Ordinary Sea Water Research Articles

Parametric study, finite element analysis, and load capacity calculation for flexural behaviour of seawater and sea sand concrete beams reinforced with GFRP bars

This study sought to enhance the understanding of seawater sea sand concrete (SWSSC) structures reinforced with glass fiber-reinforced polymer (GFRP) bars. To achieve this, an experimental investigation was conducted involving the production and testing of 6 GFRP bar-reinforced SWSSC beams (GFRP beams) alongside 3 ordinary seawater sea sand concrete (OSWSSC) beams (Ordinary beams) to evaluate their flexural performance. Additionally, a subsequent analysis comprised the establishment of 11 full-scale finite element models aimed at parameter assessment on GFRP beams. The experimental and numerical findings revealed that an increase in sea sand replacement ratio in SWSSC beams, with a shear-span ratio of 2.2, led to varying degrees of shear-compression failure. Notably, owing to the superior crack resistance of SWSSC, the beams demonstrated outstanding structural coordination. Compared to OSWSSC beams, GFRP beams with a 100 % replacement ratio of sea sand or an increased in concrete strength to C55 had initial stiffness values that were 150 % and 106 % larger, respectively. Further investigation unveiled that a reduction in the shear-span ratio from 2.5 to 1.0 or an increase in the longitudinal reinforcement ratio from 1.27 % to 2.53 % significantly augmented the ultimate load-carrying capacity, resulting in increases of 88.0 % and 37.7 %, respectively. Based on these findings, several design recommendations are proposed: 1. Establish a deflection limit at l0/500 or implement more stringent measures for GFRP beams. 2. Consider reducing the diameter of GFRP bars while maintaining a 50 % sea sand replacement rate to mitigate crack formation. 3. An excessive longitudinal reinforcement ratio hampers the enhancement of specimen load-carrying capacity. 4. Consider utilizing Chinese specifications for flexural capacity calculations.

Shrimp Cultured in Low-Salt Saline-Alkali Water has a Better Amino Acid Nutrition and Umami─Comparison of Flavors between Saline-Alkali Water- and Seawater-Cultured Litopenaeus vannamei.

The advantages of Litopenaeus vannamei farming in saline-alkali water have gradually attracted attention, but few studies have focused on its flavor. In this study, L. vannamei cultured in saline-alkali water (SS) and ordinary seawater (CS) (both have a breeding time of 120 days) were selected for analysis (n = 5). High-performance liquid chromatography (HPLC) was used to measure free amino acids and flavoring nucleotides in the muscles of L. vannamei, while the taste activity value (TAV) and equivalent umami concentration (EUC) were used to analyze the degree of umami. The total essential amino acids (TEAA) in the SS group were 238.41 ± 46.24 mg/mL, significantly higher than that in the CS group (107.06 ± 15.65 mg/mL). The total amount of flavor nucleotides in the SS group was 2948.51 ± 233.66 μg/mL, significantly higher than those in the CS group (2530.37 ± 114.67 μg/mL). The content and TAV of some free amino acids (Glu, Cys-s) in the SS group were significantly higher. Meanwhile, due to the significant increase in IMP, the synergistic effect of free amino acids and flavored nucleotides leads to higher EUC. The significant separation of SS and CS samples in principal component analysis (PCA) indicates a significant difference between the two groups. Our results indicate that shrimp cultured in saline-alkali water has a stronger umami. This study enriches the basic theories related to the flavor of salt-alkali water crustaceans.

How Might Plastic Pollution Affect Antarctic Animals?

Antarctica is the least populated place on Earth, but the frozen continent and its surrounding Southern Ocean are still affected by human activities. Scientists have found large pieces of plastic such as fishing nets, and microscopic-sized pieces of plastic, too. Some plastics can be hundreds of times smaller than a grain of sand, and these are called nanoplastics. The Southern Ocean, which surrounds Antarctica, is also warming faster than other oceans and is becoming more acidic. Thus, Antarctic marine animals that have lived in an untouched, stable environment for millions of years are now being exposed to plastic pollution and human-caused climate change. We are studying how Antarctic marine life is coping with plastic pollution in this quickly changing ocean. We focus on Antarctic krill, a small crustacean that supports the Antarctic marine food web. Findings show that krill embryos subjected to ocean acidification and nanoplastics develop less than embryos in ordinary seawater conditions.

Bond-Slip Model of Corrosion-Resistant Rebar and Fiber-Reinforced Seawater Sea-Sand Concrete

Abstract To study the bond performance between fiber-reinforced seawater sea-sand concrete and corrosion-resistant rebars (glass fiber–reinforced polymer [GFRP] bars and epoxy resin–coated rebars) in extremely hot and humid marine environments, bond anchorage tests between reinforcement and seawater sea-sand concrete are conducted to study bond performance. The failure morphology of reinforced concrete was investigated, and the bond-slip curves of different types of rebar and concrete were compared. According to the research results, the addition of basalt and polypropylene fibers to seawater sea-sand concrete changed the distribution of bonding stress, which was conducive to an improvement in the anchorage efficiency of reinforcement and concrete. The chemical bonding performance between the fiber-reinforced seawater sea-sand concrete and rebar is improved, wherein the bond stress increases by 94.01 % at the beginning of the slip, and the residual bond stress increases by 91.72 %. Compared with ordinary seawater sea-sand concrete, the bonding strength between ordinary reinforced rebar and fiber-reinforced seawater sea-sand concrete increased by 20.75 %, and the bonding strength between the GFRP bar and fiber-reinforced concrete decreased by 15.37 %. Based on the friction mechanism of rebars and concrete, bonding strength models of ordinary rebar, epoxy resin–coated rebar, and GFRP bars with fiber-reinforced seawater sea-sand concrete are presented.

Geochemistry of Iron-Manganese Crusts of the Bering Sea

The ferromanganese crusts found in the Bering Sea on the Volcanology Massif, the Alpha Fault Zone, and the Shirshov Submarine Ridge that cover the surface of rocky volcanic structures are most likely the product of post-volcanic activity. The present results indicate that the studied ferromanganese formations were formed under the influence of two factors: on the one hand–as a result of slow precipitation of metals from ordinary seawater, on the other hand–under the possible influence of metal-enriched hydrothermal solutions. In microstructural and mineralogical terms, the composition of Fe–Mn crusts of the Bering Sea turned out to be rather monotonous. The ore part is represented mainly by ferruginous vernadite and rarely hematite in combination with amorphous silica, to a lesser extent montmorillonite, calcite, and aragonite. The manganese mineral todorokite, considered a reliable sign of hydrothermal origin of ore crusts, was not detected in our samples. In the studied samples the reduced cerium anomaly (0.87) was established only in one sample, and in other samples its value varies within 1.08–1.89, which is typical for the upper horizons of the ocean water column. At the same time, the europium anomaly is close to neutral, so in 7 samples its value is 0.96–1.03 (average 1.0) and only in three samples it is slightly increased (1.05–1.07), which can be considered a very weak sign of hydrothermal activity. In addition, the presence of gold microinclusions in the ferromanganese phase can indirectly indicate the possible influence of hydrothermal factor on the crust composition.

Proof and Application of Discriminating Ocean Oil Spills and Seawater Based on Polarization Ratio Using Quad-Polarization Synthetic Aperture Radar

This paper focuses on the proof and application of discriminating between oil spills and seawater (including the “look-alikes”, named low wind areas) based on the polarization ratio. A new relative polarization ratio (PRr) method is proposed, which is based on the difference between the scattering mechanism and the dielectric constant for oil spills compared to that of seawater. The case study found that (1) PRr numerically amplifies the contrast between oil spills and seawater, reduces the difference between low wind areas and ordinary seawater, and exhibits better details of the image; (2) the threshold method based on Euclidean distance can obtain the highest classification overall accuracy within the allowable error range, and can be widely used in the study of different incidence angles and environmental conditions; and (3) the identification of oil spills and seawater by the proposed methods can largely avoid the misjudgment of low wind areas as oil spills. Considering visual interpretation as the reference ‘ground truth’, the overall classification accuracy of all cases is more than 95%; only the edge of the diffuse thin oil slick and oil–water mixture is difficult to identify. This method can serve as an effective supplement to existing oil spill detection methods.

Investigation on mechanical properties improvement of seawater engineered cementitious composites (ECC) using FA/LC2

The purpose of this study was to investigate the effect of polypropylene (PP) fibers and supplementary cementitious materials (SCMs) on the compressive and flexural properties of seawater engineered cementitious composites (ECC). A total of 12 mix ratios and 4 curing ages were designed in the experiment. The SCMs used limestone calcined clay (LC2) and fly ash (FA). The effects of seawater, SCMs and PP fibers on the load carrying capacity, deformation capacity and energy absorption capacity under compression and flexural resistance were explored. The pore structure and micromorphology were investigated by MIP and SEM, respectively. The results show that the incorporation of 25 % LC2 can show better mechanical properties and promote early hydration. At 56 d curing age, its compressive strength and flexural strength can reach 53.27 MPa and 6.30 MPa, respectively. Adding 2 % volume of PP fiber to cement composites can further increase the toughness of the material, especially when combined with 25 % LC2, its compressive and flexural properties are better than those of ordinary seawater ECCs.

Friction and transfer behavior of alumina nanoparticle-reinforced carbon fiber/polyoxymethylene composites in the deep sea environment

Ternary nanocomposites based on carbon fiber (CF)/polyoxymethylene (POM) composites and further reinforced with different amounts of α-phase alumina (Al2O3) nanoparticles were fabricated. The results show that the incorporation of Al2O3 nanoparticles simultaneously enhances mechanical strength, thermal stability and seawater resistance, and optimal properties were obtained at 4.0% Al2O3 nanoparticle loading. Remarkable enhancement of tribological properties in seawater at ordinary pressure was attained, while elevated seawater pressure weakened the wear resistance of Al2O3/CF/POM composites. At ordinary seawater pressure, the tribological properties of Al2O3/CF/POM composites were revealed to be governed by the transfer behavior between polymer-metal interface. At elevated seawater pressures, however, the transfer of Al2O3/CF/POM composites prevents the metallic counterpart from corrosion-wear damage at the expense of increased wear loss.

Determination of Ultratrace Level 135Cs and 135Cs/137Cs Ratio in Small Volume Seawater by Chemical Separation and Thermal Ionization Mass Spectrometry.

The atomic ratio of 135Cs/137Cs is a powerful fingerprint for distinguishing the source terms of radioactive contamination and tracing the circulation of water masses in the ocean. However, the determination of the 135Cs/137Cs ratio is very difficult due to the ultratrace level of 135Cs (<0.02 mBq/m3) and 137Cs (<2 Bq/m3) in the ordinary seawater samples. In this work, a sensitive method was developed for determination of 135Cs concentration and 135Cs/137Cs ratio in seawater using chemical separation combined with thermal ionization mass spectrometry (TIMS) measurement. Cesium was first preconcentrated from seawater using ammonium molybdophosphate-polyacrylonitrile column chromatography and then purified using cation exchange chromatography to remove the interferences. With this method, decontamination factors of 6.0 × 106 for barium and 1800 for rubidium and a chemical yield of more than 60% for cesium were achieved. By using glucose as an activator, the ionization efficiency of cesium was significantly improved to 50.6%, and a constant high current of Cs+ (20 V) can be maintained for more than 180 min, which ensures sensitive and reliable measurement of low level 135Cs and 137Cs. Detection limits of 4.0 × 10-17 g/L for both 135Cs and 137Cs for 200 mL seawater were achieved, which enables the accurate determination of 135Cs concentration and 135Cs/137Cs ratio in a small volume of seawater samples (<200 mL). The developed method has been validated by analysis of seawater reference material IAEA-443. Seawater samples collected from the Greenland Sea, Baltic Sea, and Danish Straits have been successfully analyzed for 135Cs concentrations and 135Cs/137Cs ratios, and the results showed that 135Cs concentrations in the seawater of the Baltic Sea is much higher than that in the Greenland Sea, which is attributed to the high deposition of Chernobyl accident derived radiocesium in the Baltic Sea region.

Mechanisms and experimental research of ion-matched waterflooding to enhance oil recovery in carbonate reservoirs: A case of Cretaceous limestone reservoirs in Halfaya Oilfield, Middle East

Abstract Based on systematically summarizing the achievements of previous ion-matched waterflooding researches, the diversity and synergy of oil recovery enhancement mechanisms and the interaction between mechanisms are examined according to two classification standards, and the influence of behaviors of different ions on different mechanisms and oil displacement efficiency are investigated. Ionic strength is proposed to characterize the behavior differences of univalent and divalent ions, the relationships between ionic strength, effective concentration, and mechanisms are established to characterize the ion behavior behind various mechanisms, and evaluate the performance of ion-matched injection water. The mechanisms of enhancing oil recovery by ion-matched waterflooding include: (1) The ion-matched water can reduce the ion strength and match the ion composition of formation water, thereby reducing the difference between the effective concentration of univalent ions and divalent ions on the surface of carbonate rocks, and improving the effective concentration of potential determining ions (especially SO42—). (2) It can improve wettability, oil-water interface properties, pore structure and physical properties of the reservoir, and finally enable the establishment of a new ionic equilibrium conducive to waterflooding while breaking the original equilibrium. In this study, experiments such as relative permeability curve, interfacial tension, and core-flooding were carried out on carbonate core samples from the Cretaceous Mishrif Formation reservoirs in Halfaya Oilfield, Middle East, a method for injection water evaluation was established and the injection water suitable for these reservoirs was selected: 6 times diluted seawater. Compared with ordinary seawater, oil displacement efficiency can be increased by more than 4.60% and compared with the optimum dilution of formation water, oil displacement efficiency can be increased by 3.14%.

Sequential carbonate mineralization of desalination brine for CO2 emission reduction

Desalination brine is a potential source for CO2 mineralization aimed at reducing CO2 emissions, because the concentration of Ca and Mg in brine is almost twice that of ordinary seawater. However, the previously achieved conversion ratio of CO2 to carbonate minerals is too low for commercial application, as Ca and Mg compete and interfere with each other during precipitation. In this study, we tested the separate and sequential mineralization of Ca and Mg in brine, enhancing the CO2 conversion ratio to 57% from 12%. We also tested the use of 15% CO2 gas (the typical concentration of actual combustion gas), and it was observed that 69% of injected CO2 was precipitated as Ca and Mg carbonate minerals and 99% of Ca and 69% of Mg in the initial brine were precipitated. In addition, the volume of NaOH solution required was reduced by 76%. This revised method is more material- and reagent-efficient which would likely have lower operation costs; moreover, as no further additives are required, environmental impact of brine release is also likely to be reduced. The findings of this study can help address environmental problems caused by large seawater desalination plants and thermal power plants.

Effect of salinity and ion type on formation damage due to inorganic scale deposition and introducing optimum salinity

Abstract Smart water injection is recognized as an effective EOR process to alter the wettability and interfacial tension to obtain higher micro/macro sweep efficiencies. This water contains reactive ions such as Mg 2 + , Ca 2 + and SO 4 2 - which can act as potential-determining ions and change the surface charge of calcite rocks. One of the major concerns in the execution of an effective water-flood process, especially in tight carbonate reservoirs, is the chemical incompatibility between the formation brine and the injecting water. In the present study, laboratory fluid compatibility tests were carried out and software simulation was done to investigate the most important challenges of the water-flooding process in one of the West Iranian oil fields with the possibility of developing formation damage. The chemical incompatibility between injected smart water and formation water leads to inorganic scale deposition. For this purpose, sea water as the basis of smart water was prepared to examine the impact of determining ions such as Mg 2 + , Ca 2 + , and SO 4 2 - and, to examine the effect of the salinity of the injected brine on the total amount of CaSO 4 scale precipitation. According to the obtained results, as the concentration of SO 4 2 - in the injecting sea water increases from 1 / 4 to 1 times its concentration in ordinary sea water, the CaSO 4 precipitation increases smoothly, and then it is accelerated as the concentration increases beyond that. Therefore, even though the increasing of the sulfate concentration improved the wettability alteration ability of the smart water, calcium sulfate deposition was noticed, resulting in permanent formation damage. The test results also showed that CaSO 4 deposition increases as the concentration of Ca 2 + in the sea water increases. On the other hand, the presence of Mg 2 + ion in sea water increases the solubility of CaSO 4 and subsequently, lower scale formation was noticed by increasing the concentration of magnesium. This study also showed that there is an optimum salinity in which the minimum amount of mineral scale is deposited, and 5 times dilution of sea water is determined as the optimum salinity. The findings would enable us to optimize the ion contents of smart water for both, better oil sweep efficiency and lower risk of formation damage. In the end, this paper discusses the laboratory fluid compatibility results and scale prediction analysis for different smart water injection utilizations.

Modified seawater as a smart EOR fluid in chalk

Abstract Water based EOR by wettability alteration is of interest among the oil companies because of economic and environmental reasons. It is well known that seawater acts as a wettability modifier in carbonate reservoirs, and the seawater can even be improved as a smart EOR fluid by removing Na + and Cl − ions, and spiking this NaCl-depleted seawater with SO 4 2 - ions. In this paper we have addressed the degree of seawater modification needed to achieve reasonable improvements in oil recovery in spontaneous imbibition processes at 90 °C. Compared to ordinary seawater as imbibing fluid, more than 90% of the NaCl content must be removed in order to increase the oil recovery by 7–8% OOIP. Furthermore, compared to seawater depleted in NaCl, the oil recovery could be increased by 10% OOIP by spiking the NaCl depleted seawater with sulfate, 3–4 times the sulfate concentration present in seawater. The increased efficiency of modified seawater as a smart EOR fluid in carbonate is discussed in terms of a decrease in the ionic density of the double layer close to the positively charged calcite surface.

Crystal Growth of Clathrate Hydrate at the Interface between Seawater and Hydrophobic-Guest Liquid: Effect of Elevated Salt Concentration

This paper reports the visual observations of the clathrate hydrate crystal growth and morphology at the interface of aqueous NaCl solutions and a guest-substance liquid. The hydrate crystal growth was visually characterized in the systems of a wide range of NaCl concentrations from 0.035 to 0.264 in mass fraction. The mass fraction 0.035 was corresponding to that of ordinary seawater, and the salt concentration tested was extended up to the saturation level, i.e., 0.264. Cyclopentane was used as the guest substance. Formation and growth of hydrate crystals at the cyclopentane-NaCl solution interface were observed. We visually analyzed the individual hydrate crystals and classified the morphology of the crystals according to ΔTsub at atmospheric pressure. It was found that the size of the individual hydrate crystals decreased with increasing ΔTsub. The results showed that the morphology of the individual hydrate crystals in any NaCl concentration is roughly similar at a given ΔTsub. We also measured the l...

Mechanical Constraint Converts Planar Waves into Helices on Tunicate and Sea Urchin Sperm Flagella

The change in the flagellar waves of spermatozoa from a tunicate and sea urchins was examined using high-speed video microscopy to clarify the regulation of localized sliding between doublet microtubules in the axoneme. When the tunicate Ciona spermatozoa attached to a coverslip surface by their heads in seawater or they moved in seawater with increased viscosity, the planar waves of the sperm flagella were converted into left-handed helical waves. On the other hand, conversion of the planar waves into helical waves in the sea urchin Hemicentrotus spermatozoa was not seen in seawater with an increased viscosity as well as in ordinary seawater. However, the sea urchin Clypeaster spermatozoa showed the conversion, albeit infrequently, when they thrust their heads into seawater with an increased viscosity. The chirality of the helical waves of the Clypeaster spermatozoa was right-handed. When Ciona spermatozoa swam freely near a glass surface, they moved in relatively large circular paths (yawing motion). There was no difference in the proportion of spermatozoa yawing in either a clockwise or counterclockwise direction when viewed from above, which was also different from that of the sea urchin spermatozoa. These observations suggest that the planar waves generally observed on the sperm flagella are mechanically regulated, although their stability must depend on the Ca(2+) concentration in the cell. Furthermore, the chirality of the helical waves may be determined by the intracellular Ca(2+) concentration and changed by transmitting the localized active sliding between the doublet microtubules around the axoneme in an alternative direction.

The brine shrimp artemia: adapted to critical life conditions.

The brine shrimp Artemia is a micro-crustacean, well adapted to the harsh conditions that severely hypersaline environments impose on survival and reproduction. Adaptation to these conditions has taken place at different functional levels or domains, from the individual (molecular-cellular-physiological) to the population level. Such conditions are experienced by very few equivalent macro-planktonic organisms; thus, Artemia can be considered a model animal extremophile offering a unique suite of adaptations that are the focus of this review. The most obvious is a highly efficient osmoregulation system to withstand up to 10 times the salt concentration of ordinary seawater. Under extremely critical environmental conditions, for example when seasonal lakes dry-out, Artemia takes refuge by producing a highly resistant encysted gastrula embryo (cyst) capable of severe dehydration enabling an escape from population extinction. Cysts can be viewed as gene banks that store a genetic memory of historical population conditions. Their occurrence is due to the evolved ability of females to “perceive” forthcoming unstable environmental conditions expressed by their ability to switch reproductive mode, producing either cysts (oviparity) when environmental conditions become deleterious or free-swimming nauplii (ovoviviparity) that are able to maintain the population under suitable conditions. At the population level the trend is for conspecific populations to be fragmented into locally adapted populations, whereas species are restricted to salty lakes in particular regions (regional endemism). The Artemia model depicts adaptation as a complex response to critical life conditions, integrating and refining past and present experiences at all levels of organization. Although we consider an invertebrate restricted to a unique environment, the processes to be discussed are of general biological interest. Finally, we highlight the benefits of understanding the stress response of Artemia for the well-being of human populations.

Tensile Properties of GFRP Bars after Exposure to Harsh Laboratory and Field Environmental Conditions

This paper presents the test results of an experimental study that investigates the durability of a new generation of Glass Fiber Reinforced Polymer (GFRP) bars. A total of 60 GFRP bars were embedded in concrete prisms and exposed to ten environmental conditions for 6 and 12 months. The environments included exposure to ordinary tap water, sea water, and alkaline solution at two temperatures (room and 50°C). The environments also included two typical field conditions of the Kingdom of Saudi Arabia (Gulf area and Riyadh area). The performance of the GFRP bars was evaluated by conducting tensile tests on the bars extracted out of the concrete specimens after exposure to the environmental conditions. After 12 months of exposure, the test results showed that the tap water at 50°C had the maximum effect on the tensile strength of the GFRP bars. The two field conditions did not show any harmful effect on the tensile properties of the bars after 12 months of exposure.

“Smart Water” as a Wettability Modifier in Chalk: The Effect of Salinity and Ionic Composition

Seawater can improve the water wetness of chalk at high temperatures, which improves the oil displacement by spontaneous imbibition of water. It is experimentally verified that the interaction between Ca2+, Mg2+, and SO42− at the chalk surface will displace adsorbed carboxylic acids and increase the water wetness. In this work, the effect of salinity and ionic composition of smart water on oil recovery was studied at different temperatures, 100, 110, and 120 °C. The ultimate oil recovery was compared using seawater as the base fluid. When NaCl was removed from seawater, both the imbibition rate and oil recovery increased in comparison to seawater at the temperatures tested. At 110 and 120 °C, the oil recovery from seawater depleted in NaCl increased by about 10% of original oil in place (OOIP) compared to seawater. A decrease in oil recovery of about 5% of OOIP was observed when increasing the amount of NaCl in seawater 4 times. A systematic decrease in oil recovery was observed when using seawater diluted with distilled water as imbibing fluid. Imbibition tests at 110 °C showed that the water-wet fraction increased 29% for seawater depleted in NaCl compared to 11% for ordinary seawater. Diluted seawater to 10 000 ppm did not change wetting conditions at 110 °C. The results confirmed that not only is the concentration of the active ions Ca2+, Mg2+, and SO42− important for wettability alteration to take place but also the amount of non-active salt, such as NaCl, has an impact on the wettability alteration process, which is discussed as a double-layer effect at the chalk surface. No significant improvement in the ultimate oil recovery was observed during forced displacement by modified seawater.

Semiconductor gel in shark sense organs?

Sharks can sense bioelectric fields of prey and other animals in seawater using an extraordinary system of sense organs (ampullae of Lorenzini) [R.D. Fields, The shark's electric sense. Sci. Am. 297 (2007) 74-81]. A recent study reported that these sense organs also enable sharks to locate prey-rich thermal fronts using a novel mode of temperature reception without ion channels. The study reported that gel extracted from the organs operates as a thermoelectric semiconductor, generating electricity when it is heated or cooled [B.R. Brown, Neurophysiology: sensing temperature without ion channels, Nature 421 (2003) 495]. Here we report biophysical studies that call into question this mechanism of sensory transduction. Our experiments indicate that the material exhibits no unusual thermoelectric or electromechanical properties, and that the thermoelectric response is an artifact caused by temperature effects on the measurement electrodes. No response is seen when non-metallic electrodes (carbon or salt bridges) are used, and ordinary seawater produces the same effect as shark organ gel when silver wire electrodes are used. These data are consistent with the voltages arising from electrochemical electrode potentials rather generated intrinsically within the sample. This new evidence, together with the anatomy of the organs and behavioral studies in the literature, best support the conclusion that the biological function of these sense organs is to detect electric fields.

Silurian bryozoans from Gotland fossilized in galena and sphalerite

Marls and limestones from the Lower Visby Marl of Gotland, close to the Llandovery/Wenlock boundary, contain rare specimens of bryozoans fossilized in galena or sphalerite. One species (possibly two) are mineralized by galena, and one by sphalerite out of about 20 bryozoan species (and many more species from other animal groups) in the same rock. The mechanisms of mineralization seem to occur in several stages, possibly involving microbial activity. The lead content of the sediment also seems to be extremely high. These observations raise taphonomic, palaeontological, sedimentological and geochemical problems, which are discussed: 1) the origin of the lead (ordinary sea water?), 2) origin of the high metal (especially lead) content of the rock (accumulation through green algae?), 3) the mechanism of mineralization through replacement of the bryozoan skeletal calcite (involving changes in pH, and other processes in the pore water?) and 4) why galena was only deposited on one (or two) species and sphalerite in another (nucleation initiated by microbes on species specific matrix proteins?).