BGD Biogeosciences Discussions BGD 1810-6285 Copernicus GmbH Göttingen, Germany 10.5194/bgd-6-1345-2009 Global spatial distribution of natural riverine silica inputs to the coastal zone Dürr H. H. 1 2 3 Meybeck M. 2 Hartmann J. 4 Laruelle G. G. 5 Roubeix V. 3 6 Department of Physical Geography, Faculty of Geosciences, Utrecht University, The Netherlands UMR 7619 Sisyphe, Université Pierre et Marie Curie (Paris VI), Paris, France ESA (Ecologie des Systèmes Aquatiques), Université Libre de Bruxelles, Belgium Institute for Applied Geosciences, Darmstadt University of Technology, Germany Department of Earth Sciences – Geochemistry, Faculty of Geosciences, Utrecht University, The Netherlands now at: Cemagref Bordeaux, Gazinet-Cestas, France 27 01 2009 6 1 1345 1401 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.biogeosciences-discuss.net/6/1345/2009/bgd-6-1345-2009.html The full text article is available as a PDF file from http://www.biogeosciences-discuss.net/6/1345/2009/bgd-6-1345-2009.pdf

Silica, SiO<sub>2</sub>, in dissolved (DSi) and particulate (PSi) form, is both a major product of continental weathering as well as an essential nutrient in terrestrial and aquatic systems. Here we present estimates of the spatial distribution of riverine silica fluxes under natural conditions, i.e. without human influence, to ~140 segments of the global coastal zone. Focussing on the construction of the DSi budget, natural DSi concentration is multiplied with discharge of rivers for each segment for documented basins and segments. Segments with no documentation available are estimated using clustered information based mainly on considerations of local lithology, climate, and lake retention. We approximate fluxes of particulate silica in various forms (PSi) from fluxes of suspended matter, calculated from existing models. Results have been established for silica fluxes, concentrations and yields for drainage basins of the different continents, oceans basins as well as coastal segment basins. For the continental surfaces actually draining into the oceans (exorheic regions, representing 114.7 M km<sup>2</sup>), 371 M t y<sup>&minus;1</sup> of DSi and 8835 M t y<sup>&minus;1</sup> of PSi are transported, corresponding to a mean concentration of 9.5 mg l<sup>&minus;1</sup> and 226 mg l<sup>&minus;1</sup>, and to a mean yield of 3.3 t km<sup>&minus;2</sup> y<sup>&minus;1</sup> and 77 t km<sup>&minus;2</sup> y<sup>&minus;1</sup>, respectively. DSi yields exceeding 6.6 t km<sup>&minus;2</sup> y<sup>&minus;1</sup>, i.e. &gt;2&times; the global average, represent 17.4% of the global continental ice-free exorheic area but correspond to 56.0% of DSi fluxes. Pacific catchments hold most of the hyper-active areas (&gt;5&times; global average), suggesting a close connection between tectonic activity and DSi fluxes resulting from silicate weathering. The macro-filters of regional and marginal seas intercept 33% and 46% of the total dissolved and particulate silica fluxes.

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