The northeastern Black Sea redox zone: Hydrochemical structure and its temporal variability

Detailed studies of the vertical structure of hydrochemical parameters in the northeastern Black Sea near Gelendzhik are presented and discussed. This work is based on a set of systematic observations carried out in this region during R/V Akvanavt and R/V Ashamba cruises from 1997 to 2005 and also on data from previous studies from 1984 to 1997. The Black Sea region near Gelendzhik is far from the influences of the Bosporus input and Danube River inflow. Therefore, the vertical structure in this region is more stable compared to the western Black Sea and reflects integrated, rather than local, changes of the Black Sea. Seasonal variations in the distribution of chemical parameters at the redox interface are connected to seasonal variations in hydrophysical processes and organic matter production. In winter, maxima of organic phosphorus and urea were absent in the vicinity of the onset of hydrogen sulfide. The concentrations of nitrate were lower in winter than in summer. Winter mixing in the anticyclone eddies led to reduced vertical gradients in the redox layer and to the disappearance of an upper phosphate minimum. Study of the interannual dynamics of oxygen concentrations in the Cold Intermediate Layer and anoxic waters boundary in the density field position revealed climatic-scale changes that may be connected with changes in the North Atlantic Oscillation (NAO) index. © 2006 Elsevier Ltd. All rights reserved

Моделирование деформаций русел, сложенных мёрзлыми породами, при повышении температуры окружающей среды

This paper is devoted to investigation of the influence of river flow and of the temperature rise on the deformation of the coastal slopes composed of permafrost with the inclusion of ice layer. The method of investigation is the laboratory and mathematical modeling. The laboratory experiments have shown that an increase in water and air temperature changes in a laboratory analogue of permafrost causes deformation of the channel even without wave action, i.e. at steady-state flow and non-erosive water flow velocity. The previously developed model of the bed deformation was improved to account for long-term changes of soil structure with increasing temperature. The three-dimensional mathematical model of coastal slopes thermoerosion of the rivers flowing in permafrost regions, and its verification was based on the results of laboratory experiments conducted in the hydraulic tray. Analysis of the results of mathematical and laboratory modeling showed that bed deformation of the rivers flowing in the permafrost zone, significantly different from the deformation of channels composed of soils not susceptible to the influence of the phase transition «water-ice», and can occur even under the non-erosive velocity of the water flow.Работа посвящена исследованию влияния речного потока и повышения температуры воды на деформации береговых склонов, сложенных многолетнемёрзлыми породами с включением пластов льда. Методы исследования – лабораторное и математическое моделирование. Лабораторные эксперименты показали, что при повышении температуры воды и воздуха изменения в структуре лабораторного аналога многолетнемёрзлого грунта вызывают деформации русла даже без волнового воздействия, т.е. при стационарном режиме течения и неразмывающих скоростях водного потока. В связи с этим возникла необходимость усовершенствования разработанной ранее модели деформации русла с целью учёта долгопериодных изменений структуры грунта при повышении температуры воды. В основу трёхмерной математической модели термоэрозии береговых склонов рек, протекающих в районах развития многолетней мерзлоты, и её верификации положены результаты лабораторных экспериментов в гидравлическом лотке. Анализ результатов математического и лабораторного моделирования показал, что русловые деформации рек, протекающих в криолитозоне, значительно отличаются от деформаций русел, сложенных грунтами, не подверженными влиянию фазового перехода «вода–лёд», и могут наблюдаться даже при неразмывающих скоростях водного потока

Simulation of pollutant transport in mobile water-flow channels in permafrost environment

A common problem for the Arctic region is pollution by persistent organic compounds and other substances that have accumulated over the years in these areas. With temperature increasing, these substances can get out of the snow, ice, permafrost in the human environment. With climate warming and permafrost degradation the risk of toxic substances from the burial sites of chemical and radioactive waste increases. The work is devoted to research the pollution propagation in the rivers flowing in the permafrost taking into account the possible deformations of the channels caused by the melting of the permafrost with increasing temperature of the river flow water. We also consider the distribution of pollutants released during erosion of the coastal slopes, caused thermal erosion. Numerical experiments confirmed the quantitative assessment obtained from the field observations of the erosion rate increases with increasing temperature. Study the impact of thermal and mechanical erosion of the distribution of impurities led to the conclusion that as a result of the formation of taliks uniform flow conditions are violated, resulting in a non-stationary distribution of impurities. The increase in the volume of the test section of the river due to the appearance of cavities in the coastal slope leads to an increase in impurity concentration. Analysis of the results of modeling the spread of contamination during thawing sources in the frozen shores, demonstrated the relationship in the process of distribution of impurities from the position of the source and allowed to give a preliminary quantitative assessment

Assessing the role of thermal erosion in channel deformation processes in rivers of permafrost zone

The study is focused on the deformations caused by the impact of water flow in a river channel composed of melt-able permafrost rocks. It is based on the results of laboratory and mathematical simulation. The results of numerical calculations are compared with data of laboratory and field observations. The study shows that a comprehensive and adequate model of river channel deformations should take into account not only ablation, but also other factors, including heat transfer in the soil, sediment transport, and bank slope collapses. Numerical experiments with an improved mathematical model, applied to long time intervals, have shown that the differences between the averaged deformations, calculated by a model of ablation alone, i.e., ignoring bank slope collapses and sediment transport, and a comprehensive model can be considerable. Experiments in a hydraulic flume were good enough to reproduce the effect of delayed collapse, consisting in nonsimultaneous impacts of channel-forming rock melting and a freshet. © 2020 The Authors, published by EDP Sciences

The Influence of Thermal Erosion at River Bed Deformation in Permafrost Areas

The study is focused on the deformations caused by the impact of water flow in a river channel composed of meltable permafrost bed materials. It is based on the results of laboratory and mathematical simulation. The results of numerical calculations are compared with data of laboratory and field observations. The study shows that a comprehensive and adequate model of river channel deformations should take into account not only ablation, but also other factors, including heat transfer in the soil, sediment transport, and bank slope collapses. Experiments in a hydraulic flume were good enough to reproduce the effect of delayed collapse, consisting in nonsimultaneous impacts of channel-forming rock melting and a freshet. The major factors that have an effect on channel transformations in permafrost-zone rivers are identified. © 2021 American Society of Civil Engineers

Modeling of river bed deformation composed of frozen sediments with increasing environmental temperature

This paper is devoted to investigation of the influence of river flow and of the temperature rise on the deformation of the coastal slopes composed of permafrost with the inclusion of ice layer. The method of investigation is the laboratory and mathematical modeling. The laboratory experiments have shown that an increase in water and air temperature changes in a laboratory analogue of permafrost causes deformation of the channel even without wave action, i.e. at steady-state flow and non-erosive water flow velocity. The previously developed model of the bed deformation was improved to account for long-term changes of soil structure with increasing temperature. The three-dimensional mathematical model of coastal slopes thermoerosion of the rivers flowing in permafrost regions, and its verification was based on the results of laboratory experiments conducted in the hydraulic tray. Analysis of the results of mathematical and laboratory modeling showed that bed deformation of the rivers flowing in the permafrost zone, significantly different from the deformation of channels composed of soils not susceptible to the influence of the phase transition «water-ice», and can occur even under the non-erosive velocity of the water flow

INFLUENCE OF RAINFALL PRECIPITATION ON THE DEFORMATION OF THE RIVER BANK CHANNELS IN PERMAFROST

We studied in the lab the interaction of river runoff from frozen soil, simulating the upper, active-layer, changing the thermal (warming) and mechanical (impact of rain) external influences. We determined the time of thawing of ground and infiltration in soil, sediment transport along the lines under the influence of slope flows, caused by both natural thawing permafrost and storm flows. A mathematical model for predicting the dynamics of river channels in the permafrost under the influence of external factors is suggested

Моделирование переноса загрязнений потоками в деформируемых руслах в условиях криолитозоны

A common problem for the Arctic region is pollution by persistent organic compounds and other substances that have accumulated over the years in these areas. With temperature increasing, these substances can get out of the snow, ice, permafrost in the human environment. With climate warming and permafrost degradation the risk of toxic substances from the burial sites of chemical and radioactive waste increases. The work is devoted to research the pollution propagation in the rivers flowing in the permafrost taking into account the possible deformations of the channels caused by the melting of the permafrost with increasing temperature of the river flow water. We also consider the distribution of pollutants released during erosion of the coastal slopes, caused thermal erosion. Numerical experiments confirmed the quantitative assessment obtained from the field observations of the erosion rate increases with increasing temperature. Study the impact of thermal and mechanical erosion of the distribution of impurities led to the conclusion that as a result of the formation of taliks uniform flow conditions are violated, resulting in a non-stationary distribution of impurities. The increase in the volume of the test section of the river due to the appearance of cavities in the coastal slope leads to an increase in impurity concentration. Analysis of the results of modeling the spread of contamination during thawing sources in the frozen shores, demonstrated the relationship in the process of distribution of impurities from the position of the source and allowed to give a preliminary quantitative assessment.Представлена трёхмерная математическая модель распространения загрязнений в реках, протекающих в условиях криолитозоны, с учётом возможных деформаций русел, вызванных таянием слагающих их многолетнемёрзлых пород при повышении температуры воды речного потока. Рассматривается также распространение загрязняющих веществ, освобождаемых при размыве береговых склонов, обусловленном термоэрозией. Математическая модель состоит из четырёх блоков: гидродинамического, термического, деформационного и распространения примеси. Сравниваются результаты численного моделирования с данными натурных наблюдений и лабораторных экспериментов. На основе численных экспериментов сделаны выводы о характере распространения загрязнений при нахождении их источника в тающих ледяных пластинах, расположенных в береговом откосе