Eruptions of methane and hydrogen sulphide from shelf sediments off the coast of Namibia


Marine eruptions of toxic gases (methane, hydrogen sulphide) take place every year off the coast of Namibia, with considerable effects on the whole of the ecosystem in this re-gion. The causes of these gas eruptions have to this day not been sufficiently clarified.

The aim of the joint project was to clarify the spreading and origin of the gas and to ex-amine the eruption mechanisms with a view to climatic and oceanographic factors. The findings lead to the assumption of a better estimate of the direct input of toxic gases from the sediment into the water column and the atmosphere. This in turn forms the basis for the calculation of the geological hazard potential, and progress with regard to a risk forecast for the marine ecosystem can be expected. Investigations of the geographi¬cal distribution of gas eruptions, temporal connections between gas eruptions and ocea¬nographic and climatic factors, the influence of oceanic circulation on processes in the water column and the role of sediments as a gas source and gas storage medium were carried out. It was also planned to obtain data for the above-mentioned investigations by means of satellite remote sensing (water colour, temperature data, wind velocities) and the use of stationary measuring stations in the water column (oxygen content, circula¬tion). Furthermore, shallow seismic methods for the determination of the spatial and temporal distribution of gas in the sediments were to be used, from which indications for the targeted sampling of the sediments can be derived.

A further aim was the clarification of the question of the role played by microorganisms in the processes which result in seasonal gas eruptions. For this purpose it was planned to identify the dominant bacteria communities in the water column and the sediment. Particular attention was paid to sulphur bacteria, to which a key position in the produc¬tion of hydrogen sulphide is attributed. With the aid of these investigations, a quantifica¬tion of sulphide production and sulphide flows was to be undertaken. Besides a genetic classification, it was intended to determine the population dynamics of the bacteria community. To determine the effects of marine diamond mining off the Namibian coast on the bacteria population and thus on possible gas eruptions, it was planned to make resuspension attempts with shelf sediments.

GEOTECHNOLOGIEN ist ein geowissenschaftliches Forschungs- und Entwicklungsprogramm und wird vom Bildungsministerium für Bildung und Forschung (BMBF) und der Deutsche Forschungsgemeinschaft (DFG) gefördert.