Glacial-Interglacial Changes in Continental Weathering: Possible Implications for Atmospheric CO₂

Abstract

An eleven-box model of the ocean-atmosphere subsystem of the global carbon cycle is developed to study the potential contribution of continental rock weathering and oceanic sedimentation to variations of atmospheric CO₂ pressure over glacial-interglacial timescales. The model is capable of reproducing the distribution of total dissolved inorganic carbon, total alkalinity, phosphate, δ¹³C, and Δ¹⁴C between the various ocean basins today, as well as the partial pressure of atmospheric CO₂. A simple sedimentation scheme at 20 different depth levels drives carbonate deposition and dissolution as a function of the depths of carbonate and aragonite lysoclines in each ocean basins considered (Atlantic, Antarctic and Indo-Pacific). The coral-reef erosion-deposition cycle is also taken into account. Furthermore, a simple cycle of oceanic strontium isotopes has been added to this model to take advantage of the ⁸⁷Sr/⁸⁶Sr data recently published by Dia et al. (1992) for the last 300,000 years. These data emphasize the importance of weathering of continental silicate rocks at glacial-interglacial timescales. They are used to construct several scenarios of changes of continental weathering over the last glacial cycles. They suggest that the flux of alkalinity delivered to the ocean from continental silicate weathering may have been substantially larger during glacial times than today. We show that such variations of continental weathering may explain at least in part the observed changes of the partial pressure of atmospheric CO₂ between glacial and interglacial periods.