Cold Seawater Research Articles

Chimneys in Paleozoic massive sulfide mounds of the Urals VMS deposits: Mineral and trace element comparison with modern black, grey, white and clear smokers

In the Urals, a wide range of well-preserved chimneys are found in VMS deposits, which are associated with ultramafic (Atlantic type: Dergamysh), mafic (Cyprus type: Buribay), bimodal mafic (Uralian type: Yubileynoye, Sultanovskoye, Yaman-Kasy, Molodezhnoye, Uzelga-4, Valentorskoye) and bimodal felsic (Kuroko or Baymak type: Oktyabrskoye, Tash-Tau, Uselga-1, Talgan, Alexandrinskoye) sequences. Chimneys have also been found in the Safyanovskoye deposit (Altay type) that is hosted by intercalated felsic lavas and carbonaceous shales. A combination of geological, mineralogical and trace element data provide a general outline for comparison between chimneys from the Urals deposits and modern vent sites. The chimneys from the Dergamysh deposit show a broad affinity with those from the Rainbow and other vent sites associated with serpentinites of the Mid-Atlantic Ridge. The chimneys from the Buribay deposit are similar to the black smokers of the EPR vent sites including the scarcity of rare minerals. The chimneys from the Urals type of the VMS deposits show some similarities with grey smokers from the Brother Volcano and PACMANUS sites. The chimneys from the Baymak type of the VMS deposits resemble grey and white smokers of the PACMANUS and grey smokers of the Suiyo vent sites. The chimneys from the Safyanovskoye deposit are similar to the black and clear smokers from the Okinawa Trough. Mineral assemblages are controlled by the combination of host rock composition and physico-chemical conditions of the ore-forming processes. Amount of colloform pyrite, isocubanite and pseudomorphic pyrite and marcasite after pyrrhotite decreases in the chimneys across the range from ultramafic and mafic to felsic-hosted deposits and is concomitant with increase in the contents of sphalerite, galena, bornite, fahlores, native gold and barite across this range. The chimneys from the Urals type contain abundant tellurides and sulfoarsenides, while these minerals are rare (except for hessite) in the Baymak type deposits. In the same range, the buffering capacity of host rocks decreases in contrast to the increase in ƒS2 and ƒO2. With the exception of the Safyanovskoye deposit, trace element assemblages in chalcopyrite vary to reflect the host rock: ultramafic (high Se, Sn, Co, Ni, Ag and Au)→mafic (high Co, Se, Mo and low Bi, Au and Pb)→bimodal mafic (high Te, Au, Ag, Bi, Pb, Co, moderate Se, and variable As and Sb)→bimodal felsic (high As, Sb, Mo, Pb, moderate Bi, and low Co, Te and Se). In sphalerite of the same range, the contents of Bi, Pb, Ag, Au and Sb increase versus Fe, Se and Сo. The variations in trace elements in colloform pyrite coincide with these changes. The specific mineral changes in the local ranges from Cu- to Zn-rich chimneys in each VMS deposit are similar to the general changes in the range of host rock classes of the deposits. However, the local T, ƒS2 and ƒO2 changes can broadly be interpreted in terms of contribution of variable oxygenated cold seawater to the subseafloor and seafloor hydrothermal processes.

Using offshore wind technology for large-scale cooling applications

A system which makes use of offshore wind energy to directly provide large-scale cooling through the exploitation of cold deep seawater below the thermocline is proposed. This system is composed of a hydraulic wind turbine directly coupled to an air cycle machine. A 4-year case study of this conceptual system operating in a central Mediterranean region was carried out, with results showing that such system could operate efficiently during instances of high cooling demands. In fact, it was established that during such instances, the proposed system could lead to an increased cooling capacity when compared to conventional refrigerant-based chillers operated with surface seawater.

Fluid inclusion and stable isotopic constraints on fluid sources and evolution of the Luojiahe Cu deposit in the southern margin of the North China Craton

The Luojiahe Cu deposit in the Zhongtiaoshan region is located in the southern margin of the North China Craton. The orebodies are hosted in the mafic volcanic-sedimentary sequences of the metamorphosed (greenschist-facies) Neoarchean Songjiashan Group. The Luojiahe Cu mineralization can be divided into the primary volcanogenic massive sulfide (VMS) mineralization stage (Stage I, banded or stockwork ores) and the subsequent metamorphic remobilization stage (Stage II, coarse-vein ores).Three types of quartz selected for fluid inclusion (FI) studies were collected from the Stage I banded (Q1) and stockwork (Q2) ores and Stage II coarse-vein (Q3) ores. Four types of FIs were identified: (1) liquid-rich FIs (L-type), (2) pure vapor and vapor-rich FIs (V-type), (3) daughter mineral-bearing FIs (S-type), and (4) CH4-H2O FIs (C-type). Systematical microthermometric and H-O isotopic studies show that the Stage I ore-forming fluids consist predominantly of high salinity evolved seawater (125–220°C; 23.9–27.9wt.% NaCl equiv.) and some magmatic-hydrothermal fluids (249–339°C; 34.5–42.2wt.% NaCl equiv.). The two fluid end-members are represented by the L-type FIs in Q1 and the S- and V-type FIs in Q2. The temperature- and salinity variation trends of the L-type FIs in Q1 indicate a mixing process between the hot evolved seawater and cold seawater at Stage I. Furthermore, the V- and S-type FI coexistence in Q2 and their microthermometric data suggest that fluid unmixing has occurred in original magmatic fluids at Stage I. In contrast, the Stage II ore-forming fluids consist of CH4-rich metamorphic fluids (192–350°C; 10.6–43.2wt.% NaCl equiv.). Carbon isotopic analysis of the Stage II calcite (−4.58 to −10.83‰) and graphite (−32.01 to −39.16‰) in the ore-hosting chlorite schist indicates that the metamorphic ore-forming fluids had exchanged carbon isotope with graphite. The generation of CH4 may have resulted from the interaction between H2O (released by metamorphic devolatilization) and graphite. The continuous consumption of H2O in the hydrothermal fluid system may have increased the fluid salinity and triggered fluid unmixing in the CH4-NaCl-H2O system. In addition, the VMS metallogenic environment is generally favorable for microbial communities. It is considered that the graphite at Luojiahe may have been derived from sedimentary organic matter formed in seafloor hydrothermal vent systems, as also supported by carbon isotopic data.We propose that at Stage I, the main mineralization may have been resulted from 1) fluid mixing of hot evolved seawater and cold seawater in the near-surface environment; and 2) fluid unmixing caused by the percolation of magmatic fluids into syn-volcanic faults, forming the stockwork ores. At Stage II, the interaction between H2O and graphite may have resulted in the reduction of ore-forming fluids and Cu precipitation, and fluid unmixing in the CH4-NaCl-H2O system may have further promoted the Cu mineralization.

Changes in the Vibrio harveyi Cell Envelope Subproteome During Permanence in Cold Seawater

Previous work demonstrated that physiological, morphological, and gene expression changes as well as the time-dependent entry into the viable but not culturable (VBNC) state are used by Vibrio species to survive and cope with diverse stress conditions including seasonal temperature downshifts and starvation. To learn more about the nature and specific contribution of membrane proteins to cell adaptation and survival, we analyzed variations in the protein composition of cell envelope and related them to morphological and physiological changes that were taking place during the long-term permanence of Vibrio harveyi in seawater microcosm at 4°C. We found that after 21days of permanence, nearly all population (ca. 99%) of V. harveyi acquired the VBNC phenotype. Although the size of V. harveyi cells gradually decreased during the incubation time, we found that this morphological change was not directly related to their entry into the VBNC state. Our proteomic study revealed that the level of membrane proteins playing key roles in cellular transport, maintenance of cell structure, and in bioenergetics processes remained unchanged along starvation at low temperature, thus suggesting that V. harveyi might need these proteins for the long-term survival and/or for the resuscitation process. On a contrary, the level of two proteins, elongation factor Tu (EF-TU) and bacterioferritin, greatly increased reaching the maximal values by the end of the incubation period. We further discuss the above data with respect to the putative roles likely exerted by membrane proteins during transition to and maintaining of the VBNC state.

Picturing thermal niches and biomass of hydrothermal vent species

In community ecology, niche analysis is a classic tool for investigating species׳ distribution and dynamics. Components of a species׳ niche include biotic and abiotic factors. In the hydrothermal vent ecosystem, although composition and temporal variation have been investigated since these deep-sea habitats were discovered nearly 40 years ago, the roles and the factors behind the success of the dominant species of these ecosystems have yet to be fully elucidated. In the Lucky Strike vent field on the Mid-Atlantic Ridge (MAR), the dominant species is the mussel Bathymodiolus azoricus. Data on this species and its associated community were collected during four oceanographic cruises on the Eiffel Tower edifice and integrated in a novel statistical framework for niche analysis. We assessed the thermal range, density, biomass and niche similarities of B. azoricus and its associated fauna.Habitat similarities grouped mussels into three size categories: mussels with lengths ranging from 0.5 to 1.5cm, from 1.5 to 6cm, and mussels longer than 6cm. These size categories were consistent with those found in previous studies based on video imagery. The three size categories featured different associated fauna. The thermal range of mussels was shown to change with organism size, with intermediate sizes having a broader thermal niche than small or large mussels. Temperature maxima seem to drive their distribution along the mixing gradient between warm hydrothermal fluids and cold seawater. B. azoricus constitutes nearly 90% of the biomass (in g dry weight /m2) of the ecosystem. Mean individual weights were calculated for 39 of the 79 known taxa on Eiffel Tower and thermal ranges were obtained for all the inventoried species of this edifice. The analysis showed that temperature is a suitable variable to describe density variations among samples for 71 taxa. However, thermal conditions do not suffice to explain biomass variability. Our results provide valuable insights into mussel ecology, biotic interactions and the role of B. azoricus in the community.

In situ Dynamics of O2, pH, Light, and Photosynthesis in Ikaite Tufa Columns (Ikka Fjord, Greenland)-A Unique Microbial Habitat.

The Ikka Fjord (SW Greenland) harbors a unique microbial habitat in the form of several hundred submarine tufa columns composed of ikaite, a special hexahydrate form of calcium carbonate that precipitates when alkaline phosphate- and carbonate-enriched spring water seeping out of the sea floor meets cold seawater. While several unique heterotrophic microbes have been isolated from the tufa columns, the microbial activity, and the boundary conditions for microbial growth in ikaite have remained unexplored. We present the first detailed in situ characterization of the physico-chemical microenvironment and activity of oxygenic phototrophs thriving within the ikaite columns. In situ underwater microsensor measurements of pH, temperature, and irradiance in the porous ikaite crystal matrix, revealed an extreme microenvironment characterized by low temperatures, strong light attenuation, and gradients of pH changing from pH 9 at the outer column surface to above pH 10 over the first 1–2 cm of the ikaite. This outer layer of the freshly deposited ikaite matrix contained densely pigmented yellow and green zones harboring a diverse phototrophic community dominated by diatoms and cyanobacteria, respectively, as shown by amplicon sequencing. In situ O2 measurements, as well as underwater variable chlorophyll fluorescence measurements of photosynthetic activity, demonstrated high levels of oxygenic photosynthesis in this extreme gradient environment with strong irradiance-driven O2 dynamics ranging from anoxia to hyperoxic conditions in the ikaite matrix, albeit the local formation of gas bubbles buffered the day-night dynamics of O2 in the tufa columns. The microbial phototrophs in the ikaite matrix are embedded in exopolymers forming endolithic biofilms that may interact with mineral formation and cementing of ikaite crystals.

Occurrences and distribution of “invisible” precious metals in sulfide deposits from the Edmond hydrothermal field, Central Indian Ridge

Here, we report the first documented occurrences of “invisible” gold and silver in seafloor sulfide deposits from an active hydrothermal system on the Central Indian Ridge. A detailed mineralogical and geochemical study of polymetallic sulfides from the Edmond vent field was conducted in order to identify controls on the distribution of precious metals. Bulk samples (N=18) contain up to 18.7ppm Au and 1450ppm Ag, with average concentrations of 2.3ppm Au and 218.9ppm Ag. Among them, several Zn-rich chimney fragments and anhydrite-dominated ore samples have higher contents of precious metals than Fe-Cu-rich massive sulfides and silica-rich hydrothermal precipitates. Native gold grains are mainly associated with sphalerite, anhydrite, barite and Fe-oxyhydroxides. Abundant submicroscopic Au-Ag alloys tend to occur along grain boundaries between Cu-Fe sulfides and tennantite, or close to the rims of Fe-poor sphalerite. In contrast to primary electrum with high Ag/Au ratios, the absence of detectable silver in high-purity gold indicates that secondary Au enrichment has probably occurred after a direct co-precipitation with Zn-rich mineral assemblages upon cooling and mixing of vent fluids with cold seawater. A suite of late-stage Ag-rich phases, including argentotennantite, pearceite and acanthite, occur as crack-filling veinlets and patches in low-temperature fahlores, or as tiny inclusions enclosed by pyrite, chalcopyrite and colloform sphalerite. By using HRTEM combined with HAADF-STEM imaging, we have found out that silver is also present in significant quantities as discrete colloidal nanoparticles in tennantite. Minor native copper is closely associated with altered chalcopyrite, sphalerite and covellite, exhibiting signs of dissolution, recrystallization and reprecipitation. Extensive hydrothermal reworking resulted from a long history of high-temperature venting in this field, together with post-depositional supergene replacement processes (involving oxidation, leaching or coupled dissolution-reprecipitation mechanisms facilitated by a permeable porosity generated in primary Cu-Fe sulfides) are considered to be important for the remobilization and local reconcentration of early-formed precious metals, and may have been responsible for the formation of relatively coarse-grained native gold or silver within recrystallized massive sulfides and chimney debris.

Implications of Limited Thermophilicity of Nitrite Reduction for Control of Sulfide Production in Oil Reservoirs.

Nitrate reduction to nitrite in oil fields appears to be more thermophilic than the subsequent reduction of nitrite. Concentrated microbial consortia from oil fields reduced both nitrate and nitrite at 40 and 45°C but only nitrate at and above 50°C. The abundance of the nirS gene correlated with mesophilic nitrite reduction activity. Thauera and Pseudomonas were the dominant mesophilic nitrate-reducing bacteria (mNRB), whereas Petrobacter and Geobacillus were the dominant thermophilic NRB (tNRB) in these consortia. The mNRB Thauera sp. strain TK001, isolated in this study, reduced nitrate and nitrite at 40 and 45°C but not at 50°C, whereas the tNRB Petrobacter sp. strain TK002 and Geobacillus sp. strain TK003 reduced nitrate to nitrite but did not reduce nitrite further from 50 to 70°C. Testing of 12 deposited pure cultures of tNRB with 4 electron donors indicated reduction of nitrate in 40 of 48 and reduction of nitrite in only 9 of 48 incubations. Nitrate is injected into high-temperature oil fields to prevent sulfide formation (souring) by sulfate-reducing bacteria (SRB), which are strongly inhibited by nitrite. Injection of cold seawater to produce oil creates mesothermic zones. Our results suggest that preventing the temperature of these zones from dropping below 50°C will limit the reduction of nitrite, allowing more effective souring control. Nitrite can accumulate at temperatures of 50 to 70°C, because nitrate reduction extends to higher temperatures than the subsequent reduction of nitrite. This is important for understanding the fundamentals of thermophilicity and for the control of souring in oil fields catalyzed by SRB, which are strongly inhibited by nitrite.

The fertile physics of chemical gardens

Many a child has enjoyed watching the gardens grow; many a physicist has puzzled over the transformation of self-organized, nonequilibrium patterns into permanent structures.

Gelation of Soy Milk with Hagfish Exudate Creates a Flocculated and Fibrous Emulsion- and Particle Gel.

Hagfish slime is an ultra dilute, elastic and cohesive hydrogel that deploys within milliseconds in cold seawater from a glandularly secreted exudate. The slime is made of long keratin-like fibers and mucin-like glycoproteins that span a network which entraps water and acts as a defense mechanism against predators. Unlike other hydrogels, the slime only confines water physically and is very susceptible to mechanical stress, which makes it unsuitable for many processing operations and potential applications. Despite its huge potential, little work has been done to improve and functionalize the properties of this hydrogel. To address this shortcoming, hagfish exudate was mixed with a soy protein isolate suspension (4% w/v) and with a soy emulsion (commercial soy milk) to form a more stable structure and combine the functionalities of a suspension and emulsion with those of the hydrogel. Hagfish exudate interacted strongly with the soy systems, showing a markedly increased viscoelasticity and water retention. Hagfish mucin was found to induce a depletion and bridging mechanism, which caused the emulsion and suspension to flocculate, making “soy slime”, a cohesive and cold-set emulsion- and particle gel. The flocculation network increases viscoelasticity and substantially contributes to liquid retention by entrapping liquid in the additional confinements between aggregated particles and protein fibers. Because the mucin-induced flocculation resembles the salt- or acid-induced flocculation in tofu curd production, the soy slime was cooked for comparison. The cooked soy slime was similar to conventional cooked tofu, but possessed a long-range cohesiveness from the fibers. The fibrous, cold-set, and curd-like structure of the soy slime represents a novel way for a cold coagulation and fiber incorporation into a suspension or emulsion. This mechanism could be used to efficiently gel functionalized emulsions or produce novel tofu-like structured food products.

Coupling of an offshore wind-driven deep sea water pump to an air cycle machine for large-scale cooling applications

A system for using offshore wind energy to directly provide large-scale cooling through the exploitation of cold deep seawater below thermocline formations is proposed. The concept is based on an offshore wind-driven hydraulic pump supplying high pressure deep seawater to a land based plant. This pressurised seawater is used to power a hydraulic turbine which drives an inverse Brayton air cycle machine, and is then diverted to a heat exchanger to cool the pressurised air prior to flowing back to the sea.A mathematical model for steady-state performance analysis of the proposed system under specified ambient conditions is presented. It was found that the system coefficient of performance was highest at low wind speeds and improved with increasing ambient temperature and humidity. This makes the system ideal for hot and humid climates. The availability of a sufficiently cold deep seawater resource was also found to be crucial for the viability of the system.

Diving bradycardia of elderly Korean women divers, haenyeo, in cold seawater: a field report.

The purpose of the present field study was to explore diving patterns and heart rate of elderly Korean women divers (haenyeo) while breath-hold diving in cold seawater. We hypothesized that the decreasing rate in heart rate of elderly haenyeos during breath-hold diving was greater and total diving time was shorter than those of young haenyeos from previous studies. Nine haenyeos participated in a field study [68 ± 10 yr in age, ranged from 56 to 83 yr] at a seawater temperature of 10 to 13 °C. Average total diving time including surface swimming time between dives was 253 ± 73 min (155–341 min). Total frequency of dives was 97 ± 28 times and they dived 23 ± 8 times per hour. All haenyeos showed diving bradycardia with a decreased rate of 20 ± 8% at the bottom time (101 ± 20 bpm) when compared to surface swimming time (125 ± 16 bpm) in the sea. Older haenyeos among the nine elderly haenyeos had shorter diving time, less diving frequencies, and lower heart rate at work (p<0.05). These reductions imply that haenyeos voluntarily adjust their workload along with advancing age and diminished cardiovascular functions.

Numerical investigation of heat transfer characteristics for Subsea Xmas tree assembly

This study focuses on the heat transfer characteristic of a horizontal subsea Xmas tree assembly at a high spatial resolution. Computational fluid dynamics (steady Reynolds-averaged Navier-Stokes) in combination with Low Reynolds number modelling (LRNM) is adopted for heat transfer analysis, which has been validated against a full scale underwater gate valve heat transfer experiment with good agreements. The characteristics of cold sea water flowing through the subsea tree, and of convection heat transfer between the subsea tree and ambient cold water are obtained. The typical “hot spots,” which have high Convection heat transfer coefficient (CHTC) and create great large amounts of heat loss, are numerically determined. Under the designed water depth, the effects of installation orientation, sea water velocity, and inner oil temperature on convection heat transfer are investigated as well. Such work is significant for thermal design of the subsea tree to increase structural reliability and flow assurance level.

Precipitation and growth of barite within hydrothermal vent deposits from the Endeavour Segment, Juan de Fuca Ridge

Hydrothermal vent deposits form on the seafloor as a result of cooling and mixing of hot hydrothermal fluids with cold seawater. Amongst the major sulfide and sulfate minerals that are preserved at vent sites, barite (BaSO4) is unique because it requires the direct mixing of Ba-rich hydrothermal fluid with sulfate-rich seawater in order for precipitation to occur. Because of its extremely low solubility, barite crystals preserve geochemical fingerprints associated with conditions of formation. Here, we present data from petrographic and geochemical analyses of hydrothermal barite from the Endeavour Segment of the Juan de Fuca Ridge, northeast Pacific Ocean, in order to determine the physical and chemical conditions under which barite precipitates within seafloor hydrothermal vent systems. Petrographic analyses of 22 barite-rich samples show a range of barite crystal morphologies: dendritic and acicular barite forms near the exterior vent walls, whereas larger bladed and tabular crystals occur within the interior of chimneys. A two component mixing model based on Sr concentrations and 87Sr/86Sr of both seawater and hydrothermal fluid, combined with 87Sr/86Sr data from whole rock and laser-ablation ICP-MS analyses of barite crystals indicate that barite precipitates from mixtures containing as low as 17% and as high as 88% hydrothermal fluid component, relative to seawater. Geochemical modelling of the relationship between aqueous species concentrations and degree of fluid mixing indicates that Ba2+ availability is the dominant control on mineral saturation. Observations combined with model results support that dendritic barite forms from fluids of less than 40% hydrothermal component and with a saturation index greater than ∼0.6, whereas more euhedral crystals form at lower levels of supersaturation associated with greater contributions of hydrothermal fluid. Fluid inclusions within barite indicate formation temperatures of between ∼120°C and 240°C during barite crystallization. The comparison of fluid inclusion formation temperatures to modelled mixing temperatures indicates that conductive cooling of the vent fluid accounts for 60–120°C reduction in fluid temperature. Strontium zonation within individual barite crystals records fluctuations in the amount of conductive cooling within chimney walls that may result from cyclical oscillations in hydrothermal fluid flux. Barite chemistry and morphology can be used as a reliable indicator for past conditions of mineralization within both extinct seafloor hydrothermal deposits and ancient land-based volcanogenic massive sulfide deposits.

Topsy-turvy: turning the counter-current heat exchange of leatherback turtles upside down.

Counter-current heat exchangers associated with appendages of endotherms feature bundles of closely applied arteriovenous vessels. The accepted paradigm is that heat from warm arterial blood travelling into the appendage crosses into cool venous blood returning to the body. High core temperature is maintained, but the appendage functions at low temperature. Leatherback turtles have elevated core temperatures in cold seawater and arteriovenous plexuses at the roots of all four limbs. We demonstrate that plexuses of the hindlimbs are situated wholly within the hip musculature, and that, at the distal ends of the plexuses, most blood vessels supply or drain the hip muscles, with little distal vascular supply to, or drainage from the limb blades. Venous blood entering a plexus will therefore be drained from active locomotory muscles that are overlaid by thick blubber when the adults are foraging in cold temperate waters. Plexuses maintain high limb muscle temperature and avoid excessive loss of heat to the core, the reverse of the accepted paradigm. Plexuses protect the core from overheating generated by muscular thermogenesis during nesting.

A SEMIPERMEABLE INTERFACE MODEL FOR THE GENESIS OF SUBSEAFLOOR REPLACEMENT-TYPE VOLCANOGENIC MASSIVE SULFIDE (VMS) DEPOSITS

Subseafloor replacement-style volcanogenic massive sulfide (VMS) deposits are a subset of VMS deposits where sulfides have replaced unconsolidated volcanic, volcano-sedimentary, and sedimentary material. These deposits are anomalously large and are important global sources of metals. They have distinct textures at the sulfide-ore interface, including bed-by-bed replacement of sedimentary layers, and typically fill void space between unconsolidated volcaniclastic detritus or fractures in flows or intrusions. At the microscale, metalbearing sulfides have partially to fully replaced framboidal (bacteriogenic) sulfides, or the framboidal sulfides have acted as nuclei upon which additional metalliferous massive sulfide is deposited. The textures presented are reconciled within a semipermeable interface model for replacement. In this model unconsolidated sediment, volcaniclastic rocks, or fractured coherent volcanic rocks provide a permeable to semipermeable interface that allowed ingress of cold seawater into the pore spaces of the stratigraphic sequence prior to and during lulls in hydrothermal activity. Seawater sulfate in the pore water is partially reduced by bacteria to provide reduced sulfur (H2S) as well as framboidal pyrite in the host sequence(s). The reduced sulfur and framboidal pyrite, as well as the cool pore water, provided a thermal, redox, and chemical gradient in which upwelling hydrothermal fluids interact. In such an environment rising hydrothermal fluids mix with cold water, not only at the seawater interface leading to exhalative sulfide deposition, but also in the subseafloor leading to sulfide precipitation via replacement. The upwelling hydrothermal fluids can also interact with bacterial H2S in the pore spaces of the unconsolidated material, resulting in additional subseafloor precipitation of metal sulfides. The fluids also result in replacement of framboidal pyrite nuclei pseudomorphous after the original framboidal masses. This semipermeable interface also favors enhanced zone refining, assuming the hydrothermal system is sufficiently long lived, leading to upgrading of the tenor of the sulfides with well-developed metal zoning, as observed in many ancient replacement-type deposits. Furthermore, the precipitation of a significant subseafloor sulfide mineralization results in greater trapping of metals from upwelling fluids and larger tonnage deposits with greater contained metal. This model may also be applicable to other replacement-type deposits in broadly similar geologic and hydrothermal environments (e.g., sediment-hosted and Irish-type Zn-Pb deposits). Additional, critical tests are required to validate and refute the model and potential tests are presented herein.

Diving bradycardia of elderly Korean women divers in cold seawater: a field report

Throughout the world, breath-hold diving has been reported in women divers in Korea (haenyeo) and Japan (ama), sponge divers in Greece, pearl divers in the South Pacific and shell divers in Australia. However, most of them have begun to use SCUBA (self-contained underwater breathing apparatus), whereas women divers in Korea and Japan have continued breath-hold diving. Since over 80% of haenyeos at present are in their sixties or older, it is predicted that breath-hold diving will cease to exist in a couple of decades. There is very little known about elderly haenyeos' cardiovascular changes. The purpose of the present study was to explore the diving patterns and heart rate of older Korean women divers while breath-hold diving in cold seawater.

Estimation of long-term drag performance of fouling control coatings using an ocean-placed raft with multiple dynamic rotors

An experimental setup was designed and built to estimate changes in the skin friction of fouling control coatings (FCC) over an extended period of time in conditions simulating the vast majority of ship profiles (regarding speed and activity) in the present market. The setup consisted of two separate parts: one aged FCCs directly in seawater in a dynamic manner by simulating the exposure condition of a ship’s hull, and a second, laboratory part measured the torque (drag) of aged coatings in a rotary setup. From the spring to the autumn of 2013 and 2014, four commercial FCCs were exposed for 53 weeks in Roskilde Fjord, Denmark, which is characterized by relatively cold seawater and a salinity of approximately 1.2 wt%. The in situ immersion seawater conditions consisted of five-week cycles divided into 2 weeks of static immersion and 3 weeks of dynamic immersion, during which time the cylinders were rotated at a tangential velocity of 8.1 knots. The skin friction was found to generally increase more during the static period, compared to the dynamic ones. Over the course of the entire exposure period, the skin friction of the investigated FCCs decreased in the following order: fluorinated fouling release coating (FRC) (highest skin friction), hydrogel-based FRC without biocides, silylated acrylate self-polishing copolymer coating, and hydrogel-based FRC with biocides (lowest skin friction). However, the differences in skin friction between the latter three coatings were minor and often within the range of experimental uncertainty. The average surface roughness of the FCCs in the newly applied and mechanically cleaned condition, determined as the Rt(50) and R z parameters, was evaluated as poor predictors of skin friction.

Thermodynamic analysis and optimization of a 10 MW OTEC Rankine cycle in Reunion Island with the equivalent Gibbs system method and generic optimization program GenOpt

The ocean thermal energy conversion (OTEC) process uses the difference in temperature between the warm seawater on the ocean surface and the deep cold seawater to operate a Rankine cycle system for producing electrical power without consuming fossil fuel. This thermodynamic cycle uses a very low temperature gradient that limits its efficiency at 3–5%. Consequently every consumptions and losses of the system have to be optimized to increase the cost-effectiveness of this technology. This paper presents a thermodynamic analysis of a closed OTEC Rankine cycle. The model used in this paper is based on the work of Martins, using the concept of equivalent Gibbs systems. In an equivalent system, mass, energy and entropy are linked through the Gibbs equation, and the entropy production can easily be expressed in terms of fluxes and their related forces. Assuming linear phenomenological laws, the phenomenological coefficients are assessed from technical data. This method permits the study or design of a lot of process engineering. Moreover, a reliable analysis of the second principle can be realized, in order to compare several processes. This method will be used to analyze the cycle, to determine which components need to be optimized. Based on these results, sensitivity analysis are made on these components and the generic optimization program GenOpt is used to determine the optimized parameters of a 10MW OTEC plant that could be installed on Reunion Island.

Dual-use open cycle ocean thermal energy conversion (OC-OTEC) using multiple condensers for adjustable power generation and seawater desalination

Multiple condensers are used for dual-use open cycle ocean thermal energy conversion to generate both electric power and desalinated water with preset ratios. Fundamentals of heat and mass transfer phenomena are scrutinized to identify optimal operational conditions of various OC-OTEC plant scales. Important control parameters include warm water temperature and its intake rate, vacuum pressure in the evaporator, and cold water temperature. Intake rate of the cold deep seawater is estimated based on the operational mode and conditions. Performances of the multiple condenser OC-OTEC system, power generation and seawater desalination capacities are analytically evaluated in terms of steam flow fractions, temperature of intake seawater, and vacuum pressure. This research provides unprecedented levels of theoretical depth, mathematical details, and design criteria for highly optimized dual-use OC-OTEC operations. Future research directions for OC-OTEC technologies are also discussed in detail.