DEGASSING OF THE BLACK SEA BOTTOM: SIGNIFICANCE FOR GEOLOGICAL EXPLORATION, ECOLOGY AND NAVIGATION

Abstract

This paper is devoted to a review of modern ideas about degassing (mainly methane) from the bottom of the Black Sea. The main goal is to describe methane emissions on the sea bottom, to delineate their spatial distribution, and to provide insight into their possible origin as well as their influence on ecosystems and navigation. It is shown that the Black Sea is the largest meromictic basin, waters of which are enriched with methane. As such, the basin holds great promise for new energy sources to supply the Black Sea countries, and most of Europe as well. The amount of methane is several timeslarger than the known gas reservoirs on Earth. Its presence under the sea bottom is evident from outbursts of submarine mud volcanoes that commonly contain ice-like aggregates of gas (largely methane) hydrates as well as many high-intensity gas seeps and gas bogs that release huge quantities of methane. While gas hydrates accumulate methane, submarine mud volcanoes, gas seeps, and gas bogs release it into the water column largely from deep sources,and much less often as a product of biochemical processes in bottom sediments. There is a certain zoning in the distribution of methane emissions; in particular, seepы are located on the periphery of the basin while gas hydrates are distributed within its central part. While gas seeps can be used as indicators for oil exploration, mud volcanoes can indicate the oil and gas deposits under the sea bottom. An interconnection between mud volcanoes and gas hydratescannot be excluded. It appears that methane in the sea water affects biota in a negative way. Eruptions of mud volcanoes are dangerous for navigation and communications or industrial equipment (cables, gas pipes, etc.) on the sea bottom.