ATMOSPHERIC METHANE, RECORD FROM A GREENLAND ICE CORE OVER THE LAST 1000 YEAR

The atmospheric methane concentration in ancient times can be reconstr ucted by analysing air entrapped in bubbles of polar ice sheets. We pr esent results from an ice core from Central Greenland (Eurocore) cover ing the last 1000 years. We observe variations of about 70 ppbv around the mean pre-industrial level, which is confirmed at about 700 ppbv o n a global average. According to our data, the beginning of the anthro pogenic methane increase can be set between 1750 and 1800. Changes in the oxidizing capacity of the atmosphere may contribute significantly to the pre-industrial methane concentration variations, but changes in methane emissions probably play a dominant role. Since methane releas e depends on a host of influences it is difficult to specify clearly t he reasons for these emission changes. Methane concentrations correlat e only partially with proxy-data of climatic factors which influence t he wetland release (the main source in pre-industrial times). A good c orrelation between our data and a population record from China suggest s that man may already have influenced the CH4-cycle significantly bef ore industrialisation.