The calculation of ion pair diffusion coefficients: A comment

It is shown that the values of the diffusion coefficient of MgSO₄⁰ ion pairs computed by Harned and Hudson (J. Am. Chem. Soc., 73: 5880, 1951) and Katz and Ben-Yaakov (Mar. Chem., 8: 263, 1980) are too high by a factor of 2. The correct value of the ion pair diffusion coefficient at infinite dilution was obtained from the measured mutual diffusion coefficient after applying corrections for incomplete dissociation, the electrophoretic effect, the viscosity of the solution and the effect of chloride ion pairs (in the ionic media used during measurements of the stoichiometric association constant of MgSO₄⁰ ion pairs). The MgSO₄⁰ diffusion coefficient is calculated to be 0.65 × 10^?5 cm²₈^?1. The result is independent of the concentration up to a value of 0.8 mol dm^?3.Values were also calculated for the diffusion coefficients of the following ion pairs: NaSO₄^? (0.81 × 10^?5), CaCl⁺ (0.78 × 10^?5), BaCl⁺ (0.85 × 10^?5), NaCl⁰ (0.86 × 10^?5), KCl⁰ (1.09 × 10^?5), NH₄Cl⁰ (1.10 × 10^?5) and CaCl⁰ (1.27 × 10^?5). In general, the diffusion coefficients are less than those of the free ions. The results show quantitative agreement with theoretical predictions.     

Numerical modeling of tides in the Gulf of Suez,Egypt

A vertically integrated two‐dimensional (2‐D) and a five‐layer three‐dimensional (3‐D) numerical models were developed to compute the tides in the Gulf of Suez, Egypt. The computational grid used to schematize the Gulf has a horizontal resolution of 3 × 3 km and consists of a lattice of 23 × 100 points in the 2‐D model and five such lattices in the 3‐D model. Both 2‐D and 3‐D simulations clearly revealed the Kelvin wave nature of the tide with partial reflection. The M₂ simulations also showed a strong tidal signature in the southern sector as compared to the northern part. For the 3‐D simulations, the horizontal and vertical eddy viscosity coefficients and the coefficient of bottom friction were respectively set to 3 × 10⁶ cm²/s, 200 cm²/s, and 0.001. The tidal range decreases from the entrance of the Gulf of Suez toward the Bank of Tor where it reaches a small value and then increases again to about 1.5 m at Suez. A difference of six hours exists between the times of high water at the southern and northern ends of the Gulf. Quantitatively the agreement between the observed and computed tide is better in the 2‐D simulation than in the 3‐D simulation. However, the counterclockwise gyres in the top three layers of the 3‐D model (upper 30 m) during slack water following the flood tide do not appear in the 2‐D simulation.     

A 2—D section of 228Ra and 226Ra in the Northeast Pacific

Seawater samples collected in the northeast Pacific from 112° 50′W to 126° 36′W along a latitudinal band (21–25° N) have been analysed for ²²⁸RA and ²²⁶Ra. Both nuclides exhibit their characteristic distributions. In the surface water, the exponential-like decrease of ²²⁸ Ra away from Baja California can be interpreted by horizontal water mixing with eddy diffusion coefficients (K_x) of 1 × 10⁶ cm² s⁻¹ and 5 × 10⁷ cm² S⁻¹ for scale lengths of 200 km and 1000 km, respectively. In the bottom waters, the decrease of ²²⁸Ra away from bottom sediments can be modeled by vertical eddy diffusivities (K_z) of 15–30 cm² s⁻¹ except at one station (24° 16.9′ N, 115° 8.9′ W) where a value of 120 cm² s⁻¹ is obtained. The ²²⁸Ra-derived diffusivities were used to compute the mass balance of ²²⁶Ra using a two-box model. The model results show a mean mixing coefficient of 3.8 cm² s⁻¹ for the thermocline and a mean upwelling velocity of 7.7 m y⁻¹ in the study area, both are about two or three times higher than those generally quoted for the Pacific.     

Modelling the manganese cycling in two stratified fjords

This paper presents a parameterized model for the particulate and dissolved manganese profiles in two stratified fjords. Rates of oxidation and reduction of manganese are of the order of 1.0 × 10⁻¹⁵ mol cm⁻³ s⁻¹. Oxidation of manganese is probably not promoted by an inorganic surface-catalyzed reaction. Cycling of manganese in the redoxcline is extensive (10–100 cycles) and is related to the input of manganese to the fjords. Calibration of the model against sediment-trap-data allow instantaneous eddy diffusion coefficients to be estimated. These are of the order of 0.01 and 1.0 × 10⁻⁴ cm² s⁻¹.     

Diffusion of seawater ions. Part II. The role of activity coefficients and ion pairing

A theoretical evaluation of basic thermodynamic relationships reveals that variation of activity coefficients, ion pairing and electrical interactions must be considered when modelling ionic diffusion in seawater. The contributions of ion-pair formation and change in activity coefficient along the diffusion path were studied experimentally by conducting diffusion experiments in which solutions of KCl, NaCl, MgCl₂, Li₂SO₄, K₂SO₄, Na₂SO₄ and MgSO₄, at an ionic strength of 0.7, were allowed to diffuse into distilled water. The study reveals that the thermodynamic factor, required to correct for changes in the activity coefficient along the diffusion path, is significant for all the salts studied. Agreement between a simple diffusion model, which does not include ion pairing, and observed data was good for completely dissociated salts, but poor for salts which are known to form ion pairs at the concentration levels studied. The diffusion of MgSO₄, 0.425 of which is associated at I = 0.7, was successfully modelled by assuming that the diffusion coefficient of the MgSO₄⁰ ion pair is different from the diffusion coefficient of the dissociated salt. The diffusion coefficient of this ion pair is estimated to be 1.9 × 10⁻⁵ cm² s⁻¹ at 30°C, as compared to 0.49 × 10⁻⁵ cm² s⁻¹ for the dissociated salt. It is suggested that the high mobility of this ion pair could cause magnesium enrichment in pore water of sulfate depleted sediments.     

黄河口及渤海湾海水的密度

用磁力浮沉子法溶液密度测量装置,在15—25℃之间的三个温度下测定了黄河口渤海湾36个站位海水样品(于1989年7月和1990年7月采集)的密度,发现所有实验测定值与根据其盐度和温度由1980年国际海水状态方程的计算值比较,均有明显的正偏差,此正偏差随海水盐度降低而增大。在黄河口渤海湾海水样品全部盐度范围内,已发现其海水密度正偏差与海水[Ca~(2+)]/s,[Mg~(2+)]/s,[SO_4~(2-)]/s之间呈指数曲线相关,而与碱度之间呈S形曲线相关,但在盐度25.72—31.57范围内都可近似看作直线相关。黄河口渤海湾海水的高碱度、高[Ca~(2+)]/s为其特征,这也是其密度正偏差的主要影响因素。本文还给出了计算黄河口及渤海湾海水密度的公式。     

深圳海域弧菌种类组成、数量分布及其与环境因子的关系研究

研究了深圳海域2008年4月、9月的水体弧菌数量、种类组成及其分布,探讨了弧菌总数及各优势类群的数量分布与环境因子间的相关关系。结果表明:弧菌总数分布具有季节性,东部海域春季(4月)的弧菌数量高于秋季(9月)的,其均值分别为1.50×10⁴ ,8.89×10² CFU/cm³;在西部海域秋季的略高于春季的,其均值分别为5.09×10²,2.66×10² CFU/cm³;弧菌数量最高值出现在大亚湾(4.40×10⁴ CFU/cm³)。弧菌的优势类群具有季节性分布特征:春季特有的优势类群有Vibrio gigantis类似种和V. splendidus类似种,秋季特有的优势类群有V. natriegens类似种;V. alginolyticus类似种是两个季节共有的优势类群,其数量春季高于秋季的。弧菌种类、数量与海水温度、盐度及细菌总数、Chl-a等环境因子有一定的相关性,其中盐度为弧菌种类及数量分布的主要影响因子。     

深圳海域弧菌种类组成、数量分布及其与环境因子的关系研究

研究了深圳海域2008年4月、9月的水体弧菌数量、种类组成及其分布,探讨了弧菌总数及各优势类群的数量分布与环境因子间的相关关系。结果表明:弧菌总数分布具有季节性,东部海域春季(4月)的弧菌数量高于秋季(9月)的,其均值分别为1.50×104,8.89×102CFU/cm3;在西部海域秋季的略高于春季的,其均值分别为5.09×102,2.66×102CFU/cm3;弧菌数量最高值出现在大亚湾(4.40×104CFU/cm3)。弧菌的优势类群具有季节性分布特征:春季特有的优势类群有Vibrio gigantis类似种和V.splendidus类似种,秋季特有的优势类群有V.natriegens类似种;V.alginolyticus类似种是两个季节共有的优势类群,其数量春季高于秋季的。弧菌种类、数量与海水温度、盐度及细菌总数、Chl-a等环境因子有一定的相关性,其中盐度为弧菌种类及数量分布的主要影响因子。     

Greenhouse gases generated from the anaerobic biodegradation of natural offshore asphalt seepages in southern California

Significant offshore asphaltic deposits with active seepage occur in the Santa Barbara Channel offshore southern California. The composition and isotopic signatures of gases sampled from the oil and gas seeps reveal that the coexisting oil in the shallow subsurface is anaerobically biodegraded, generating CO₂ with secondary CH₄ production. Biomineralization can result in the consumption of as much as 60% by weight of the original oil, with ¹³C enrichment of CO₂. Analyses of gas emitted from asphaltic accumulations or seeps on the seafloor indicate up to 11% CO₂ with ¹³C enrichment reaching +24.8‰. Methane concentrations range from less than 30% up to 98% with isotopic compositions of –34.9 to –66.1‰. Higher molecular weight hydrocarbon gases are present in strongly varying concentrations reflecting both oil-associated gas and biodegradation; propane is preferentially biodegraded, resulting in an enriched ¹³C isotopic composition as enriched as –19.5‰. Assuming the 132 million barrels of asphaltic residues on the seafloor represent ~40% of the original oil volume and mass, the estimated gas generated is 5.0×10¹⁰ kg (~76×10⁹ m³) CH₄ and/or 1.4×10¹¹ kg CO₂ over the lifetime of seepage needed to produce the volume of these deposits. Geologic relationships and oil weathering inferences suggest the deposits are of early Holocene age or even younger. Assuming an age of ~1,000 years, annual fluxes are on the order of 5.0×10⁷ kg (~76×10⁶ m³) and/or 1.4×10⁸ kg for CH₄ and CO₂, respectively. The daily volumetric emission rate (2.1×10⁵ m³) is comparable to current CH₄ emission from Coal Oil Point seeps (1.5×10⁵ m³/day), and may be a significant source of both CH₄ and CO₂ to the atmosphere provided that the gas can be transported through the water column.     

共培养条件下强壮前沟藻与中肋骨条藻的相互作用

半连续条件下研究了强壮前沟藻与中肋骨条藻不同接种密度下种间的相互作用,按照以下条件:(1)1×10<'4>个/cm<'3>强壮前沟藻与1×10<'4>个/cm<'3>中肋骨条藻;(2)1×10<'4>个/cm<'3>强壮前沟藻与5×10<'4>个/cm<'3>中肋骨条藻;(3)1×10<'4>个/cm<'3>强壮前沟藻...