GEOECOLOGICAL INVESTIGATION OF MERCURY ON THE SHELF OF THE NORTH-EASTERN SAKHALIN IN THE PERIOD OF SEISMO-TECTONIC ACTIVATION

Monitoring observations of changes in the levels of methane and mercury concentrations were carried out in the water column of the oil and gas bearing northeastern Sakhalin shelf in the period 1998-2000. Significant differences in the levels of methane and mercury concentrations were revealed on the shallow shelf, on the edge of the shelf, and in the upper part of the continental slope. The maximum concentrations of methane in water (more than 6000 nl/l) were noted over deposits of gas hydrates in the area of methane source discharge at the edge of the shelf. The maximum concentrations of the dissolved form of mercury (up to 0.090 μg/l) were found in the coastal shallow zone of the shelf and above methane sources. The maximum concentrations of suspended mercury (up to 0.036 μg/l) were found within the frontal zone of the East Sakhalin Current. It has been established that the differences in the distribution of methane and mercury concentrations in water are due to the decomposition of gas hydrate deposits during periods of seismotectonic activation of oil and gas bearing structures. Their opening due to stretching contributes to intense emanations of highly toxic dissolved mercury into the shelf waters, leading to environmental disasters on the Sakhalin shelf.