CO AND CO2 ISOTOPIC COMPOSITION IN SPITSBERGEN DURING THE 1995 ARCTOCCAMPAIGN

A set of concentration and isotope data for CO and CO2 was obtained du ring the 1995 spring ARCTOC campaign in Spitsbergen. CO mixing ratios decline from 170 nmole/mole in mid April to 120 nmole/mole at the end of the 6-week period, indicating clean air conditions. CO stable isoto pe data show unprecedented enrichment in C-13 increasing with time fro m -25.7 parts per thousand to -23.4 parts per thousand versus V-PDB, w hereas delta(18)O decreases from 8.5 parts per thousand to 2.5 parts p er thousand versus V-SMOW, being higher than SH values as expected. Mu ch of the observed changes in the isotope ratios can be explained assu ming an OH sink with the kinetic isotope effect in the sink reaction g overning delta(13)C and delta(18)O seasonality. Non-combustion sources contribute most to the total source strength in Arctic spring, but pa rticularly oxidation of methane is only of minor importance in the NH. (CO)-C-14 values, which decrease from 22 to 16 molecules/cm(3) STP, s how the expected seasonal decline due to increasing destruction by OH. The values are higher than SH data and agree well with the first NH ( CO)-C-14 data obtained by Volt in 1976-78. It is shown that during a t ropospheric low ozone event, a shift in delta(13)C of CO should be ind uced by the reaction CH4 + Cl. This effect is too small to be detected with the present measurements, but it would help to explain small rem aining differences between expected and measured delta(13)C values. CO 2, isotope data reveal an excellent agreement with the NOAA/CMDL scale . With the onset of the growing season mixing ratios slightly decrease towards the end of our sampling period, anticorrelated to delta(13)C( CO2) which increases, while delta(18)O seems to pass its seasonal maxi mum in late May.