Continental Erosion and Co2 Uptake. Inferences from the Himalayan System

Abstract

Continental erosion via silicate weathering or organic carbon erosion/burial is considered has a first order control on long term changes in the level of CO2 in the atmosphere and thereby on climatic changes. While the basic concepts of these processes are wellknown, the effectiveness of the different reactions involved remains underconstrained, and recording their importance in the past or even on the modern system is difficult. The controls on erosion and weathering are tightly linked to climatic conditions such as temperature and precipitation leading to complex feedbacks (Walker et al., 1981; Berner, 1995). Tectonic processes may also be important as orogenic belts are preferential places for erosion. At the global scale, attempts have been made to use the marine limestone record of Sr or C isotopic composition to decipher the fluxes of silicate weathering or organic carbon burial in the past. During the Cenozoic, the global cooling of climate roughly parallels the rise in seawater Sr isotopic ratio, leading to the hypothesis that enhanced silicate weathering increased both consumption of CO2 and the riverine flux of Sr (Raymo and Ruddiman, 1992). By studing Himalayan erosion in both the modern river system and the erosion record in synorogenic sedimentary basins we can examine the role of several processes which affect the CO2 budget, and their relationship with seawater tracers. Silicate weathering and C02 uptake. The weathering of silicate rocks on the continental surface consumes atmospheric CO2 to produce alkalinity as schematically represented by the classic 'Urey reactions':