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Towards an Integrated Model of Weathering, Climate, and Biospheric Processes

Laboratoire d’étude des Mécanismes et Transferts en Géologie, Observatoire Midi-Pyrénées, CNRS-Université de Toulouse, Toulouse, France

Marie-Claire Pierret

Centre de Géochimie de la Surface, Université de Strasbourg, Strasbourg, France

Louis M. François

Laboratoire de Physique Atmosphérique et Planétaire, Université de Liège, Liège, Belgium

Correspondence: Contact e-mail: godderis@lmtg.obs-mip.fr

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
Subaerial weathering of the continental rocks is an important component of global biogeochemical cycles. During the dissolution of continental rocks, atmospheric CO₂ is consumed resulting in alkalinity production and its transfer to the ocean via river transport. Atmospheric carbon is also consumed during the dissolution reaction itself, as illustrated by the dissolution equation of plagioclase:

(1)

Plagioclase dissolution produces dissolved species (basic cations, bicarbonate ions, and silica) and clay minerals which can precipitate locally. Dissolution of carbonate minerals also consumes atmospheric carbon, for example:

(2)

Bicarbonate ions generated from either reaction can be transported to the ocean where it is mixed by the oceanic thermohaline circulation. Both reactions (1) and (2) thus remove carbon from the atmosphere and store it into the oceanic dissolved inorganic carbon reservoir at a timescale of the oceanic mixing (around 5000 yrs today). The total amount of atmospheric carbon being removed through this process has been estimated from the inventory of the amount of bicarbonate ions carried by the world major rivers. It reaches today 0.288 gigatons of carbon per year (GtC/yr) (Gaillardet et al. 1999), 0.14 GtC/yr being consumed by silicate weathering (a number updated to 0.163 GtC/yr by Dessert et al. 2003), and 0.148 GtC/yr by carbonate minerals dissolution. These fluxes are comparable to the net exchange fluxes between the ocean and the atmosphere (0.6 GtC/yr, pre-industrial state) and between the atmosphere and the land biosphere (0.4 GtC/yr, pre-industrial state), making continental weathering a potentially important component of the short term anthropogenic global carbon cycle. This importance has been recently stressed in two studies showing that continental weathering is strongly affected by human activities. Indeed, the HCO₃^– discharge of the Mississippi river has increased by about 25% over the last 40 years probably in response to anthropogenic land use change and agricultural . . . [Full Text of this Article]