TERRESTRIAL SEDIMENTATION AND THE CARBON-CYCLE - COUPLING WEATHERING AND EROSION TO CARBON BURIAL

This paper examines the linkages between the carbon cycle and sediment ary processes on land. Available data suggest that sedimentation on la nd can bury vast quantities of organic carbon, roughly 10(15) g C yr(- 1). To evaluate the relative roles of various classes of processes in the burial of carbon on land, terrestrial sedimentation was modeled as a series of 864 scenarios. Each scenario represents a unique choice o f intensities for seven classes of processes and two different global wetland distributions. Comparison was made with presumed preagricultur al conditions. The classes of processes were divided into two major co mponent parts: elastic sedimentation of soil-derived carbon and organi c sedimentation of autochthonous carbon. For elastic sedimentation, ma sses of sediment were considered for burial as reservoir sediment, lak e sediment, and combined colluvium, alluvium and aeolian deposits. Whe n the ensemble of models is examined, the human-induced burial of 0.6- 1.5.10(15) g yr(-1) of carbon on land is entirely plausible. This sink reaches its maximum strength between 30 degrees and 50 degrees N. Pad dy lands stand out as a type of land use that warrants future study, b ut the many faces of rice agriculture limit generalization In an extre me scenario, paddy lands alone could be made to buy about 1.10(15) g C yr(-1). Arguing that terrestrial sedimentation processes could be muc h of the sink for the so called ''missing carbon'' is reasonable. Such a hypothesis, however, requires major redesign of how the carbon cycl e is modeled. Unlike ecosystem processes that are amenable to satellit e monitoring and parallel modeling, many aspects of terrestrial sedime ntation are hidden from space.