Minimum Oxygen Concentration Research Articles

C121 微小重力環境における固体試料の可燃限界に関するスケールモデリング

The flammability limit of flame spread over a solid material with opposed flow was investigated by scale analysis, and the result was compared with the experimental results by parabolic flight. The sample material was a PMMA sheet whose thickness was 125μm. In the scale analysis, the effect of both radiation loss and finite kinetics were included in the expression of non-dimensional flame spread rate. We derived the following equation for non-dimensional spread rate, η+1/Da_R+1/Da〜1, and assumed that the extinction occurred at η〜0. The developed model reasonably predicted the behavior of the flame spread near minimum limiting oxygen concentration (MLOC), but still underestimated MLOC.

칼슘열환원법(熱還元法)에 의한 타이타늄 스크랩의 탈산(脫酸)

본 연구에서는 칼슘에 의한 타이타늄 스크랩의 탈산에 대하여 조사하였다. 타이타늄 스크랩의 탈산에 미치는 스크랩과 칼슘의 질량비, 반응시간, 반응온도, 입자크기, 그리고 산세조건의 영향에 대하여 검토하였다. 실험은 Ar 분위기의 밀폐된 스테인리스강제 반응기 내에서 30분에서 90분까지 실시하였다. 반응온도 <TEX>$1000^{\circ}C$</TEX>, Ti/Ca의 질량비 2.5인 조건에서 30분 동안의 칼슘 열환원반응에 의해 타이타늄 스크랩의 산소농도는 0.54에서 0.19 wt%로 감소하였다. Ti/Ca의 질량비 2.5에서 30분 동안 <TEX>$1100^{\circ}C$</TEX>에서 탈산한 타이타늄 스크랩의 산소농도는 최저 0.126 wt%를 나타내었다. In this study, deoxidation of Ti scrap using liquid calcium was investigated. Experiments were conducted in a closed stainless steel chamber under Ar atmosphere during 30 to 90 minutes. Oxygen content of Ti scrap was reduced from 0.54 to 0.19 wt% by calciothermic reduction in 30 minutes at <TEX>$1000^{\circ}C$</TEX> and 2.5 Ti/Ca mass ratio. By the calciothermic reduction of Ti scrap for 30 minutes under the reaction temperature of <TEX>$1100^{\circ}C$</TEX> and 2.5 Ti/Ca mass, a minimum oxygen content of about 0.126 wt% in Ti scrap was obtained.

Oxygen solubility in silicon-containing Fe-Co melts

Thermodynamic analysis of the oxygen solutions in silicon-containing Fe-Co melts is performed. The equilibrium constant of silicon deoxidation of iron-cobalt melts, the activity coefficients for infinite dilution, and the interaction parameters for melts differing in composition are determined. The dependences of the oxygen solubility in the melts under study are calculated for different cobalt and silicon contents. The deoxidizing capacity of silicon increases substantially as the cobalt content in a melt increases. The curves of oxygen solubility in Fe-Co melts have a minimum; the minimum oxygen solubility shifts to a low silicon content as the cobalt content in the melts increases. The silicon contents for the minima in the curves of oxygen solubility and the minimum oxygen concentrations corresponding to the silicon contents are determined.

Ventilation effects in confined and mechanically ventilated fires

The main objective of this work is to study underventilated and highly underventilated fires in a compartment equipped with a mechanical ventilation network. Heptane and dodecane pool fire experiments are performed in a reduced-scale room. A changing-scale analysis is performed in order to obtain species concentrations and temperature levels at a larger scale. Carbon dioxide concentration increases linearly with the decreasing of oxygen concentration. Heat release rate depends on ventilation condition in the compartment and we can distinguish three cases. The first one corresponds to sufficiently ventilated fires, where heat release rate is higher or equal to the one of an open fire and where the reaction is almost complete. The second one includes underventilated fires for oxygen concentration ranging between the Minimum Oxygen Concentration of the given fuel and around 7% (this value corresponds to the Minimum Oxygen Concentration of carbon monoxide). At this percentage of oxygen, the Heat Release Rate is lower than the one of an open fire and the carbon monoxide production is proportional to oxygen concentration. The third one corresponds to very underventilated fires for oxygen concentration lower than 7%, and where the fire can stop due to a lack of oxygen. In this case, carbon monoxide concentration increases strongly with the decrease of oxygen concentration.

Radiative constraints on the minimum atomic oxygen concentration in the mesopause region

[1] Atomic oxygen [O] plays a fundamental role in the photochemistry and energy budget of the terrestrial mesopause region (80–100 km). [O] is difficult to measure directly and is typically inferred at night from measurements of hydroxyl [OH] or molecular oxygen [O2] emissions. During the day, measurements of ozone [O3] concentration are used to infer [O]. These inferences carry significant uncertainties [Mlynczak et al., 2013a]. Recently, Mlynczak et al. [2013b] have used energy balance principles to set an upper limit on the annual global mean [O] concentration in the mesopause region. In this paper, we use night measurements of OH emission to set a lower limit on the global annual mean atomic oxygen concentration. These independent, radiatively constrained values of the maximum and minimum atomic oxygen concentration also place constraints on the magnitude of dynamical processes in the annual global mean energy budget of the mesopause region.

Coupled physical/biogeochemical modeling including O&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;-dependent processes in the Eastern Boundary Upwelling Systems: application in the Benguela

Abstract. The Eastern Boundary Upwelling Systems (EBUS) contribute to one fifth of the global catches in the ocean. Often associated with Oxygen Minimum Zones (OMZs), EBUS represent key regions for the oceanic nitrogen (N) cycle. Important bioavailable N loss due to denitrification and anammox processes as well as greenhouse gas emissions (e.g, N2O) occur also in these EBUS. However, their dynamics are currently crudely represented in global models. In the climate change context, improving our capability to properly represent these areas is crucial due to anticipated changes in the winds, productivity, and oxygen content. We developed a biogeochemical model (BioEBUS) taking into account the main processes linked with EBUS and associated OMZs. We implemented this model in a 3-D realistic coupled physical/biogeochemical configuration in the Namibian upwelling system (northern Benguela) using the high-resolution hydrodynamic ROMS model. We present here a validation using in situ and satellite data as well as diagnostic metrics and sensitivity analyses of key parameters and N2O parameterizations. The impact of parameter values on the OMZ off Namibia, on N loss, and on N2O concentrations and emissions is detailed. The model realistically reproduces the vertical distribution and seasonal cycle of observed oxygen, nitrate, and chlorophyll a concentrations, and the rates of microbial processes (e.g, NH4+ and NO2− oxidation, NO3− reduction, and anammox) as well. Based on our sensitivity analyses, biogeochemical parameter values associated with organic matter decomposition, vertical sinking, and nitrification play a key role for the low-oxygen water content, N loss, and N2O concentrations in the OMZ. Moreover, the explicit parameterization of both steps of nitrification, ammonium oxidation to nitrate with nitrite as an explicit intermediate, is necessary to improve the representation of microbial activity linked with the OMZ. The simulated minimum oxygen concentrations are driven by the poleward meridional advection of oxygen-depleted waters offshore of a 300 m isobath and by the biogeochemical activity inshore of this isobath, highlighting a spatial shift of dominant processes maintaining the minimum oxygen concentrations off Namibia. In the OMZ off Namibia, the magnitude of N2O outgassing and of N loss is comparable. Anammox contributes to about 20% of total N loss, an estimate lower than currently assumed (up to 50%) for the global ocean.

A134 限界酸素指数に与える温度の影響(OS-1:火災安全・燃焼(2))

This work is devoted to examine the effect of ambient temperature on limiting oxygen index (LOI), whose concept will be utilized to evaluate the safeness of the material bringing into the space environment, currently based on NASA-STD-6001 (TEST 1). For LOI test (= ISO 4589-2), flame spreads toward the downward, whereas for TEST1, flame spreads toward upward, therefore, the criterion for burning for both tests is not identical. Considering the fact that the upward spread is more preferable than downward spread, limiting oxygen concentration given by LOI test method may always over-predict the limiting oxygen concentration for TEST 1 configuration. To cover this discrepancy, the concept of Temperature Oxygen Index (TOI) based on ISO 4589-34) is newly demonstrated to elucidate the applicability to fulfill the current demand. As increase the field temperature, test material might be easy to burn so that limiting oxygen concentration would decrease even in downward spread test method (namely, LOI test method). It is found that increasing temperature results in linear decrease of LOT (minimum oxygen concentration to burn). More importantly, ABS, PC and PMMA shows almost the same decrease rate of LOI against the temperature increase. Further analyses are underway to explain this observed trend.

칼슘열환원(熱還元)에 의한 ZrO2로부터 지르코늄 분말(粉末) 제조(製造)

본 연구에서는 액상 칼슘에 의한 <TEX>$ZrO_2$</TEX>의 직접환원에 대하여 조사하였다. <TEX>$ZrO_2$</TEX>의 직접환원에 미치는 Ca과 <TEX>$ZrO_2$</TEX>의 몰비, 반응시간, 그리고 반응온도의 영향에 대하여 검토하였다. 실험은 5분에서 60분까지 Ar 분위기의 밀폐된 스테인리스강제의 반응기에서 실시하였다. 반응온도 1223 K, Ca과 <TEX>$ZrO_2$</TEX>의 몰비가 3 이상인 조건에서 대부분의 <TEX>$ZrO_2$</TEX>는 5분만에 Zr으로 환원되었다. 반응온도가 1337 K이고 Ca을 이론적인 양의 2배를 첨가한 경우 금속 Zr 중의 산소농도는 최저 0.66 wt%를 나타내었다. 그리고 Zr 입자의 형상은 반응온도와 반응시간에 큰 영향을 받는 것으로 나타났다. In this study, direct reduction of <TEX>$ZrO_2$</TEX> using liquid calcium was investigated. The influence of molar ratio of Ca and <TEX>$ZrO_2$</TEX>, reaction time and temperature on the reduction behavior of <TEX>$ZrO_2$</TEX> was studied. Experiments were conducted in a closed stainless steel chamber under Ar atmosphere during 5 to 60 minutes. Most of the <TEX>$ZrO_2$</TEX> was reduced to Zr in 5 minutes at 1223 K and 3 Ca/<TEX>$ZrO_2$</TEX> molar ratio. The minimum oxygen content in reduced metal Zr was obtained about 0.66 wt% at 1373 K after 30 minutes and 4 Ca/<TEX>$ZrO_2$</TEX> molar ratio. The morphology of zirconium powder obtained was highly affected by the reaction temperature and reaction time.

Autoxidation and acetylene-accelerated oxidation of NO in a 2-phase system: Implications for the expression of denitrification in ex situ experiments

Nitric oxide (NO) is known to induce denitrification in model organisms, but the quantitative effect of NO and its concentration dependency has not been assessed for denitrification in soils. NO is chemically unstable in the presence of oxygen due to autoxidation, and the oxidation of NO is accelerated by acetylene (C2H2) which is commonly used as an inhibitor of N2O reductase in denitrification studies. As a first step to experimentally explore the role of NO in soil denitrification, we investigated NO oxidation kinetics for a closed “two phase” system (i.e. liquid phase + headspace) typically used for denitrification experiments with soil slurries, both with and without acetylene present. Models were developed to adequately predict autoxidation and acetylene-accelerated oxidation. The minimum oxygen concentration in the headspace ([O2]min, mL L−1) for acetylene-accelerated NO oxidation was found to increase linearly with the NO concentration ([NO], mL L−1); [O2]min = 0.192 + [NO] * 0.1 (r2 = 0.978). The models for NO oxidation were then used to assess NO oxidation rates in denitrification experiments with batches of bacterial cells extracted from soil. The batches were exposed to low initial oxygen concentrations in gas tight serum flasks (with and without C2H2), and monitored for O2, NO, N2O and N2 production while depleting the oxygen and switching to anoxic respiration. Acetylene effectively scavenged NO from the cultures until oxygen concentration reached below ∼0.19 mL L−1, and the estimated rate of acetylene-accelerated NO oxidation was more than sufficient to explain an observed reduction of the N2O production induced by acetylene. When [O2] reached below 0.19 mL L−1, the NO concentrations increased and stabilized at the same level as in the treatments without acetylene, but the rate of denitrification was much lower than without acetylene. The results indicate that the early accumulation of 10–20 nM NO during oxygen depletion has a significant effect on the expression of denitrification in soil communities. This warrants a greater interest in NO as a regulator of denitrification in soils and shows that the acetylene inhibition method may be problematic even for intentionally anoxic incubations, unless precautions are taken to secure initial O2 concentrations below 0.19 mL O2 L−1.

Electro-deposition metallic tungsten coatings in a Na2WO4–WO3 melt on copper based alloy substrate

The tungsten coating was prepared by electro-deposition technique on copper alloy substrate in a Na2WO4–WO3 melt. The coating's surface and cross-section morphologies as well as its impurities were investigated by XPS, SEM and line analysis. Various plating durations were investigated in order to obtain an optimal coating's thickness. The results demonstrated that the electro-deposited coating was compact, voidless, crackless and free from impurities. The tungsten coating's maximum Vickers hardness was measured to be 520HV. The tungsten coating's minimum oxygen content was determined to be 0.018wt%. Its maximum thickness was measured to be 1043.67μm when the duration of electrolysis was set to 100h. The result of this study has demonstrated the feasibility of having thicker tungsten coatings on copper alloy substrates. These electrodeposited tungsten coatings can be potentially implemented as reliable armour for the medium heat flux plasma facing component (PFC).

Investigation of engineering aspects in ethane ODH over highly selective Ni0.85Nb0.15Ox catalyst

A wide range of operating variables is investigated in ethane oxidative dehydrogenation reaction over Ni0.85Nb0.15Ox mixed oxide catalyst. Ethane to oxygen ratio C2H6/O2=2 and feed composition of 10% C2H6/5% O2 were selected as the best trade-off between optimum selectivity and acceptable ethane conversion level. Although suppressing oxygen partial pressure was found to increase ethylene selectivity, a minimum oxygen concentration is required in order to maintain the catalyst in oxidized state. Staged oxygen admission leads to an increase in ethylene selectivity but in expense of ethane conversion, as confirmed by experimental and simulation results. Regarding reactor configuration, preliminary testing under fluid bed conditions proved quite promising. Finally, Ni0.85Nb0.15Ox mixed oxide presented satisfactory stability, as proven both by 100 h on stream stability test and by subjection to a steaming procedure after which the catalytic performance was not deteriorated.

Limiting conditions for flame spread in fire resistant fabrics

Fire resistant (FR) fabrics are used for astronauts, firefighter and racecar driver suits. However, their fire resistant characteristics depend on the environmental conditions and require study. Particularly important is the response of these fabrics to varied environments and radiant heat from a source such as an adjacent fire. In this work, experiments were conducted to study the effect of oxygen concentration, external radiant flux and oxidizer flow velocity on the concurrent flame spread over two FR fabrics: Nomex HT90-40 and a Nomex/Nylon/Cotton fabric blend. Results show that for a given fabric the minimum oxygen concentration for concurrent flame spread depends strongly on the magnitude of the external radiant flux. At increased oxygen concentrations the external radiant flux required for flame spread decreases. Oxidizer flow velocity influences the external radiant flux only when the convective heat flux from the flame has similar values to the external radiant flux. The results of this work provide further understanding of the flammability characteristics of fire resistant fabrics in environments similar to those of future spacecrafts.

Numerical simulation on oxygen transfer in a porous scaffold for animal cell culture

Detailed numerical simulations are performed for oxygen transfer around and within a circular scaffold for animal cell culture. The oxygen concentration distribution, minimum oxygen concentration within the scaffold and its corresponding location, as well as the Sherwood number are presented at different Darcy numbers, Reynolds numbers and Damkohler numbers. It is found that if the Reynolds number is increased from 1 to 30, the Sherwood number increases 1 time for a Darcy number of 5×10−6 while 34 times for a Darcy number of 5×10−4. The location of the minimum oxygen concentration is close to the centre of the scaffold when the Darcy number is smaller than about 5×10−5 or the Reynolds number is smaller than about 1, especially for the Damkohler number larger than O(10). The present study may provide useful guidance on design of the bioreactor with scaffold as well as choosing optimal operating parameters.

Hepatic injury in rats exposed to chronic intermittent hypoxia and the effect of tempol

To investigate the mechanism of liver injury in rats exposed to chronic intermittent hypoxia (CIH) and to investigate the effect of tempol (4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl or 4-hydroxy-TEMPO). A CIH animal model of rats was established to mimic the intermittent hypoxia/re-oxygenation (IH/ROX) of obstructive sleep apnea syndrome in humans. Thirty-two healthy male Wistar rats were randomly assigned to 4 groups: conventional intermittent hypoxia group (CIH group), intermittent hypoxia Tempol treatment group (CIH + T group), intermittent hypoxia normal saline matched group (CIH + NS group), and normoxic control group (NC group), with 8 rats in each group. The frequency of every CIH group was 30 times/h, and the minimum oxygen concentration was 5%. After the experiment, sections of liver were stained with hematoxylin-eosin (HE) and the levels of nuclear factor-kappaB (NF-κB), glutathione peroxidase (GSH-PX) and malondialdehyde (MDA) in rat liver homogenate were measured. Liver histology revealed that the CIH group and the CIH + NS group showed hepatocellular swelling with rarefaction of the cytoplasm, hyperchromatosis and hepatocellular membrane disruption, but the liver histology of the CIH + T group and the NC group was normal. Compared with the NC group, the levels of NF-κB and MDA in the CIH group [(12.4 ± 2.0) ng/g, (101 ± 22) µmol/g] and the CIH + NS group [(12.2 ± 1.9) ng/g, (99 ± 18)µmol/g] were increased (all P < 0.05), but the activities of GSH-PX [(88 ± 17) U/mg, (90 ± 15) U/mg] were decreased (all P < 0.05). Compared with the CIH + NS group and the CIH group, the activity of GSH-PX in the CIH + T group [(181 ± 29) U/mg] was increased (P < 0.05), but the levels of NF-κB [(7.8 ± 1.3) ng/g] and MDA [(59 ± 10) µmol/g] were decreased (all P < 0.05). The levels of GSH-PX and MDA in the CIH + T group were not significantly different compared to the NC group (P were 0.242, 0.177 respectively), but the level of NF-κB in the CIH + T group was higher than that in the NC group (P < 0.05). The levels of NF-κB, GSH-PX, and MDA in the CIH + NS group were not significantly different as compared to those in the CIH group (all P > 0.05). The level of NF-κB was correlated negatively with GSH-PX, but positively with MDA (r = -0.754, 0.689, respectively, all P < 0.01) CIH could cause rat liver injury through oxidative stress and activating the proinflammatory transcription factors of NF-κB. Tempol could prevent CIH-induced liver injury through scavenging ROS by its anti-oxidative effect.

Contrasting biogeochemistry of nitrogen in the Atlantic and Pacific Oxygen Minimum Zones

Abstract. We present new data for the stable isotope ratio of inorganic nitrogen species from the contrasting oxygen minimum zones (OMZs) of the Eastern Tropical North Atlantic, south of Cape Verde, and the Eastern Tropical South Pacific off Peru. Differences in minimum oxygen concentration and corresponding N-cycle processes for the two OMZs are reflected in strongly contrasting δ15N distributions. Pacific surface waters are marked by strongly positive values for δ15N-NO3–) reflecting fractionation associated with subsurface N-loss and partial NO3– utilization. This contrasts with negative values in NO3– depleted surface waters of the Atlantic which are lower than can be explained by N supply via N2 fixation. We suggest the negative values reflect inputs of nitrate, possibly transient, associated with deposition of Saharan dust. Strong signals of N-loss processes in the subsurface Pacific OMZ are evident in the isotope and N2O data, both of which are compatible with a contribution of canonical denitrification to overall N-loss. However the apparent N isotope fractionation factor observed is relatively low (&amp;amp;varepsilon;d=11.4 ‰) suggesting an effect of influence from denitrification in sediments. Identical positive correlation of N2O vs. AOU for waters with oxygen concentrations ([O2] &lt; 5 μmol l−1) in both regions reflect a nitrification source. Sharp decrease in N2O concentrations is observed in the Pacific OMZ due to denitrification under oxygen concentrations O2 &lt; 5 μmol l−1.

Minimum Oxygen Concentration to Extinguish Stack Solid Fuel Fires by Means of Air, Diluted by Carbon Dioxide

Minimum Oxygen Concentration to Extinguish Stack Solid Fuel Fires by Means of Air, Diluted by Carbon Dioxide

Effect of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of intumescent flame retardant ethylene-vinyl acetate copolymer

Ethylene vinyl acetate copolymer (EVA) flame retarded by ammonium polyphosphate (APP) and pentaerythritol (PER) was cross-linked by electron beam irradiation. The effects of vinyl acetate content and electron beam irradiation on the flame retardancy, mechanical and thermal properties of EVA composites were investigated. The volatilized products of EVA/APP/PER composites were characterized by thermogravimetric analysis/infrared spectrometry. As VA content increased, the volatilized products increased in the second decomposition step, but decreased in the third decomposition step. For all samples, the increase of irradiation dose could improve both the gel content and the Limit Oxygen Index (LOI, the minimum oxygen concentration by volume for maintaining the burning of a material) values of irradiated composites. The mechanical and thermal properties of the irradiated EVA composites were also evidently improved at appropriate irradiation dose as compared with those of unirradiated EVA composites, whereas these properties decrease at higher irradiation dose because of the electron beam irradiation-induced oxidative degradation or chain scission.

Thermodynamics of the oxygen solutions in zirconium-containing iron-nickel melts

Thermodynamic analysis of the oxygen solutions in zirconium-containing iron-nickel melts is carried out. The equilibrium deoxidation constants of the melts by zirconium, the activity coefficients at infinite dilution, and the interaction parameters in melts of various compositions are determined. The dependences of the oxygen solubility in the melts on the nickel or zirconium content are calculated. Zirconium is shown to possess a very high deoxidizing capacity in iron-nickel alloys. The zirconium contents at the minima in oxygen solubility curves and the corresponding minimum oxygen concentrations are determined. As the nickel content in a melt increases to ∼45%, the deoxidizing capacity of zirconium decreases and, then, increases. The deoxidizing capacity of zirconium in pure nickel is noticeably higher than that in pure iron.

Integrated survey of elemental stoichiometry (C, N, P) from the western to eastern Mediterranean Sea

Abstract. This paper provides an extensive vertical and longitudinal description of the biogeochemistry along an East-West transect of 3000 km across the Mediterranean Sea during summer 2008 (BOUM cruise). During this period of strong stratification, the distribution of nutrients, particulate and dissolved organic carbon (DOC), nitrogen (DON) and phosphorus (DOP) were examined to produce a detailed spatial and vertically extended description of the elemental stoichiometry of the Mediterranean Sea. Surface waters were depleted in nutrients and the thickness of this depleted layer increased towards the East from about 10 m in the Gulf of Lion to more than 100 m in the Levantine basin, with the phosphacline deepening to a greater extent than that for corresponding nitracline and thermocline depths. We used the minimum oxygen concentration through the water column in combination with 2 fixed concentrations of dissolved oxygen to distinguish an intermediate layer (Mineralization Layer; ML) from surface (Biogenic Layer; BL), and deep layers (DL). Whilst each layer was represented by different water masses, this approach allowed us to propose a schematic box-plot representation of the biogeochemical functioning of the two Mediterranean basins. Despite the increasing oligotrophic nature and the degree of P-depletion along the West to East gradient strong similarities were encountered between eastern and western ecosystems. Within the BL, the C:N:P ratios in all pools largely exceeded the Redfield ratios, but surprisingly, the nitrate vs. phosphate ratios in the ML and DL tended towards the canonical Redfield values in both basins. A change in particulate matter composition has been identified by a C increase relative to N and P along the whole water column in the western basin and between BL and ML in the eastern one. Our data showed a noticeable stability of the DOC:DON ratio (12–13) throughout the Mediterranean Sea. This is in good agreement with a P-limitation of microbial activities but in contradiction of the accepted concept that N is recycled faster than C. The western and eastern basins had similar or close biological functioning. Differences come from variability in the allochtonous nutrient sources in terms of quantity and quality, and to the specific hydrodynamic features of the Mediterranean basins.

The carbonate system of Amur Bay (sea of Japan) under conditions of hypoxia

In the course of the expedition of the Pacific Oceanological Institute in August 2007, extensive hypoxia was found in the near-bottom layer of the Amur Bay water mass. The hypoxia’s formation was immediately reflected in the values and distribution of the carbonate parameters in the near-bottom waters of the bay. The maximum values of the carbon dioxide partial pressure, the dissolved inorganic carbon, and the total alkalinity were associated with the areas of the minimum oxygen content. The microbial destruction of the dead phytoplankton greatly increased the partial pressure of carbon dioxide, which was over 2000 μatm in the hypoxia centers at a depth of about 20 m. At the same time, the carbon dioxide partial pressure in the surface waters of Amur Bay was considerably lower than that in the atmosphere. Hence, the bay’s aquatic area was a sink for the atmospheric CO2 despite its high content in the near-bottom waters. It was shown that the excess alkalinity associated with the hypoxia sites in the near-bottom layer of water was caused by the sulfate reduction proceeding in the upper layer of the sediment.