Air-saturated Seawater Research Articles

Origin of hydrocarbon and noble gases, carbon dioxide and molecular nitrogen in the Miocene strata of the eastern part of the Polish Carpathian Foredeep: Isotopic and geological approach

Fifteen natural gas samples were collected from the autochthonous Miocene strata between Dębica and Przemyśl towns in the eastern sector of the Polish Carpathian Foredeep. The samples were analysed for the molecular and stable isotope compositions of carbon (δ13C in CH4, C2H6, C3H8, i-C4H10, n-C4H10 and CO2), hydrogen (δ2H in CH4, C2H6 and C3H8), nitrogen (δ15N in N2), and all stable isotopes of noble gases (He, Ne, Ar, Kr and Xe) in order to reveal the origin and migration pathway of these gases. Methane concentrations usually exceeded 90 vol%. Methane was mainly generated by microbial carbon dioxide reduction. The rhythmic and cyclic deposition of clays, muds and sands in the Miocene marine basin facilitated and intensified microbial processes. Microbial ethane can be produced by methanogenic Archaea from acetate via reduction. Ethane partly contains a minor component generated from early mature thermogenic process. Propane and butanes were also generated thermogenically. The hydrocarbon gases in the Miocene horizons IIA and IIIA of the Góra Ropczycka field were generated at higher maturity thermogenic process than the rest of the analysed Miocene gases probably from the Middle Jurassic type III kerogen. They migrated to the Miocene horizons from the underlying Upper Jurassic horizon IV of the same field along a fault. Carbon dioxide of the analysed Miocene gases was mainly generated by primary microbial processes. Moreover, the total carbon constrained in the analysed Miocene gases from 0.1 to 6 wt% contained mantle-derived carbon, and thus carbon dioxide mantle component. Molecular nitrogen was mainly generated during low-temperature thermal transformation of organic matter. It might also involve a relatively insignificant component released from NH4-rich illites of the clayey facies of Miocene strata and an atmospheric component delivered by recharge of air-saturated seawater to the reservoir. Inorganic fluid supply from greater lithospheric depth would not be responsible for the promotion of thermal transformation of organic matter. Molecular nitrogen from Miocene horizons in the Góra Ropczycka field was generated during the thermal transformation of organic matter of higher maturity than the rest of Miocene gases, and migrated from the Upper Jurassic horizon along a fault. Helium is dominated by its radiogenic component, with a minor contribution from the mantle. The almost constant mixing ratios of the two helium components in the natural gases from Miocene horizons of various depths suggest that He migrated from a common inorganic deep-seated source in the lithosphere. The other noble gases are dominated by atmospheric components delivered to the hydrocarbon reservoirs by recharge of air-saturated seawater, with minor nucleogenic 21Ne, radiogenic 40Ar, and sedimentary Kr and Xe contributions. The atmospheric component is isotopically fractionated for Ne, and elementally fractionated with various degrees. The ratios of radiogenic 4He to nucleogenic 21Ne or radiogenic 40Ar are higher than the crustal production ratios, suggesting fractionation during thermal release from their host minerals and/or phase related fractionation during their transport to the gas reservoirs. The striking similarity in noble gas isotopic/elemental ratios of the Góra Ropczycka gas from the Miocene horizon IIIA to the nearby reservoir in Mesozoic strata is consistent with gas migration along a fault system.

Magmatic fluids play a role in the development of active gas chimneys and massive gas hydrates in the Japan Sea

The Earth's marine continental margins hold significant amount of carbon in the form of gas hydrate which can interact dynamically with seawater and the atmosphere and potentially influence global climate. It is generally assumed that degradation of organic matter, through either biogenic or thermogenic processes, is responsible for the majority of the gas hydrate presently found in these deposits. We present stable isotope and noble gas results from gas hydrates in the eastern margin of the Japan Sea and compare them with previously published data regarding gases which are found nearby in deep hydrocarbon wells associated with Early Miocene igneous and sedimentary rocks. Our results show that most of the gases which accumulate in the hydrate can be described as a mixture between a deeply-sourced methane-rich thermogenic/crustal source (TC), a methane-rich admixture of biogenic gases with relatively shallow air-saturated seawater (BASW) and a methane-poor magmatic-mantle source (MM). The presence of hydrate with a mantle 3He/4He signatures indicates that fluids enriched in mantle gases are responsible for the mobilization of thermogenic gas within active Japan Sea chimney structures. The growth of primary hydrate at shallow marine sediment depths is ongoing, as is the cycling of gas to hydrate which is eventually buried and dissociated at the base of the gas hydrate stability zone, leading to large pockmark structures.

Corrosion behavior of Q235 carbon steel in air-saturated seawater containing Thalassospira sp.

Thalassospira sp. is an iron-reducing bacterium isolated from the marine environment. Effects of T. sp. on corrosion behaviors of Q235 carbon steel in air-saturated seawater were studied. Results of electrochemical measurements and weight loss indicated that the presence of T. sp. promotes Q235 carbon steel corrosion. Surface analyses results showed that heterogeneous adhesion is a typical character for T. sp. biofilm on surface of Q235 carbon steel, and pitting corrosion is induced. The corrosion mechanism model of Q235 carbon steel in air-saturated seawater containing T. sp. is proposed through surface micromorphology analyses, composition determination and current distribution.

Helium and Argon Isotopes in the Fe-Mn Polymetallic Crusts and Nodules from the South China Sea: Constraints on Their Genetic Sources and Origins

In this study, the He and Ar isotope compositions were measured for the Fe-Mn polymetallic crusts and nodules from the South China Sea (SCS), using the high temperature bulk melting method and noble gases isotope mass spectrometry. The He and Ar of the SCS crusts/nodules exist mainly in the Fe-Mn mineral crystal lattice and terrigenous clastic mineral particles. The results show that the 3He concentrations and R/RA values of the SCS crusts are generally higher than those of the SCS nodules, while 4He and 40Ar concentrations of the SCS crusts are lower than those of the SCS nodules. Comparison with the Pacific crusts and nodules, the SCS Fe-Mn crusts/nodules have lower 3He concentrations and 3He/4He ratios (R/RA, 0.19 to 1.08) than those of the Pacific Fe-Mn crusts/nodules, while the 40Ar/36Ar ratios of the SCS samples are significantly higher than those of the Pacific counterparts. The relatively low 3He/4He ratios and high 40Ar concentrations in the SCS samples are likely caused by terrigenous detrital input with high radiogenic 4He and 40Ar contents. The SCS crusts and nodules have shorter growth periods, implying that in situ post-formation radiogenic 3He, 4He and 40Ar produced by decay of U, Th and K have no effect on their isotope compositions. Thus, the SCS crusts/nodules inherited the noble gases characteristics of their sources. Helium and Ar isotope compositions in the SCS Fe-Mn crusts and nodules reflect the product of an equilibrium mixture between air-saturated seawater and radiogenic components during their growth, while the partial 3He excess in some SCS samples may represent a little mantle-derived origin. The different He and Ar isotope compositions of the Fe-Mn crusts and nodules between the South China Sea and the Pacific Ocean are due to their different sources and genetic processes. The characteristics of He and Ar isotope compositions in the SCS polymetallic crusts and nodules are similar to the properties of hydrogenetic Fe-Mn oxide/hydroxide precipitates, which reflects mainly the product of an equilibrium mixture between air-saturated seawater and radiogenic components.

Noble gases in sulfide deposits of modern deep-sea hydrothermal systems: Implications for heat fluxes and hydrothermal fluid processes

Studies of noble gases in seafloor sulfide deposits are an important tool for understanding the origin of ore-forming fluids, both enabling the determination of noble gas sources and revealing the degree of fluid–rock interaction and mantle degassing. The noble gas concentrations and isotopic compositions of 27 sulfide, 3 sulfate, and 2 opal mineral aggregate samples have been studied in different hydrothermal fields from the East Pacific Rise, Mid-Atlantic Ridge, Central Indian Ridge, Southwest Indian Ridge, and North Fiji Back-Arc Basin. The helium concentrations and isotopic ratios in the sulfide aggregate samples are variable (4He 0.12 to 22×10−8cm3 STP/g; 3He/4He ~0.6 to 10.4 Ra), and most of the sulfide helium concentrations are higher than those in the opal mineral samples (4He 0.017 and 0.028×10−8cm3 STP/g), suggesting that the low-temperature fluids have lost their mantle helium during cooling. The helium of high (>7 Ra), medium (1–7 Ra), and low (≈1 Ra) 3He/4He ratio samples is derived mainly from the MORB or OIB mantle by magma degassing, from mixing between hydrothermal fluid and seawater during ore-forming processes, and from ambient seawater, respectively. The high 3He/4He ratios (>7 Ra) of sulfides imply that high-temperature sulfides retain the helium isotopic compositions of the primary hydrothermal fluid, whereas low-temperature sulfides, sulfates, and opal minerals do not.The neon, argon, krypton, and xenon concentrations in the sulfide aggregate samples are also variable; in most of the sulfide aggregates, they are significantly lower than in the sulfate and opal mineral samples. It is known that barite and opal minerals are characteristic of low-temperature (<200°C) paragenetic associations, indicating that heavier noble gases (Ne, Ar, Kr and Xe) are enriched under low-temperature conditions. Most of the sulfide, sulfate and opal mineral aggregate samples possess heavy noble gas elemental abundances similar to those of air-saturated seawater and Ne, Ar, and Xe isotopic compositions that span narrow ranges around atmospheric values, an observation which is most easily explained by the dominance of a seawater-derived component.In addition, based on the calculated helium/heat ratios, global helium and heat fluxes to high-temperature hydrothermal vents are approximately 0.05–6×104kg per year and 0.1–12×1012W, meaning that roughly 0.3% of ocean heat is supplied by seafloor high-temperature hydrothermal activity.

Noble gases (Ar, Kr, Xe) and halogens (Cl, Br, I) in fluid inclusions from the Athabasca Basin (Canada): Implications for unconformity-related U deposits

The formation of unconformity-related uranium deposits in the Proterozoic Athabasca Basin (Canada) involved basin-scale circulation of U-bearing brines during high-grade diagenesis (150–200°C) at ∼1.6–1.5Ga. The UO2 ores occur both sides of the unconformity and are associated with extensive brecciation and illite–sudoite–dravite alteration. Quartz and dolomite cementing veins and breccias are associated with alteration and mineralisation and contain a fairly uniform population of fluid inclusions characterised by variable Na:Ca and salinities of 25–35wt.% salts and high U concentrations of up to 600ppm U. In order to further constrain the origin of these U-rich brines, we analysed the naturally occurring isotopes of Ar, Kr and Xe, together with halogens (Cl, Br and I), K, Ca and U in irradiated quartz and dolomite samples containing representative fluid inclusions. This was achieved by the noble gas method for halogen measurement (extended 40Ar–39Ar methodology) using a combination of noble gas extraction techniques.The fluid inclusions opened by crushing quartz and dolomite samples in vacuum have similar molar Br/Cl ratios of 5.8×10−3 to 10.4×10−3, and molar I/Cl ratios of 1.8×10−6 to 8.2×10−6. These compositions lie over the top half of the modern-day seawater evaporation trajectory, consistent with the fluids deriving the bulk of their salinity by subaerial evaporation of seawater, beyond the point of halite saturation. The I/Cl ratios are much lower than is typical of fluids that have interacted with I-rich organic matter present in many sedimentary basins or fluid inclusions found in Mississippi Valley type (MVT) Pb–Zn ore deposits. This is significant because provided the U-rich fluid inclusions are representative of the ore-stage fluids, the low I/Cl ratios of the fluid inclusions do not favour fluid interaction with organic matter (or hydrocarbons), as a major process for localising U mineralisation.The majority of samples contain fluid inclusions with age-corrected 40Ar/36Ar of between the modern atmospheric value of ∼300 and 450. These values are considered representative of the fluid's initial composition and are typical of upper crustal sedimentary formation waters. The fluid inclusions non-radiogenic 84Kr/36Ar and 129Xe/36Ar ratios are slightly enriched in 129Xe relative to air and the fluid inclusions are estimated to contain 0.5–17.3×10−10molg−136Ar which is up to twenty times the 36Ar concentration of air-saturated seawater. The data are interpreted to reflect acquisition of atmospheric noble gases from sedimentary rocks and suggest acquisition of radiogenic 40Ar within K-rich basement rocks, that would have been an important source of excess 40Ar, was limited by temperatures of less than 200°C.Taken together the halogen and noble gas composition of the U-bearing fluid inclusions are strongly controlled by subaerial evaporation and subsequent interaction with sedimentary rocks, showing that low temperature evaporitic brines dominated the mineralising system. Mineralisation is unlikely to have been triggered by fluid interaction with organic matter, or mixing with voluminous basement-derived fluids; however, the data do not completely preclude a role for volumetrically minor fluid or gas phases introduced by deep-seated basement faults preferentially located at the sites of mineralisation.

Hypoxia impairs visual acuity in snapper (Pagrus auratus)

We investigated the effect of environmental hypoxia on vision in snapper (Pagrus auratus). Juvenile snapper inhabit estuarine environments where oxygen conditions fluctuate on a seasonal basis. Optomotor experiments demonstrated that visual acuity is impaired by environmental hypoxia, but not until levels approach the critical oxygen tension (P crit) of this species (around 25% air-saturated seawater). In 100, 80, and 60% air-saturated seawater, a positive optomotor response was present at a minimum separable angle (M SA) of 1°. In 40% air-saturated seawater, vision was partially impaired with positive responses at M SAs of 2° and above. However, in 25% air-saturated seawater, visual acuity was seriously impaired, with positive responses only present at M SAs of 6° and above. Snapper were found to possess a choroid rete, facilitating the maintenance of high ocular oxygen partial pressures (PO2) during normoxia and moderate hypoxia (PO2, between 269 and 290 mmHg). However, at 40 and 25% water oxygen saturation, ocular PO2 was reduced to below 175 mmHg, which is perhaps linked to impairment of visual acuity in these conditions. The ability to preserve visual function during moderate hypoxia is beneficial for the maintenance of a visual lifestyle in the fluctuating oxygen environments of estuaries.

The hypoxia avoidance behaviour of juvenile Atlantic cod (Gadus morhua L.) depends on the provision and pressure level of an O2 refuge

The frequency of low O2 (hypoxia) has increased in coastal marine areas but how fish avoid deleterious water masses is not yet clear. To assess whether the presence and oxygen pressure (PO2) level of an O2 refuge affects the hypoxia avoidance behaviour of fish, individual Atlantic cod (Gadus morhua L.) were exposed to a range of O2 choices in a 2-way choice chamber at 11.4°C over two different experiments. Cod in the first experiment were allowed access to a fixed O2 refuge (fully air-saturated seawater) whilst oxygen pressure (PO2) on the other side was reduced in steps to a critically low level, i.e. 4.3 kPa—a point where cod can no longer regulate O2 consumption. Under these conditions, cod did not avoid any level of hypoxia and fish swimming speed also remained unchanged. In contrast, strong avoidance reactions were exhibited in a second experiment when fish were again exposed to 4.3 kPa but the safety, i.e. PO2, of the refuge was reduced. Fish not only spent less time at 4.3 kPa as a result of fewer sampling visits but they also swam at considerably slower speeds. The presence of an avoidance response was thus strongly related to refuge PO2 and it is unlikely that cod, and possibly other fish species, would enter low O2 to feed in the wild if a sufficiently safe O2 refuge was not available. It is therefore hypothesized that the feeding range of fish may be heavily compressed if hypoxia expands and intensifies in future years.

Oxidation of copper(I) in seawater at nanomolar levels

The oxidation and reduction of nanomolar levels of copper in air-saturated seawater and NaCl solutions has been measured as a function of pH (7.17–8.49), temperature (5–35 °C) and ionic strength (0.1–0.7 M). The oxidation rates were fitted to an equation valid at different pH and ionic strength conditions in sodium chloride and seawater solutions: log k (NaCl) = 5.221 + 0.609 pH − 1915 / T − 1.818 I + 0.408 I log k (sw) = 5.036 + 0.514 pH − 1765 / T − 1.101 I + 0.233 I . The reduction of Cu(II) was studied in both media for different initial concentrations of copper(II). When the initial Cu(II) concentration was 200 nM, the copper(I) productions were 20% and 9% for NaCl and seawater, respectively. The effect of speciation of copper(I) reduced from Cu(II) on the rates was studied. The Cu(I) speciation is dominated by the CuCl 2 − species. On the other hand, the neutral chloride CuCl species dominates the Cu(I) oxidation in the range of 0.1 M to 0.7 M chloride concentrations.

Changes in fluid geochemistry and physico-chemical conditions of geothermal systems caused by magmatic input: The recent abrupt outgassing off the island of Panarea (Aeolian Islands, Italy)

Hydrothermal systems and related vents can exhibit dramatic changes in their physico-chemical conditions over time as a response to varying activity in the feeding magmatic systems. Massive steam condensation and gas scrubbing processes of thermal fluids during their ascent and cooling cause further compositional changes that mask information regarding the conditions evolving at depth in the hydrothermal system. Here we propose a new stability diagram based on the CO 2-CH 4-CO-H 2 concentrations in vapor, which aims at calculating the temperatures and pressures in hydrothermal reservoirs. To filter gas scrubbing effects, we have also developed a model for selective dissolution of CO 2-H 2S-N 2-CH 4-He-Ne mixtures in fresh and/or air-saturated seawater. This methodology has been applied to the recent (November 2002) crisis that affected the geothermal field off the island of Panarea (Italy), where the fluid composition and fluxes have been monitored for the past two decades. The chemical and isotopic compositions of the gases suggest that the volatile elements originate from an active magma, which feeds a boiling saline solution having temperatures of up to 350°C and containing ≈12 mol% CO 2 in vapor. The thermal fluids undergo cooling and re-equilibration processes on account of gas-water-rock interactions during their ascent along fracture networks. Furthermore, steam condensation and removal of acidic species, partial dissolution in cold air-saturated seawater and stripping of atmospheric components, affect the composition of the geothermal gases at shallow levels. The observed geochemical variations are consistent with a new input of magmatic fluids that perturbed the geothermal system and caused the unrest event. The present-state evolution shows that this dramatic input of fluids is probably over, and that the system is now tending towards steady-state conditions on a time scale of months.

Measurement of Noble Gas Solubility in Seawater Using a Quadrupole Mass Spectrometer

A quadrupole-based mass spectrometric system for determining noble gas (He, Ne, Ar, Kr and Xe) abundances in a liquid sample has been developed and applied to seawater equilibrated with the atmosphere at several temperatures. After known amounts of isotopic spikes (22Ne, 36Ar, 86Kr and 124Xe) were introduced into the preparation vacuum line, dissolved gases were extracted from seawater and well mixed with the spikes by ultrasonic vibration. Noble gases were purified using three-stage hot Ti getters and separated by two activated charcoal traps held at low temperature (liquid nitrogen and dry ice—ethanol). Noble gas abundances were measured by a relatively inexpensive quadrupole mass spectrometer based on the isotope dilution technique. Precisions obtained by repeated measurements for He, Ne, Ar, Kr and Xe are 1.5%, 0.4%, 0.4%, 0.4% and 0.6%, respectively. Noble gas abundances in air-saturated seawater at eight temperature steps (1.0°C, 5.5°C, 10.0°C, 14.4°C, 17.0°C, 21.3°C, 24.6°C, and 29.6°C) were measured using the analytical system. The overall variation of the abundances with temperature agrees well with those of NaCl brines reported in the literature. We propose here new constants to fit observed data to empirical equation of noble gas solubility in seawater with its temperature variation.

Helium isotopes of seawater in adjacent sea of Nansei Islands, Southwest Japan

We have measured helium isotopic ratios of 43 water samples with various depths collected in Eastern East China Sea and Northwestern Philippine Sea, adjacent region of Nansei Islands, Southwestern Japan. The 3He/4He ratios vary significantly from 0.994 Ratm to 1.242 Ratm where Ratm is the atmospheric ratio of 1.39 × 10-6. Mid-depth (750–1500 m) samples in this study would be affected by the source of subduction-type mantle helium in the Okinawa Trough. Noble gas abundances (neon, argon, krypton and xenon) were measured in 24 water samples with various depths collected in Northwestern Pacific Ocean and Northwestern Philippine Sea (Nansei Trench). Neon abundances show slight excess relative to air saturated seawater at ambient temperature and salinity. This may be due to either air bubble effect or contamination during the sampling. When these effects are corrected using the neon anomaly, heavier noble gas abundances (argon, krypton and xenon) of samples with the temperature higher than 5°C (shallower than 500 m) agree well with those of calculated air saturated seawater, while the lower temperature samples (deeper than 500 m) indicate anomaly of −7% to +10%.

Effects of sessile Protozoa on intracapsular oxygen tension and embryonic shell calcification in the muricid Chorus giganteus

Clusters of egg capsules deposited by some common marine Mollusca may suffer problems of a low diffusive oxygen supply to the embryos they contain, especially if the capsules are exposed to hypoxic seawater or attachment and growth of marine biofouling organisms. The present study was undertaken to determine the effects of severe biofouling by sessile Protozoa on intracapsular oxygen tension (IPO 2 ) and the development of embryos contained in the egg capsules of the muricid snail Chorus giganteus. We also investigated the effects of ambient oxygen tension (EPO2) on IPO 2 . The presence of sessile Protozoa attached to the outer wall of the egg capsules significantly reduced the IPO 2 compared to capsules not fouled by Protozoa. Clean capsules containing embryos showed an IPO 2 of about 105 mm Hg, compared with about 92 mm Hg for protozoan-fouled capsules when both were immersed in air-saturated seawater at 12°C. The embryos in capsules without Protozoa grew normally, hatching in about 70 d as veliconch larvae, whereas the development of larvae in protozoan-fouled capsules showed impairment of shell formation and delay in hatching for up to 5 mo. Pre-hatch embryos at 60 d measured about 922 μm and had an ash content near 18 μg embryo -1 embryos in capsules covered by micro-organisms measured only about 783 pm, with an ash content of about 3 μg embryo -1 over the same time period. Our study suggested that the lack of larval calcification observed in the presence of sessile Protozoa on the outer wall of the egg capsules was probably related to reduced IPO 2 . Similarly, any factor reducing oxygen supply to encapsulated embryos (i.e. exposure to water masses with low oxygen content, biofouling, reduced water movement) could impair embryonic development, a significant phenomenon thus far not reported in C. giganteus.

Solid stainless steel for MSF once-through plants

A field test in a multi-stage flash (MSF) once-through plant has been evaluated. Six metallic construction materials, five stainless steels and one nickel base alloy, were exposed for a period of 28 months in the hot chlorinated and air saturated seawater stream of the first flash chamber at a temperature of 100°C. The lowest alloyed grades, i.e., type 316, S31726 (“317LMN”), and S31803 suffered pitting and crevice corrosion while the highly alloyed grade S31254 suffered superficial crevice corrosion. The most highly alloyed stainless steel S32654 and the nickel base alloy N06625 were fully resistant. No material suffered stress corrosion cracking. A 6Mo grade such as S31254 is a good choice for the first stage of evaporator vessels. The first six stages of the plant where the test was performed are made of solid S31254.

Fe sulfide formation due to seawater-gas-sediment interaction in a shallow-water hydrothermal system at Lihir Island, Papua New Guinea

Fe sulfide minerals are forming in the shallow-water hydrothermal system in Luise Harbor, Lihir Island, Papua New Guinea, due to the interaction of hydrothermal gas+ or -liquid, seawater, and Fe-rich sediments. Upon contact with oxygenated seawater, hydrothermal H 2 S is oxidized and forms H 2 SO 4 leading to the simultaneous dissolution of primary, Fe-rich sediment grains and the neoformation of mainly marcasite and pyrite. They are present as alternating colloform layers, as framboidal aggregates in vugs, or they replace organic fragments, primary olivine and primary magnetite. Deposition of either marcasite or pyrite appears to reflect variations in acidity due to varying admixture of air-saturated seawater. The gas phase is composed of mainly CO 2 , N 2 , and H 2 S. Assuming equilibration of the gases dissolved in a liquid phase and preservation of equilibrium CH 4 /CO 2 , the CH 4 -CO 2 equilibrium temperature is approximately 310 degrees + or -20 degrees C.

Corrosion resistance of HVOF WC–Co and TiC/Ni–Ti coatings sprayed on commercial steel

Corrosion, erosion, and abrasion damage arefrequently found in equipment used in service in the oil and gas industries. This represents a challenge to materials engineers because of the deterioration of equipment and increased maintenance costs. Much work is being done on the evolution of corrosion of different types of coatings. The aim of the present work is to study the corrosion behaviour of two different coatings sprayed using high velocity oxyfuel technology. A commercial steel was coated with a CDS 1927 (WC–12Co) or TiC/Ni–Ti powder using a Plasma-Technik CDS–100 thermal spray gun. The powder was sprayed on to a cylindrical specimen 25·4 mm in diameter and 25·4 mm high. The corrosion potential v. time and potentiodynamic polarisation were studied inan ASTM standard cell with three electrodes. Air saturated seawater was used as the electrolyte.

A reduced dissolved oxygen test system for marine organisms

A flow-through test system was designed to examine minimum dissolved oxygen (D.O.) requirements of marine animals. The system provides up to six treatment concentrations between 0.3 mg D.O./l and saturation. Sea water is degassed in a vacuum-evacuated packed column and the treatment concentrations are controlled electronically by time-proportional mixing of water from degassed and air-saturated seawater reservoirs. The system has proven capable of reliable continuous operation for test periods as long as 28 days, with the reduced D.O. treatments controlled to ±0.15 mg/l s.d. at flows ≥10 ml/min and to ±0.25 mg/l s.d. at lower flow rates.

Use of DC Electrochemical Methods for Evaluation of Paint Films on Steel, Aluminum, and Zinc

Abstract Degradation of paints that were applied on steel, aluminium, and zinc and exposed to air-saturated seawater has been studied by using direct current (DC) electrochemical methods and by visual examination of long-term exposed specimens. The DC measurements were performed on surfaces with a continuous paint film, and the long-term specimens were polarized by a defect in the paint film. The DC measurements on coated aluminium, steel, and zinc have been found to give information about the mechanism of corrosion. The results illustrate the importance of the properties of the metal substrate and of the paint film. Coated steel galvanically coupled to bare steel was found to have a high potential and, hence, to act as a cathode vs bare steel. For coated aluminium, however, initiation of corrosion at the metal/coating interface was found to give a much lower potential. The behavior of coated zinc was found to be similar to that of coated steel. The potential was high compared to bare zinc, which means th...

Two methods for the assessment of the oxygen content of small volumes of seawater

Modified micro-Winkler and couloximetric methods are described for the measurement of oxygen in small volumes of water. The former uses a sample size of 1 cm 3, while the latter is routinely run with 25-μl samples. Both are accurate, producing results <2% above and 4% below expected values calculated from two previously published sets of tables for the oxygen content of air-saturated seawater. They are also precise assessments, with the se of the micro-Winkler results being 0.23% of the mean of five repeated measurements, while the same figure for the couloximeter is 0.21%. They overcome many of the problems associated with standard methods of measuring oxygen content, such as temperature, salinity and pressure-related effects as well as obviating the need for relatively large quantities of water. Being an essentially inert system the couloximeter may be used for measuring the oxygen content of fluids which pose problems for other methods, such as blood and haemolymph. It is also an absolute method, requiring no calibration. These techniques have been used in the past for measuring oxygen consumption in polar marine invertebrates at temperatures below 0°C and temperate crustacean species.

Noble gases in vent water from the Juan de Fuca Ridge

Hydrothermal vent fluids collected with the DSRV Alvin from the southern limb of the Juan de Fuca Ridge are chemically unique, having chloride concentrations ~2 times ambient seawater. The same fluids contain noble gases in relative abundances like 2°C air-saturated seawater, the expected recharge composition. However, the absolute noble gas abundances are depleted by ~30% relative to seawater. The combination of very high chloride and moderately depleted noble gases appears to require the formation of a Cl-rich, gas-free brine by phase separation. This brine is mixed with recharge seawater at temperatures in excess of ~340°C and, therefore, deep in the hydrothermal system.