Hydrochemical studies of deep-water basins of the Caspian Sea in August–September 2013 aboard the R/V Nikifor Shurekov

Special features of the hydrochemical conditions variability in the deep water basins of the Caspian Sea

“…2). The hydrogen sulfide concentration in 2013 reached 4.85 mg/L the South Caspian Basin at the depth of 980 m [3]. In the Middle Caspian Basin, at the depth of 780 m, the recorded hydrogen sulfide concentration was 5.45 mg/L, which exceeds the amounts observed in 1933-1934 (then the maximum recorded hydrogen sulfide concentration was 4.39 mg/L [2]).…”

“…In particular, according to data from 1997, the silicon content at the bottom of the Middle Caspian Basin did not exceed 90 µM, but a concentration of 200 µM was already registered by the year of 2006. In addition, it should be noted that the amount of silicon accumulated at the bottom of the Middle Caspian Basin is now significantly higher than the content of silicon in 1934 (130 µM) in the conditions of a much higher sea level [2,3]. Thus, it seems, that today in the Middle Caspian Basin, the accumulation of nutrients probably proceeds more intensely than during the studies of S.V.…”

“…Weak convective mixing exacerbates the hypoxia in the deep waters and the accumulation of hydrogen sulfide in the bottom layer. The lack of oxygen also causes a grad ual decrease in the thickness of the layer of the nitrate maximum concentrations and a reduction of the con tent of nitrates in it, as noted in the 2010-2013 years [3].…”

Comprehensive study of the Caspian Sea system during the second cruise of the research vessel Nikifor Shurekov

“…Water mass submersion with a mean speed of 0.9 cm/s was noted at this level. A stationary south western near bottom along slope contour current [2] has been revealed in the bottom layer (295 m) with a mean velocity of 8.3 cm/s and a maximal one of 44 cm/s. The water transport through the observation point was more than 1000 km from October 25, 2012 to April 17, 2013 (Fig.…”