Distribution of dissolved oxygen and causes of maximum concentration in the Bering Sea in July 2010

According to data obtained in the Bering Sea during the 4th Chinese National Arctic Research Expedition, the distribution of dissolved oxygen （DO） was studied, causes of its maximum concentration were discussed, and the relationships between DO and other parameters, such as saliniW, temperature, and chlorophyll a were analyzed. The results showed DO concentration ranged from 0.53 to 12.05 mg/L in the Bering Sea basin. The upper waters contained high concentrations and the maximum occurred at the depth range from 20 to 50 m. The DO concentration decreased rapidly when the depth was deeper than 200 m and reached the minimum at the depth range from 500 to 1000 m, and then increased slowly with the depth increasing but still kept at a low level. On the shelf, the DO concentration ranged from 6.53 to 16.63 mg/L with a mean value of 10.75 mg/L, and showed a characteristic of decreasing from north to south. The DO concentration was higher in the area between the Bering Sea and Lawrence Island and was lower in the southeast and southwest of Lawrence Island at the latitude of 62°N. The formation of maximum DO concentration was concerned with phytoplankton photosynthesis and formation of the themocline. To the south of Sta. B07 in the Bering Sea basin, the oxygen produced by photosynthesis permeated to the deeper water and the themocline made it difficult to exchange vertically, and to the north of Sta. B07, the maximum DO concen- tration occurred above the themocline due to phytoplankton activities. On the shelf, the oxygen produced by phytoplankton photosynthesis gathered at the bottom of the thermocline and formed the DO maximum concentration. In the Bering Sea basin, the DO and salinity showed a weak negative correlation （r=0.40） when the salinity was lower than 33.1, a significant negative correlation （r=-0.92） when the salinity ranged from 33.1 to 33.7, and an irregular reversed parabola （r=0.95） when the salinity was greater than 33.7. Key words： Bering Sea, dissolved oxygen, maximum concentration, stratification, chlorophyll a

Recent progress on nanomaterial-based electrochemical dissolved oxygen sensors

Dissolved oxygen(DO)usually refers to the amount of oxygen dissolved in water.In the environment,medicine,and fermentation industries,the DO level needs to be accurate and capable of online monitoring to guide the precise control of water quality,clinical treatment,and microbial metabolism.Compared with other analytical methods,the electrochemical strategy is superior in its fast response,low cost,high sensitivity,and portable device.However,an electrochemical DO sensor faces a trade-off between sensitivity and long-term stability,which strongly limits its practical applications.To solve this problem,various advanced nanomaterials have been proposed to promote detection performance owing to their excellent electrocatalysis,conductivity,and chemical stability.Therefore,in this review,we focus on the recent progress of advanced nanomaterial-based electrochemical DO sensors.Through the comparison of the working principles on the main analysis techniques toward DO,the advantages of the electrochemical method are discussed.Emphasis is placed on recently developed nanomaterials that exhibit special characteristics,including nanostructures and preparation routes,to benefit DO determination.Specifically,we also introduce some interesting research on the configuration design of the electrode and device,which is rarely introduced.Then,the different requirements of the electrochemical DO sensors in different application fields are included to provide brief guidance on the selection of appropriate nanomaterials.Finally,the main challenges are evaluated to propose future development prospects and detection strategies for nanomaterial-based electrochemical sensors.

A Hybrid Neural Network Model for Marine Dissolved Oxygen Concentrations Time-Series Forecasting Based on Multi-Factor Analysis and a Multi-Model Ensemble

Dissolved oxygen(DO)is an important indicator of aquaculture,and its accurate forecasting can effectively improve the quality of aquatic products.In this paper,a new DO hybrid forecasting model is proposed that includes three stages:multi-factor analysis,adaptive decomposition,and an optimizationbased ensemble.First,considering the complex factors affecting DO,the grey relational(GR)degree method is used to screen out the environmental factors most closely related to DO.The consideration of multiple factors makes model fusion more effective.Second,the series of DO,water temperature,salinity,and oxygen saturation are decomposed adaptively into sub-series by means of the empirical wavelet transform(EWT)method.Then,five benchmark models are utilized to forecast the sub-series of EWT decomposition.The ensemble weights of these five sub-forecasting models are calculated by particle swarm optimization and gravitational search algorithm(PSOGSA).Finally,a multi-factor ensemble model for DO is obtained by weighted allocation.The performance of the proposed model is verified by timeseries data collected by the pacific islands ocean observing system(PacIOOS)from the WQB04 station at Hilo.The evaluation indicators involved in the experiment include the Nash–Sutcliffe efficiency(NSE),Kling–Gupta efficiency(KGE),mean absolute percent error(MAPE),standard deviation of error(SDE),and coefficient of determination(R^(2)).Example analysis demonstrates that:①The proposed model can obtain excellent DO forecasting results;②the proposed model is superior to other comparison models;and③the forecasting model can be used to analyze the trend of DO and enable managers to make better management decisions.

A numerical model study on the spatial and temporal variabilities of dissolved oxygen in Qinzhou Bay of the northern Beibu Gulf

Oxygen facilitates the breakdown of the organic material to provide energy for life.The concentration of dissolved oxygen(DO) in the water must exceed a certain threshold to support the normal metabolism of marine organisms.Located in the northern B eibu Gulf,Qinzhou B ay receives abundant freshwater and nutrients from several rivers which significantly influence the level of the dissolved oxygen.However,the spatial-temporal variations of DO as well as the associated driving mechanisms have been rarely studied through field observations.In this study,a three-dimension al coupled physical-biogeochemical model is used to investigate the spatial and seasonal variations of the DO and the associated driving mechanisms in Qinzhou B ay.The validation against observations indicates that the model can capture the seasonal and inter-annual variability of the DO concentration with the range of 5-10 mg/L.Sensitivity experiments show that the river discharges,winds and tides play crucial roles in the seasonal variability of the DO by changing the vertical mixing and stratification of the water column and the circulation pattern.In winter,the tide and wind forces have strong effects on the DO distribution by enhancing the vertical mixing,especially near the bay mouth.In summer,the river discharges play a dominant role in the DO distribution by inhibiting the vertical water exchange and delivering more nutrients to the Bay,which increases the DO depletion and results in lower DO on the bottom of the estuary salt wedge.These findings can contribute to the preservation and management of the coastal environment in the northern Beibu Gulf.

Inter-annual variations of dissolved oxygen and hypoxia off the northern Changjiang River(Yangtze River) Estuary in summer from 1997 to 2014

Hypoxia off the Changjiang River Estuary has been the subject of much attention,yet systematic observations have been lacking,resulting in a lack of knowledge regarding its long-term change and drivers.By revisiting the repeated surveys of dissolved oxygen(DO) and other relevant hydrographic parameters along the section from the Changjiang River Estuary to the Jeju-do in the summer from 1997 to 2014,rather different trends were revealed for the dual low-DO cores.The nearshore low-DO core,located close to the river mouth and relatively stable,shows that hypoxia has become more severe with the lowest DO descen ding at a rate of -0.07 mg/(L·a) and the thickness of low-DO zone rising at a rate of 0.43 m/a.The offshore core,centered around 40-m isobath but moving back and forth between 123.5°-125°E,shows large fluctuations in the minimum DO concentration,with the thickness of low-DO zone falling at a rate of -1.55 m/a.The probable factors affecting the minimum DO concentration in the two regions also vary.In the nearshore region,the decreasing minimum DO is driven by the increase in both stratification and primary productivity,with the enhanced extension of the Changjiang River Diluted Water(CDW) strengthening stratification.In the offshore region,the fluctuating trend of the minimum DO concentration indicates that both DO loss and DO supplement are distinct.The DO loss is primarily attributed to bottom apparent oxygen utilization caused by the organic matter decay and is also relevant to the advection of low-DO water from the nearshore region.The DO supplement is primarily due to weakened stratification.Our analysis also shows that the minimum DO concentration in the nearshore region was extremely low in 1998,2003,2007 and 2010,related to El Ni?o signal in these summers.

Exploration of the Existence Forms and Patterns of Dissolved Oxygen Molecules in Water

The structure of liquid water is primarily composed of three-dimensional networks of water clusters formed by hydrogen bonds,and dis-solved oxygen is one of the most important indicators for assessing water qual-ity.In this work,distilled water with different concentration of dissolved oxygen were prepared,and a clear negative correlation between the size of water clus-ters and dissolved oxygen concentration was observed.Besides,a phenomenon of rapid absorption and release of oxygen at the water interfaces was unveiled,suggesting that oxygen molecules predominantly exist at the interfaces of water clusters.Oxygen molecules can move rapidly through the interfaces among water clusters,allowing dissolved oxygen to quickly reach a saturation level at certain partial pressure of oxygen and temperature.Further exploration into the mechanism by molecular dynamics simulations of oxygen and water clusters found that oxygen molecules can only exist stably at the interfaces among water clusters.A semi-empirical formula relating the average number of water molecules in a cluster(n)to ^(17)O NMR half-peak width(W)was summarized:n=0.1 W+0.85.These findings provide a foundation for exploring the structure and properties of water.

Distributions of dissolved oxygen and apparent oxygen utilization in the Cosmonaut Sea and Amundsen Sea in austral summer 2022

Dissolved oxygen(DO)and apparent oxygen utilization(AOU)are essential parameters for evaluating the impact of climate change on marine ecosystems.In this study,we utilized data on DO and AOU collected from the Amundsen Sea(western Antarctic)and the Cosmonaut Sea(eastern Antarctic)during the 38th Chinese National Antarctic Research Expedition,along with chlorophyll a(Chl a)data,to analyze the impact of primary production and the spatial distribution and structural features of water masses in these regions.The findings show that the standard deviation range of parallel DO samples is between 0.1 and 3.9μmol·L^(-1),meeting the precision criteria of the survey method.AOU values lower than 0.0μmol·L^(-1) were commonly observed in the surface waters of both regions,with the highest incidence in the polynya of Amundsen Sea,indicating a strong influence of high primary production.The Cosmonaut Sea exhibited the highest AOU values(higher than 160.0μmol·L^(-1))in the 75-500 m layer,while AOU value in the Amundsen Sea did not exceed 160.0μmol·L^(-1),suggesting potential upwelling of Circumpolar Deep Water to 100 m in the Cosmonaut Sea with minimal changes in its properties,whereas significant changes were noted in the properties of upwelling modified Circumpolar Deep Water in the Amundsen Sea.AOU values lower than 125.0μmol·L^(-1)were detected in the near-bottom waters of the Cosmonaut Sea,indicating the presence of Antarctic Bottom Water.

Simulations of dissolved oxygen concentration in CMIP5 Earth system models

The climatologies of dissolved oxygen concentration in the ocean simulated by nine Earth system models(ESMs) from the historical emission driven experiment of CMIP5(Phase 5 of the Climate Model Intercomparison Project) are quantitatively evaluated by comparing the simulated oxygen to the WOA09 observation based on common statistical metrics. At the sea surface, distribution of dissolved oxygen is well simulated by all nine ESMs due to well-simulated sea surface temperature(SST), with both globally-averaged error and root mean square error(RMSE) close to zero, and both correlation coefficients and normalized standard deviation close to 1. However, the model performance differs from each other at the intermediate depth and deep ocean where important water masses exist. At the depth of 500 to 1 000 m where the oxygen minimum zones(OMZs) exist, all ESMs show a maximum of globally-averaged error and RMSE, and a minimum of the spatial correlation coefficient. In the ocean interior, the reason for model biases is complicated, and both the meridional overturning circulation(MOC) and the particulate organic carbon flux contribute to the biases of dissolved oxygen distribution. Analysis results show the physical bias contributes more. Simulation bias of important water masses such as North Atlantic Deep Water(NADW), Antarctic Bottom Water(AABW) and North Pacific Intermediate Water(NPIW) indicated by distributions of MOCs greatly affects the distributions of oxygen in north Atlantic, Southern Ocean and north Pacific, respectively.Although the model simulations of oxygen differ greatly from each other in the ocean interior, the multi-model mean shows a better agreement with the observation.

Dissolved oxygen sensor based on sol-gel matrix doped with tris(2,2'-bipyridine)ruthenium dichloride

To establish a immobilization method of oxygen sensitive dye, a dissolved oxygen sensor based on a sol-gel matrix doped with ruthenium complex ([Ru(bpy)3]2+) as the oxygen-sensitive material is reported. The results indicate that the I0 /I100 value of the [Ru(bpy)3]2+-doped in tetraethylorthosilane (TEOS) composite films are estimated to be 10.6, where I0 and I100 correspond to the detected fluorescence intensities in pure nitrogen saturated water and pure oxygen saturated water, respectively. Also, the Stern-Volmer plot shows a very good linearity at low dissolved oxygen concentrations. The response time of the composite films is 5 s upon switching from nitrogen saturated water to oxygen saturated water and 10 s from oxygen saturated water to nitrogen saturated water. The dissolved oxygen sensors based on the ruthenium complex/TEOS composite films exhibit greater sensitivity, stability and faster response time as compared to the existing ones. Furthermore, the thin films possess greatly minimized dye leaching effect.

Prediction Model of Dissolved Oxygen Fuzzy System in Aquaculture Pond Based on Neural Network

A dissolved oxygen fuzzy system predicting model based on neural network was put forward in this study. 106 groups of data were used to confirm the fitness of the predicting model. The first 80 groups of data were acted as training input and the other 26 groups of data were acted as the confirmed data in the system. The result showed that the testing data was approximately the same as the predicted data. So it gave a new way to solve the problem that the status of the water quality couldn＇t be predicted in time and it＇s hard to watching and measuring the factors dynamic.

Taxol Production in Suspension Cultures of Taxus chinensis as Affected by the Combination of Nutrient Feed with Dissolved Oxygen Control

Influence of the combination of nutrient feed with dissolved oxygen control on taxol production in suspension cultures of Taxus chinensis (Pilg.) Rehd. was investigated in bioreactors. Addition of feeding medium with 20 g/L sucrose on day 16 enhanced both the biomass and taxol production in 5-L bioreactors. Further investigation of the fed-batch cultures in a 20-L bioreactor showed that cultivation under a low dissolved oxygen tension (DOT) of 20% for the entire culture resulted in the highest taxol content of 0.98 mg/g DW, while the taxol production was lower than that with 40% and 60% DOT. Moreover, taxol accumulation was remarkably improved by the cultivation of cells initially under DOT of 60% for 20 d followed by changing the DOT to 20% for another 12 d. By combining the use of these two strategies, a maximum taxol content of 18.7 mg/L was obtained in a 20-L bioreactor.

Effects of COD/N ratio and DO concentration on simultaneous nitrification and denitrification in an airlift internal circulation membrane bioreactor

The effects of chemical oxygen demand and nitrogen(COD/N)ratio and dissolved oxygen concentration(DO)on simultaneous nitrification and denitrification(SND)were investigated using an airlift internal circulation membrane bioreactor(AIC-MBR)with synthetic wastewater.The results showed that the COD efficiencies were consistently greater than 90% regardless of changes in the COD/N ratio.At the COD/N ratio of 4.77 and 10.04,the system nitrogen removal efficiency became higher than 70%.However,the nitrogen remova...

Impact of Kuroshio on the dissolved oxygen in the East China Sea region

A marine survey was conducted from 18 May to 13 June 2014 in the East China Sea (ECS) and its adjacent Kuroshio Current to examine the spatial distribution and biogeochemical characteristics of dissolved oxygen (DO) in spring. Waters were sampled at 10?25 m intervals within 100 m depth, and at 25?500 m beyond 100 m. The depth, temperature, salinity, and density (sigma- t ) were measured in situ with a conductivity-temperature-depth (CTD) sensor. DO concentrations were determined on board using traditional Winkler titration method. The results show that in the Kuroshio Current, DO content was the highest in the euphotic layer, then decreased sharply with depth to about 1 000 m, and increased with depth gradually thereafter. While in the ECS continental shelf area, DO content had high values in the coastal surface water and low values in the near-bottom water. In addition, a low-DO zone off the Changjiang (Yangtze) River estuary was found in spring 2014, and it was formed under the combined influence of many factors, including water stratification, high primary productivity in the euphotic layers, high accumulation/ sedimentation of organic matter below the euphotic layers, and mixing/transport of oceanic current waters on the shelf. Most notable among these is the Kuroshio intruded water, an oceanic current water which carried rich dissolved oxygen onto the continental shelf and alleviated the oxygen deficit phenomenon in the ECS, could impact the position, range, and intensity, thus the formation/destruction of the ECS Hypoxia Zone.

The temporal-spatial distribution and changes of dissolved oxygen in the Changjiang Estuary and its adjacent waters for the last 50 a

The Changjiang Estuary and its adjacent waters form one of the most important estuarine and coastal areas in China. Multi source and long-term data are assembled to examine the temporal-spatial distribution features of dissolved oxygen （DO） in the Changjiang Estuary and its adjacent waters for the past SO a. The results show that the DO concentration in the surface of different seasons generally stays stable, while the DO concentration in winter displays a slight increase for the last 50 a. The DO average concentration in winter and spring varies from 7 to 11 rag/L, and in summer and autumn from 6 to 8 mg/L. Hypoxic values first appear in May, and low DO value plume can be observed on the bottom in spring along coastal areas of Zhejiang and Fujian Provinces, China. In summer, the plume advances northward, and the hypoxic intensity of northern transects is much higher than southern transects. Until autumn, hypoxia areas fade away little by little, and completely disappear in winter. Within last 50 a, hypoxia in the Changjiang Estuary and its adjacent waters starts to appear in the 1980s. Since 2000, the degree of hypoxia has increased seriously and the distribution depth has become smaller. It is performed based on a large amount of historical data, and the research results will be of great significance to further study on the dynamic development of hypoxia around the Changjiang Estuary.

A VERTICAL DISTRIBUTION MODEL OF NUTRIENTS AND DISSOLVED OXYGEN IN THE SOUTHERN TAIWAN STRAIT

Sinoe vertical transport of nutrients and dissolved oxygen are quite important in the water col-umn and have drawn serious attention these recent years, a one-dmension numerical model is tried to simulate the vertical distribution of nutrients and dissolved oxygen in June at two research sites in the southemTaiwan Strait. Physical transport parameters are calibrated by temperature simulation, and thenare used to simulate the profiles of NO3, PO4 and dissolved oxygen. The simulation was generally success-ful for both stations. The importance of various factors, such as upwelling tidal current andbiogeochemical activities, which influence the vertical distribution of nutrients and dissolved oxygen, is revealed by analysis of the modeling results. Some important rates, fluxes and ratios are also estimated anddiscussed on the basis of simulation.

Modelling nitrogen and phosphorus cycles and dissolved oxygen in the Zhujiang EstuaryⅠ.Model development

An ecosystem-based water quality model was designed to estimate the biochemical reaction of nutrient and dissolved oxygen in conjunction with a three-dimensional hydrodynamic and sediment model. As both phosphorus and nitrogen successively limit phytoplankton growth in many estuaries, the model simulates both there nutrient cycles each using five variables, namely, dissolved inorganic nutri- ent, detritic organic matter, benthic matter, phytoplankton and zooplankton.

Influence of dissolved oxygen content on oxidative stability of linked polymer solution

The influence of dissolved oxygen content on the oxidative stability of a linked polymer solution (LPS) was studied by micro-filtration, dynamic light scattering and viscosity measurements. The results showed that at the same temperature, the degree of the oxidative degradation of the LPS increased and the rapidity of the oxidative degradation was accelerated with the increase of the dissolved oxygen content. Consequently, the size of linked polymer coils (LPCs) of the LPS became small, and the plugging capability of the LPS decreased. At a fixed content of dissolved oxygen, with increasing degradation temperature, almost the same results were observed, namely, an increased degree of oxidative degradation, accelerated rapidity of the oxidative degradation and decreased plugging capacity, with decreased oxidative stability of LPS. At 90 °C, in the presence of oxygen, LPS lost its plugging capability after having been degraded for a period of time. But at 40 °C, LPS with low dissolved oxygen content could be stable for a long time. The decreased plugging ability of LPS after oxidative degradation is mainly caused by the decreased size and number of the LPCs due to the breaking of hydrolyzed polyacrylamide (HPAM) molecule segments and the structural changing of HPAM molecules.

Influence of Dissolved Oxygen on the Protectiveness and Morphological Characteristics of Calcareous Deposits with Galvanostatic Polarization

The influence of dissolved oxygen on calcareous deposits formed under galvanostatic polarization mode was studied.When the dissolved oxygen concentration was less than 7 mg L^(-1),the cathodic protection potential showed a plateau at the initial polarization,and then quickly shifted negatively.While the dissolved oxygen was more than 9 mg L^(-1),the potential shifted negatively in a linear form.After 168 h of polarization,the final protection potential shifted negatively with the decreasing dissolved oxygen concentration.The deposition progress was monitored by electrochemical impedance spectroscopy,and only one single loop was found in Nyquist diagram,indicating deposits of ineffective protectiveness precipitation under the experimental conditions.The protection factor of deposits increased with the decreasing dissolved oxygen concentration which was detected by linear polarization resistance technique.The cathodic electrochemical reaction could change very shortly from oxygen reduction to hydrogen evolution after cathodic protection under very low dissolved oxygen concentration,such as 1 mg L^(-1),resulting in the hydrogen bubbling from the metallic surface and the decrease of deposits protection factor.Observation by scanning electron microscopy and X-ray diffraction analysis demonstrated that the deposits were mainly of calcite under the experimental conditions,and that dissolved oxygen had no effect on the crystalline types of calcium carbonate.

Effects of Rhizosphere Dissolved Oxygen Content and Nitrogen Form on Root Traits and Nitrogen Accumulation in Rice

Dissolved oxygen and nitrogen form have important effects on rice root growth and nitrogen availability.An indica hybrid rice,Guodao 1,and a conventional japonica rice,Xiushui 09,were cultured in hypoxic nutrient solution with NH4NO3 or(NH4)2SO4 as the nitrogen source for six weeks in pools.A portion of the Guodao 1 seedlings after treatment in the pools for four weeks were transferred to a split-root system at different dissolved oxygen contents and cultured for an additional two weeks.Biomass,root morphological traits and nitrogen accumulation were recorded.Under the low rhizosphere dissolved oxygen content(0-1.0 mg/L),plant biomass was significantly increased under NH4NO3-N supply by about 69% in Guodao 1 and 41% in Xiushui 09 compared with those under NH4+-N alone.Similar results were observed for root number,maximum root length,root dry weight and root activity.Nitrogen accumulations in roots and shoots were increased by 60% and 52% for Guodao 1,and by 41% and 33% for Xiushui 09,respectively,in the NH4NO3-N treatment.In the split-root system,the high rhizosphere dissolved oxygen content(8.0-9.0 mg/L) promoted root growth and development.Root biomass was increased by 21.6%,root number by 27%,maximum root length by 14%,and root volume by 10%.Moreover,nitrogen accumulation in roots was increased by 11% under high rhizosphere oxygen conditions.In conclusion,enhanced dissolved oxygen content and combined ammonium-nitrate nitrogen source have positive effects on root growth and nitrogen accumulation of rice plants.

Preliminary study on the dissolved oxygen distributions and the influential factors in the Daliao River estuary and its adjacent areas

Dissolved oxygen (DO) concentrations were surveyed in the Daliao River Estuary in autumn to investigate the temporal and spatial trends of DO distributions. The results indicate that DO is weakly stratified in the Yingkou section of the Daliao River Estuary, and remains constant vertically in the areas near and out of the entrance. Horizontally, both instantaneous and continuous observations show that the Yingkou section of the Daliao River Estuary is affected by hypoxic conditions; while no conditions of low DO have been observed in the areas near and out of the entrance. DO-salinity correlations exhibit different controlling factors of DO distributions in different sections of the Daliao River Estuary. At the upstream part of the Yingkou section of the Daliao River (A1-A4), oxygen demanding materials and the associated biochemical processes are the main factor controlling the DO distribution, but in the lower part of the Yingkou section and the area near and out of the entrance (A5-A15), tidal advections are more influential for DO distributions.