Modeling the Dynamics of Dissolved Oxygen Concentration in Waters of the Aniva Bay (The Sea of Okhotsk)

Abstract

To determine the risks for mariculture farms, the intra-annual change of dissolved О2 concentration was simulated for five zones in the Aniva Bay using the CNPSi model. Zone 1 differed sharply from other zones as the most shallow and freshened. Zone 2 is characterized by a pronounced water exchange with Zone 3 and Zone 4: during spring two layers were formed and stood out in these zones, in the summer the water column was homogeneous. Zone 3 has free water exchange with the open waters of the La Perouse Strait. An outstanding feature of Zone 4, in the deep-water part of the bay, was a distinctive subsidence of waters in the centre of the anticyclonic circulation and the maximum thermocline depth (up to 60-70 m). Zone 5 extends along the western coast of the Tonino-Aniva Peninsula and is characterized by the constant upwelling of waters during the icefree period, which is clearly expressed by lower water temperatures. The calculation showed that in the areas suitable for mariculture farms coastal waters were provided with oxygen throughout the year. Anaerobic conditions developed in spring only in the deepest parts of the bay. An additional source of oxygen in the Aniva Bay is natural thickets of macrophytes, among which the Japanese saccharin (Saccharina japonica) dominates in terms of biomass and area. Annually, Japanese saccharin itself absorbed at least 1200 tons of C in its biomass and supplied at least 3100 tons of О2. Unlike the artificially grown biomass, the biomass of all macrophytes would remain in the system and be destroyed during the life cycle, and the oxygen would be consumed for oxidation. The carbon accumulated in the biomass would again return to the rapid cycle, with the exception of the amount transported to the deep central part of the bay, where it would slowly decompose under nearly anaerobic conditions. It would be possible to place additional algae plantations in the bay, which could absorb up to 49 500 tons of C annually, while supplying up to 132 000 tons of О2. The obtained model estimates could be a starting point for determining the “baseline” of the content of dissolved oxygen and compiling balance equations for gas flows in the ocean-atmosphere system in the Aniva Bay before the development of seaweed plantations, which simultaneously act as carbon farms.

Assessment of the Hydrochemical Characteristics of the Carbon Observational Site ‘Carbon-Sakhalin’ (Aniva Bay, Sea of Okhotsk)

“…The construction of a liquefied The question of statistical analysis of raw data, especially if they are distributed unevenly in space and time, is always controversial. However, the method chosen here of objective interpolation with a running average proves its consistency in the example of correct results of the combined hydroecological CNPSi model and the oceanographic model of Bergen University [84][85][86].…”

“…It is a better site for sanitary seaweed plantations for wastewater treatment or rapid absorption of CO 2 from the atmosphere [91]. Our calculations show that when growing brown algae Saccharina japonica in Aniva Bay for the purpose of decarbonization, it is possible to additionally sequestrate up to 49.5 thousand tons of C [86]. Successful cultivation of algae, their timely removal from the environment (before the destruction of the thallus) and the production of biochar from them with further industrial use [92][93][94] will increase the absorption of CO 2 from the atmosphere and have a positive impact on the carbon balance of the entire region.…”