GAS SEEPAGE FROM A CARBONATE-CEMENTED SANDSTONE REEF ON THE KATTEGAT COAST OF DENMARK

Gas seepage rates were measured over a two year period at an intertidal/shallow subtidal methane-derived carbonate-cemented sandstone reef off north-east Denmark. The positions of some of the gas outlets at the intertidal site changed with time but the overall gas flux of the reef area remained approximately constant, with a mean flow-rate of 59.4 ml h-1 m-2 or over 100 l h-1 for the seepage area. In the shallows the flow-rates of seeps varied with the depth of the overlying water. The methane from the seeps had a radiocarbon age of >39000 years BP and was depleted in heavy isotopes, (deltaC(CH4)-C-13 varied from -68.6 to -75.3 parts per thousand and deltaD from -240 to -249 parts per thousand, suggesting a bacterial origin. The most C-13-depleted methane came from the most active of the seeps tested.