Dissolved and particulate forms of iron and manganese in the redox zone of the Black Sea

During the cruises of the R/V Knorr in 2003 and the R/V Akvanavt in 2004–2006, the vertical distribution of the dissolved and particulate forms of iron and manganese in the redox zone was studied in the southwestern and northeastern parts of the Black Sea. The temporal and spatial variations in the distribution of studied elements were shown.     

Variability of the oxygen deficit near the H2S zone in the Black Sea

Historical oceanographic databases are statistically treated to obtain the mean multi-annual oxygen deficit distributions in the 70–90 m layer for the four seasons of the year. Generalization of the results from 1596 measurements has shown that the oxygen deficit is maintained only at one 1°×1° square at a level of 70–90%. This fact is accounted for by the rise of waters in the cyclonic gyre area. Conversely, small oxygen deficit values in the coastal areas are related to the sinking of water, this being consistent with the pattern of vertical circulation in the sea.Translated by V. Puchkin.     

A sulfur budget for the Black Sea anoxic zone

A budget for the sulfur cycle in the Black Sea is proposed which incorporates specific biogeochemical process rates. The average sulfide production in the water column is estimated to be 30–50 Tg yr⁻¹, occurring essentially in the layer between 500 and 2000 m. About 3.2–5.2 Tg sulfide yr⁻¹ form during sulfate reduction in surface sediments of the anoxic zone. Total sulfur burial in anoxic sediments of 1 Tg yr⁻¹ consists of 10–70% (ca. 40–50% is the average) water column formed (syngenetic) component, the rest being diagenetic pyrite. As a maximum, between 3 and 5 Tg yr⁻¹ contribute sulfide to the bottom water or diffuse downward in the sediment. About 20–50 Tg yr⁻¹ sulfide is oxidized mostly at the chemocline and about 10–20% of this amount (4.4–9.2 Tg yr⁻¹) below the chemocline by the oxygen of the Lower Bosphorus Current. A model simulating the vertical distribution of sulfide in the Black Sea water column shows net consumption in the upper layers down to ca. 500 m, essentially due to oxidation at the chemocline, and net production down to the bottom. On the basis of the calculated budget anoxic conditions in the Black Sea are sustained by the balance between sulfide production in the anoxic water column and oxidation at the chemocline. On average the residence time of sulfide in the anoxic zone is about 90–150 yr, comparable to the water exchange time between oxic and anoxic zones. Hydrophysical control on the sulfur cycle appears to be the main factor regulating the extent of anoxic conditions in the Black Sea water column, rather than rates of biogeochemical processes.     

Modeling Black Sea circulation with high resolution in the coastal zone

We present a numerical model of Black Sea circulation based on primitive equations with improved spatial resolution in the coastal zone. The model equations are formulated in a two-pole orthogonal coordinate system with arbitrary locations of the poles and a vertical σ coordinate. Increased horizontal resolution is gained by displacing the pole into the vicinity of the separated subdomain. The problem is solved over a grid with a variable step. The northern coordinate pole is displaced to the vicinity of Gelendzhik; the grid step varies from 150 m in the coastal zone to 4.6 km in the main basin. We simulated the fields of currents, sea level, temperature, and salinity under the given atmospheric forcing in 2007. The model is capable of reproducing the large-scale Black Sea circulation and submesoscale variations in the coastal currents.     

Subsatellite polygon for studying hydrophysical processes in the Black Sea shelf-slope zone

The first data on the creation of the subsatellite polygon on the Black Sea shelf and continental slope in the Gelendzhik area (designed in order to permanently monitor the state of the aquatic environment and biota) and the plans for maintaining and developing this polygon are presented. The autonomous measuring systems of the polygon in the composition of bottom stations with acoustic Doppler current profilers (ADCP), Aqualog robotic profilers, and thermo-chains on moored buoy stations should make it possible to regularly obtain hydrophysical, hydrochemical, and bio-optical data with a high spatial-time resolution and transmit these data to the coastal center on a real-time basis. These field data should be used to study the characteristics and formation mechanisms of the marine environment and biota variability, as well as the water-exchange processes in the shelf-deep basin system, ocean-atmosphere coupling, and many other processes. These data are used to calibrate the satellite measurements and verify the water circulation numerical simulation. It is assumed to use these data in order to warn about the hazardous natural phenomena and control the marine environment state and its variation under the action of anthropogenic and natural factors, including climatic trends. It is planned to use the polygon subsatellite monitoring methods and equipment in other coastal areas, including other Black Sea sectors, in order to create a unified system for monitoring the Black Sea shelf-slope zone.     

Mathematical model for the ecosystem of the Black Sea hydrogen sulphide zone

A model for the ecosystem of the Black Sea hydrogen sulphide zone is suggested which incorporates seven components, namely, the concentrations of hydrogen sulphide, oxygen, dead organic matter, thiosulphates, molecular sulphur, and the biomass of sulphate-reducing and thiobacteria. With the minor terms neglected in the equations governing the system under consideration, the latter was divided into subsystems which allow an approximate calculation of the model components' vertical stationary profiles. The derived components' profiles agree qualitatively with available observations.Translated by V. Puchkin.     

The oxygen minimum zone in the Arabian Sea during 1995

This paper focuses on the characteristics of the oxygen minimum zone (OMZ) as observed in the Arabian Sea over the complete monsoon cycle of 1995. Dissolved oxygen, nitrite, nitrate and density values are used to delineate the OMZ, as well as identify regions where denitrification is observed. The suboxic conditions within the northern Arabian Sea are documented, as well as biological and chemical consequences of this phenomenon. Overall, the conditions found in the suboxic portion of the water column in the Arabian Sea were not greatly different from what has been reported in the literature with respect to oxygen, nitrate and nitrite distributions. Within the main thermocline, portions of the OMZ were found that were suboxic (oxygen less than ∼4.5 μM) and contained secondary nitrite maxima with concentrations that sometimes exceeded 6.0 μM, suggesting active nitrate reduction and denitrification. Although there may have been a reduction in the degree of suboxia during the Southwest monsoon, a dramatic seasonality was not observed, as has been suggested by some previous work. In particular, there was not much evidence for the occurrence of secondary nitrite maxima in waters with oxygen concentrations greater than 4.5 μM. Waters in the northern Arabian Sea appear to accumulate larger nitrate deficits due to longer residence times even though the denitrification rate might be lower, as evident in the reduced nitrite concentrations in the northern part of the basin. Organism distributions showed string relationships to the oxygen profiles, especially in locations where the OMZ was pronounced, but the biological responses to the OMZ varied with type of organism. The regional extent of intermediate nepheloid layers in our data corresponds well with the region of the secondary nitrite maximum. This is a region of denitrification, and the presence and activities of bacteria are assumed to cause the increase in particles. ADCP acoustic backscatter measurements show diel vertical migration of plankton or nekton and movement into the OMZ. Daytime acoustic returns from depth were strong, and the dawn sinking and dusk rise of the fauna were obvious. However, at night the biomass remaining in the suboxic zone was so low that no ADCP signal was detectable at these depths. There are at least two groups of organisms, one that stays in the upper mixed layer and another that makes daily excursions. A subsurface zooplankton peak in the lower OMZ (near the lower 4.5 μM oxycline) was also typically present; these animals occurred day and night and did not vertically migrate.     

Simulation of the impact of internal waves on the oxygen/hydrogen sulphide co-existence zone in the open part of the Black Sea

This paper focuses on the impact of periodic internal waves on the oxygen/hydrogen sulphide co-existence zone in the open Black Sea. The numerical model is based on a set of transport/diffusion equations governing the evolution of oxygen/hydrogen sulphide concentrations and considering the reaction between them. The wave velocity field is determined by solving a spectrum problem for preinertial period internal waves, using the characteristic vertical density profile for summertime. Via analysis of the model data, the influence of wave characteristics on the parameters of the O₂/H₂S co-existence zone has been assessed.Translated by Vladimir A. Puchkin.     

Numerical analysis of the mesoscale features of circulation in the Black Sea coastal zone

The results of simulating the hydrophysical fields of the Black Sea with a resolution of 1.64 × 1.64 km for January–September 2006 with the use of real atmospheric forcing are analyzed. Both vertical turbulent momentum exchange and vertical turbulent heat and salt diffusions are parameterized using the Mellor-Yamada level 2.5 scheme. The results of this numerical experiment are compared with similar data obtained with a horizontal resolution of 5 km. The features of the meso- and submesoscale dynamics of waters in individual sea regions are given. Possible physical mechanisms of forming meso- and submesoscale vortices are studied on the basis of energy analysis. It is shown that, in the absence of significant wind forcing, the main contribution to kinetic energy is made by the buoyancy force and wind-field inhomogeneities result in significant variations in both total vertical viscosity and total vertical diffusion.     

Determination of the reduced sulfur species in the anoxic zone of the Black Sea: A comparison of the spectrophotometry and iodometry techniques

The report presents the results of the studies of the reduced sulfur species in the water of the anoxic zone of the Black Sea. The content of hydrogen sulfide was determined by means of spectrophotometry using dilution with oxygen-free distilled water. The detection limit of the H₂S amounted to 0.3 μM with the method’s precision below 3%. The accuracy of the spectrophotometric determination was verified by iodometry after the fixation of the hydrogen sulfide in zinc acetate under the distillation with argon from the acidified seawater sample.     

A comparison of two methods for determining copper partitioning in oxidized sediments

Model estimations of the proportion of Cu in oxidized sediments associated with extractable organic materials show some agreement with the proportion of Cu extracted from those sediments with ammonium hydroxide. Data were from 17 estuaries of widely differing sediment chemistry. The modelling and extraction methods agreed best where concentrations of organic materials were either in very high concentrations, relative to other sediment components, or in very low concentrations. In the range of component concentrations where the model predicted Cu should be distributed among a variety of components, agreement between the methods was poor. Both approaches indicated that Cu was predominantly partitioned to organic materials in some sediments, and predominantly partitioned to other components (most probably iron oxides and manganese oxides) in other sediments, and that these differences were related to the relative abundances of the specific components in the sediment. Although the results of the two methods of estimating Cu partitioning to organics correlated significantly among 24 stations from the 17 estuaries, the variability in the relationship suggested refinement of parameter values and verification of some important assumptions were essential to the further development of a reasonable model.     

南海北部最小含氧带水下滑翔机观测结果初步分析*

最小含氧带(Oxygen Minimum Zone, OMZ)是指海洋中层水体处存在的稳定的溶解氧(Dissolved Oxygen, DO)极小值层, OMZ的分布与变化对南海生态系统和生地化循环具有重要意义。本文利用2019年7—9月“海翼”号水下滑翔机(Sea-wing Glider)在南海北部陆坡区的组网观测数据, 对南海北部陆坡区OMZ的空间分布特征进行了分析。结果显示, 在垂向上, 研究区域内DO极小值层出现在深度约700~900m处, 其浓度约为80~100μmol·L^-1, 且700~900m深度范围内DO浓度变化不大, 形成了厚度约为200m的OMZ。在水平方向上, OMZ自陆坡西南部起向东北方向延伸, 厚度由西南至东北逐渐变薄, 整体呈楔形分布, 并在靠近吕宋海峡处逐渐消失。此外, 本研究还选取了两台水下滑翔机7—8月连续两周内的观测数据, 经计算显示, OMZ区域内的DO浓度在跨陆坡方向上的平均变化速率为0.023μmol·L^-1·d^-1(增加), 在沿陆坡方向上为-0.034μmol·L^-1·d^-1(减少)。沿吕宋海峡入侵南海的高氧水能够解释OMZ东北部DO浓度局部升高的现象, OMZ的分布特征和形成原因与海水的平流运动、水团分布和水体层化等物理过程, 以及生物呼吸、有机物分解和还原性物质的氧化等多种影响因素有关。     

黄海渔业资源密度空间插值方法的比较研究

空间插值是渔业生态学研究,特别是海洋生态系统模型构建中的常用工具。为找到适合黄海渔业资源密度的插值方法,本文对四种常用的空间插值方法进行了比较研究。四种插值方法分别为反距离加权（Inverse distance weighted,IDW）、全局多项式（global polynomial interpolation,GPI）、局部多项式（local polynomial interpolation,LPI）和普通克里格（ordinary kriging,OK）。采用交叉验证分析（cross-validation diagnostic）确定不同插值方法的准确度。同时,结合渔业资源密度空间分布的可视化表达,比较不同插值方法结果的优劣。结果表明,原始的生物学数据具有典型的非正态分布特征,对数转化方法能让其显著地接近或符合正态分布。四个调查阶段中,指数模型在2014年8月和10月为最佳半方差函数,2015年1月和5月数据具有明显的纯块金效应。配对样本T检验表明,预测数据和实测数据之间没有显著差异（P>0.05）。交叉验证结果表明,OK在2014年10月插值效果最好,IDW在剩余的三个航次表现最佳,GPI和LPI表现效果不佳。OK在空间分布的可视化表达方面效果最好,既不像IDW一样有较多的“牛眼”效应,也不像GPI和LPI一样具有过多的平滑效果。然而,纯块金效应的存在有时会影响OK的应用。综上所述,我们推荐操作简单且处理快速的IDW作为黄海渔业资源密度常规的插值方法。     

Variability of currents in the coastal zone of the Black Sea from long-term measurements with a bottom mounted ADCP

The results of long-term measurements (16 months) of the current??s velocity in the Black Sea coastal zone near Golubaya Bukhta (Blue Bay) by a bottom mounted acoustic Doppler current profiler (ADCP) are presented and discussed. It was found that the alongshore component of the current dominates and its absolute value is an order of magnitude larger than the absolute value of the normal to the shore component. The annual average value of the alongshore current??s velocity is close to zero. A well pronounced oscillatory mode of the alongshore current??s velocity is revealed. This mode is characterized by quasi-periodic changes in the direction of the alongshore current. The maximal amplitudes of the unidirectional alongshore current??s velocity are observed with a time scale from several hours to several days.     

Use of a problem-oriented database for statistical analysis of the hydrochemical characteristics of the redox layer of the Black Sea

A problem-oriented database (PODB) was developed for the statistical analysis of the hydrochemical characteristics of the redox layer of the Black Sea. The paper describes the features of the PODB, including the algorithm of interpolation and the location of the levels of the appearance and disappearance of hydrochemical parameters (the so-called onset levels) based on Akima’s spline. The application of the PODB allowed us to obtain a series of biogeochemical estimates, in particular, (1) to reveal the constancy of the vertical gradients of the hydrochemical parameters at selected density levels; (2) to calculate the seasonal variability of the degree of manifestation of the phosphate minimum in the near-shore and open sea areas; and (3) to calculate the interannual variability of the level of the disappearance of the hydrogen sulfide, ammonium, total manganese, and methane, as well as the oxygen content in the cold intermediate layer, and to find out their relations with the climatic variations.     

Long-term variations of the location of the upper boundary of the hydrogen-sulphide zone in the Black Sea

We analyze the dependence of climatic variations of the location of the upper boundary of the hydrogen-sulphide zone in the Black Sea on the variations of the sea level and various types of atmospheric circulation (according to A.A. Girs). It is discovered that the level of correlation between the indicated parameters is high and that the corresponding plots are in good qualitative agreement. The accumulated results enable us to make an assumption that there exists an 80–100-yr cycle of variation of all analyzed parameters and that the long-term variations of the location of the upper boundary of the hydrogen-sulphide zone can be regarded as a manifestation of global climatic variations. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

Evaluation of the level of technogenic pollution in the coastal zone of the Black Sea near Gelendzhik

The content of technogenic pollutants in the coastal zone of the northeastern part of the Black Sea was evaluated. The quantitative evaluation of the level of technogenic load on the waters of Gelendzhik and Golubaya (Rybatskaya) bays was performed. A list of pollutants exceeding MPC standards was compiled.     

A high accuracy method for determining nitrogen, argon and oxygen in seawater

An improved gas chromatographic system was constructed to analyze oceanic dissolved N₂, Ar and O₂ with a higher accuracy and shorter analytical time. To obtain a higher accuracy of N₂, Ar and O₂ measurements, the following was added to the system: (I) an air trapping system; (II) a N₂–CO₂ trapping system after the operation of the air trapping system; (III) an active carbon column system for separating N₂ and CO₂ completely and (IV) the introduction of automatic valves controlling most of the system. Compared to previous studies, the precision of the measurements of N₂, Ar and O₂ concentrations was higher at 0.04%, 0.05% and 0.02%, respectively, and our analytical time was shorter at 600 s. Using the improved analytical technique, concentrations of N₂ (C_N2, 561.69–611.81 μmol/kg) and Ar (C_Ar, 15.126–16.238 μmol/kg), saturation states of N₂ (ΔN₂, − 5.1–0.9%) and Ar (ΔAr, − 7.0 to − 1.1%) from 0 m to 3000 m depth in the western North Pacific were observed during March 2005. Based on these data, we propose a new concept for estimating the amount of bubble injection (B). The total error in calculating B was estimated to be about 20%. We estimated B from 12 to 43 μmol/kg in this region using the observational values of N₂ and Ar. As each water mass had a significantly different value of B even with an error of 20%, it is possible to use it as an index of sea surface state for when each water mass is produced in the sea surface mixed layer. Moreover, based on our values of B, we estimated preformed dissolved oxygen (DO) (C_preDO, 309–332 μmol/kg) and the saturation state of C_preDO (ΔpreDO, − 7.0 to − 1.2%) in this region. Thus, the difference between C_preDO and DO content in the ocean interior may be a more useful index for biogenic organic decomposition in the ocean field compared to Apparent Oxygen Utilization (AOU). Until now, the estimation of oceanic uptake of anthropogenic CO₂ has used AOU as a major parameter. Therefore, it may be necessary to re-evaluate the oceanic uptake of anthropogenic CO₂ based on our new concept of B.