Quantifying the weathered fluxes to the ocean is far from over: the overlooked role of rock coast erosion

GEOTRACES mission is to quantify the sources, transformations and sinks of trace element and their isotopes to the ocean. Source proper quantifications rely on a good appraisal of the annually weathered matter fluxes. Beyond the classical aeolian, glacially-derived and river discharge inputs, the direct rock coast erosion was barely considered so far. Regard and his co-workers (2022, see reference below) warn us about this overlooked vector of matter, revealing that cliff derived sediment supply is only three times less than the solid discharge of rivers (111 ±65 vs. 290 Mt/a) for Europe. Their original study is based on the most-complete cliff retreat rates database available to date. They recommend that this additional sedimentary source must be further investigated for: (i) its signature in the sedimentary records of ocean basins; (ii) its effects on the geochemical ocean budget; and (iii) the consequences of rising sea level on rock coast erosion rates.

Figure 1: Aerial photograph of a cliff in Bidart (Basque Coast, France). Note at the bottom left of the photo, a section of the cliff sliding towards the sea and providing sedimentary input to the ocean (photo “Avion Jaune” for the FEDER-Nouvelle Aquitaine EZPONDA project) © EZPONDA – T. Dewez
Figure 2: Quantitative budget of fluvial, glacial, aeolian and coastal sedimentary sources. Data from existing literature and data from this work (in bold): calculation for Europe and its extrapolation to the global scale. The study reveals that coastal sediment supply (∼46-176 Mt/a range 111 ± 65 Mt/a) is only three times less than the fluvial sediment supply in Europe (290 Mt/a). © V. Regard and M. Prémaillon

Reference:

Regard, V., Prémaillon, M., Dewez, T. J. B., Carretier, S., Jeandel, C., Godderis, Y., Bonnet, S., Schott, J., Pedoja, K., Martinod, J., Viers, J. Fabre, S. (2022). Rock coast erosion: An overlooked source of sediments to the ocean. Europe as an example. Earth and Planetary Science Letters, 579, 117356. Access the paper (free access until 5 March 2022): https://doi.org/10.1016/j.epsl.2021.117356

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