20th Century Changes of DOC and Its ¹⁴C Signature Archived in Caucasus Ice-Core: Implications for Past Sources of Organic Carbon Aerosol in South-Eastern Europe

To reconstruct the history of organic carbon (OC) aerosol over south-eastern Europe, dissolved organic carbon (DOC) and its C-14 signature ((DOC)-C-14) were investigated along an ice core drilled at the Mount Elbrus (ELB) in Caucasus. In summer, compared to pre-1945 levels, the DOC concentrations increased by 45% after 1960, the mean (DOC)-C-14 depletion in recent ELB ice relative to atmospheric (CO2)-C-14 of 32% being attributed to fossil-fuel sources. (DOC)-C-14 content of ice deposited during the bomb-peak era (1955-1980) closely followed atmospheric (CO2)-C-14 changes caused by atmospheric nuclear tests, suggesting the living biosphere as the main biogenic source of DOC in summer in this region. ELB data contrast with those previously obtained in summer Alpine (western Europe) ice in which a post-1950 doubling of DOC was observed and attributed to enhanced emissions of organic compounds from vegetation in France. This regional difference is discussed with respect to changes of biogenic organic compound emissions in response to past change of use-land and global warming. ELB data document, for the first time, changes of DOC and (DOC)-C-14 in winter mountain ice showing an increase by 44% of DOC levels associated with a C-14 signature being 47% lower than that of atmospheric (CO2)-C-14 in ELB ice deposited after 1960. The C-14 winter ELB ice record followed atmospheric (CO2)-C-14 changes with a delay of similar to 3 years, suggesting that remaining emissions from the living biosphere, together with a small contribution from wood burning, are the main biogenic sources of DOC in winter in this region.