CONSUMPTION AND PRODUCTION OF CARBON-MONOXIDE IN SOILS - A GLOBAL-MODEL ANALYSIS OF SPATIAL AND SEASONAL-VARIATION

We have developed a simulation model to estimate net seasonal emission of carbon monoxide (CO) from soils world-wide which implies a smaller biogenic sink for CO than previously surmised. Field measurements hav e suggested that soils can play an important regional role in the net terrestrial exchange of carbon monoxide with the atmosphere. Previous global estimates of the net soil sink for atmospheric CO have been mad e by multiplying averages of small chamber measurements for various so il or vegetation classes by estimates of the area covered by each clas s. Simulation models driven by gridded databases can also contribute t o global flux estimates. Such models are useful for evaluation of pote ntial effects of changes in climate and land use, and for identificati on of weaknesses in both data and mechanistic understanding. We applie d a modified version of Fick's first law based on computations for dif fusivity in aggregated media, together with a soil water balance model run on a 1 degrees global grid, to make independent estimates of CO u ptake by soils worldwide. Unlike previous global assessments, we assum e that gross uptake rates are negligible in very dry desert soils (tha t are mostly devoid of microbial activity), in frozen soils, and in we tlands. The model results support a reference case estimate of 16 Tg C O yr(-1) for gross consumption of atmospheric CO in soils worldwide. H owever, owing to uncertainties in the seasonal boundary conditions and the actual soil depth for CO consumption activity, we estimate that t his reference case for gross CO consumption in soils could go as high as 50 Tg CO yr(-1) globally. We also estimated production of CO from d ecaying soil organic matter as a process of chemical oxidation. Our mo del for gross production of CO from surface soils supports a global re ference case flux of 9.4+/-2.5 Tg CO yr(-1). Combination of gross cons umption and production fluxes implies a global net CO uptake flux of a bout 7-40 Tg CO yr(-1) in soils. Model results also support the hypoth esis that temperate dry zones are the primary global sinks for soil CO , whereas tropical wet zones are the primary global sources for soil C O production. Notably, there is an order-of-magnitude difference betwe en our model estimates and previous sink calculations based on extrapo lations of measured fluxes, which suggests the need for more extensive soil CO flux studies, especially in remote regions where biogenic emi ssions could potentially exceed industrial sources of CO. Copyright (C ) 1996 Elsevier Science Ltd.