocean, which are critical for marine ecosystems and oil and gas reservoirs. However, the rate of global sediment discharge remains largely unknown and its measurement still represents a daunting challenge in Earth sciences which has hardly been tackled by remote sensing. Main difficulties are twofold: (1) the limited amplitude, likely reaching 20 Gt/year at a global scale and (2) the specific spatial patterns, distributed on mountain ranges/lowland and focused in rivers and ocean.
We report the application of GRACE gravity satellite to infer sediment discharge to the ocean of the world’s largest rivers based on the estimate of mass accumulation in oceanic sedimentation zones. We base our analysis on the complementary strengths of a physically-based sediment advection model for the ocean and a new high-resolution GRACE product (~170 km resolution) to recover low-amplitude sediment mass accumulations. We obtain sediment discharges consistent with in situ measurements for the Amazon, Ganges-Brahmaputra, Changjiang, Indus, and Magdalena rivers. Current limitations to study a larger number of rivers and explore extreme events (accuracy at high resolution, length of time series) are expected to be unlocked with GRACE Follow-on missions. This work paves the way towards a better understanding of how natural and anthropic changes influence modern landscape dynamics using space-based observing systems.