The influence of geochemical processes in the near-bottom layer on the hydrochemical characteristics of the waters of the Sea of Japan

Abstract

According to the results of the international expedition aboard the R/Vs Roger Revelle and Professor Khromov in the summer 1999, areas with low oxygen contents (below 210 μM/kg) and those with increased contents of dissolved inorganic carbon and phosphates were found that roughly coincided with one another. These areas are located near the bottom on the southwestern slope of the Tsushima Basin in the region of the Korea Strait and on the continental slope in the region of the Tatar Strait in the northern part of the sea at about 46° N. The set of hydrochemical data points to a high geochemical activity in the near-bottom layer of the areas noted. This activity is confirmed by direct observations of the composition of the interstitial water in the sediments collected in the northern part of the sea during the expedition of R/V Akademik M.A. Lavrent’ev in 2003. It was supposed that the main cause of the increased geochemical activity is the runoff of suspended and dissolved matter from the Korea and Tatar straits. In the areas mentioned, the near-bottom waters are characterized by low values of the nitrogen-phosphorus ratio (below 10), which is geochemical proof of the denitrification process occurring under the conditions of high oxygen concentrations characteristic of the Sea of Japan. Based on the value of the annual production in the Sea of Japan, a rate of denitrification equal to 3.4 × 1012 gN/year was calculated. Hence, it is confirmed that the geochemical processes in the near-bottom layer have a direct influence on the spatiotemporal characteristics of the hydrochemical properties of the waters of the Sea of Japan.