Vertical profiles, boundary layer budgets, and regional flux estimates forCO2 and its C-13/C-12 ratio and for water vapor above a forest/bog mosaic in central Siberia

On July 15 and 16, 1996, profiles of temperature, water vapor, carbon dioxi de concentration, and its carbon isotopic composition were made within and above the convective boundary layer (CBL), near the village of Zotino in ce ntral Siberia (60 degreesN, 89 degreesE). On both days the CBL grew to a he ight of around 1000 m at midday after which little further growth was obser ved. This was despite high rates of sensible heat flux into the CBL from th e predominantly coniferous vegetation below and was attributable to a high subsidence velocity. For all flights, marked discontinuities across the top of the CBL were observed for water vapor and CO2 concentrations with diffe rences between the CBL and the free troposphere above being as high as 10 m mol mol(-1) and 13 mu mol mol(-1), respectively. Associated with the lower CO2 concentrations within the CBL was an enrichment of the delta C-13 in CO 2 of up to 0.7 parts per thousand. Although for any one flight, fluctuation s in CO2 and delta C-13 within the CBL were small (less than 3 mu mol mol(- 1) and 0.1 parts per thousand); they were well correlated and suggested a p hotosynthetic discrimination, Delta, by the vegetation below of similar to 17 parts per thousand. Estimates of regional Delta based on CBL budgeting t echniques suggested values ranging from 14.8 to 20.4 parts per thousand. CB L budgeting techniques were also used to estimate regional ecosystem carbon fluxes (-3 to -9 mu mol m(-2) s(-1)) and evaporation rates (1-3 mmol m(-2) s(-1)). Agreement with ground-based tower measurements was reasonable, but a bootstrap error analysis suggested that errors associated with the integ ral CBL technique were sometimes unacceptably large, especially for estimat es of regional photosynthetic C-13 discrimination and regional evaporation rates. Conditions under which CBL techniques should result in reasonably ac curate estimations of regional fluxes and isotopic fractionations are evalu ated.