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ASSESSING MODERN RATES OF RIVER SEDIMENT DISCHARGE TO THE OCEAN USING SATELLITE GRAVIMETRY

Abstract : The estimates of the worldwide sediment river discharge to the oceans suffer large uncertainties, mostly because sediment discharge measurements are scarce in space and time. Yet, knowing this sediment budget is critical in Earth and environmental Sciences, since it is under the direct influence of surface processes (such as erosion, transport and sedimentation) and, in particular, controlled by climate, tectonics and human activities (dam, deforestation). Since 2002, the GRACE Satellite provides global gravity time series that have proven useful for quantifying mass transport, including continental water redistribution at the Earth surface (ice sheets and glaciers melting, groundwater storage variations). Because, sediment accumulation in the oceanic sinks leads to a mass increase, we propose to use GRACE data to assess these mass variations, and in turn the sediment discharge to the ocean. However, the order of magnitude of mass variations due to sediments is only one tenth of the magnitude of continental water. As a result, unraveling the sedimentological contribution to GRACE signal is a challenge. To tackle it, we pair the analysis of regularized GRACE solutions at high spatial resolution corrected from all known contributions (hydrology, ocean, atmosphere) to a particle tracking model that predict the location of the sediment sinks for 13 rivers with the highest sediments loads in the world. This particle tracking model combines global reanalysis of oceanic currents with available data on the grain size and the seasonality of the sediments load at the river mouth and is run over the same time range as GRACE data. We find encouraging correlation between GRACE spatial pattern of mass accumulation and the modeled pattern of sedimentation zones for some rivers, although some discrepancies between modeled and observed mass accumulation values are observed. The reasons for these misfits are a combination of inaccuracies both in GRACE solutions and in the particle tracking model: 1) GRACE has a limited spatial resolution and uncertainties, with residual contributions from off-target effects that are poorly estimated; 2) The particle model is highly dependent on the oceanic currents’ velocity field, which also suffers from uncertainties and has limited spatial and temporal resolution as well; 3) We use literature-based estimations of the seasonality of river sediment loads and associated grain sizes, both of which are notoriously uncertain data. We presently aim at refining our sediment particle tracking model in order to get better confidence in the spatial distribution of the sediments. This way, we expect to assess the annual riverine sediment discharge within the uncertainty of GRACE, independently from uncertain in situ rivers’ sediment loads data.
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Conference papers
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https://hal-insu.archives-ouvertes.fr/insu-01406500
Contributor : Isabelle Dubigeon <>
Submitted on : Thursday, December 1, 2016 - 11:37:23 AM
Last modification on : Wednesday, December 4, 2019 - 3:30:04 PM

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  • HAL Id : insu-01406500, version 1

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Maxime Mouyen, Laurent Longuevergne, Philippe Steer, Alain Crave, Cécile Robin. ASSESSING MODERN RATES OF RIVER SEDIMENT DISCHARGE TO THE OCEAN USING SATELLITE GRAVIMETRY. Source to Sink: a long term perspective of sediment budgets and sources characterization, Géosciences-Rennes, Nov 2016, Rennes, France. pp.79. ⟨insu-01406500⟩

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