Aspects of the role of biogeochemical processes in soils in the global carbon cycle

The average global temperature has been slowly rising during recent decades (Jones et al., 2001) and observed expansion of desertification is attributed, in part, to this temperature rise. Governments of many countries are deeply interested in the processes that drive the temperature increase and the rate of increase, for the purpose of being able to predict future conditions. Large investments. are being made in development and application of mathematical models that can be used to predict future temperature increase and to evaluate measures that can arrest the increase. The models account for the interacting exchange processes between the atmosphere, land, oceans and icefields. Uncertainty in the forecasts arises from uncertainty about the processes represented by the models (Weaver and Zwiers, 2000). The carbon dioxide (CO2) in the atmosphere is considered to be an important contributor to the temperature increase because of its ability to trap long wave radiation coming from the Earth's surface. Thus global warming is associated with the increase in CO2 concentration observed during the past century. In this paper we call attention to the importance of biogeochemical processes of soil ecosystems and to the need to incorporate details of the physical and chemical steps in the mathematical forecasting models. The chemical weathering of carbonate-silicate rocks is one of the principal pathways by which CO2 can be taken from the air over long-term, multimillion year timescales. The weathering steps and therefore the rate of carbon removal from the atmosphere depend very much on the rate of plant growth. We introduce three examples of geochemical processes in the space available to us. Geochemical processes influence the global carbon cycle, and thus, climate change. Here we examine the contributions of the geochemical processes which occur in soil ecosystems. It has been observed that the terrestrial ecosystems of the mid-latitude in the Northern Hemisphere take up and store significant amounts of carbon each year. The phenomenon was first reported by Tans et al. (1990) and later confirmed by Ciasis et al. (1995). This observation suggests that the relation between recently observed global warming trends and the increasing cor centration of carbon dioxide in the atmosphere is more complicated than implied by the emphasis on contributions from burning fossil fuels. Evaluation of the distribution of the landmasses on the globe shows that a large fraction of the total land mass is at the mid-latitude of the Northern Hemisphere., Thus, it is logical to look for the hypothesized soil ecosystem sink in the Northern Hemisphere. Identification of the mechanisms that could drive such a sink is important. We suggest that the mechanisms responsible for the sink could be leaching of dissolved inorganic carbon from soils to groundwater which could in turn carry the carbon to rivers and finally to the, oceans where precipitation occurs, and/or processes which extract the carbon from the air as a result of dissolution of carbonate and silicate rocks. Products from this dissolution are also carried to the oceans where carbonates are precipitated. We show examples of current biogeochemical processes in soil ecosystems and note that these processes continue to make a powerful contribution to the global carbon cycle.