Conductivity Of Seawater Research Articles

Exploring model space via 1D extremal inversion of airborne TEM data: determination of depth and conductivity bounds of seawater and sediment in shallow coastal waters

The aim of extremal inversion is to construct models with maximal or minimal characteristics, but which nonetheless fit the observed data acceptably well. Given one model which fits the data, extremal inversion enables the user to explore the permissible range of model parameters, hence determine parameter uncertainty. A 1D extremal inversion algorithm has been developed for horizontal loop TEM. Extremal inversion is effected via linear programming. The objective is maximisation or minimisation of a particular layer conductivity or depth. Bounds (on conductivity or depth) can be imposed explicitly as inequality constraints. Extremal models can differ markedly from the first model which fits the data. Extremal inversion is non-linear and is not confined to a neighbourhood which is 'linearly close' to the first model. As an example of the application of this method, 1D extremal inversion is applied to airborne TEM data acquired over shallow seawater to determine upper and lower bounds on depths of seawater and bedrock and on conductivities of seawater and marine sediment. The results compare favourably with available ground truth data. Estimates of parameter uncertainty derived from extremal inversion are as follows: ±0.6 S/m for seawater conductivity, ±0.2 S/m for sediment conductivity, ±0.7 m for seawater depth, and ±8 m for bedrock depth.

Long-term investigation of fouling of cation and anion exchange membranes in microbial desalination cells

The fouling of ion exchange membranes in microbial desalination cells (MDCs) was investigated through an eight-month operation. Multiple MDCs were set up by using cation (CEM), anion (AEM), and/or proton (Nafion) membranes. The MDCs exhibited relatively constant reduction of conductivity of artificial seawater during the testing period (46.3±6.3% in the CEM-MDC and 78.7±0.8% in the Nafion-MDC in an operating cycle). However, the current generation decreased from 99 to 56A/m3 in the CEM-MDC after 250days, and from 97 to 46A/m3 in the Nafion-MDC after 130days, indicating the presence of membrane fouling. Theoretically the MDCs removed 6.7–12.1kgTDS/m3/d with a high charge transfer efficiency of 230–440%, suggesting that electric current was not the only factor to drive desalination; water dilution played an important role in conductivity reduction as well. It was observed that the AEM contained significant biofouling, resulting from wastewater and microbial growth on organic compounds migrating across the membrane, while the CEM had substantial inorganic scaling, mainly consisting of calcium and magnesium. The membrane resistance of the CEM increased more significantly than that of the AEM, indicating that CEM needs more maintenance during MDC operation.

Review paper: Instrumentation for marine magnetotelluric and controlled source electromagnetic sounding

ABSTRACTWe review and describe the electromagnetic transmitters and receivers used to carry out magnetotelluric and controlled source soundings in the marine environment. Academic studies using marine electromagnetic methods started in the 1970s but during the last decade these methods have been used extensively by the offshore hydrocarbon exploration industry. The principal sensors (magnetometers and non‐polarizing electrodes) are similar to those used on land but magnetotelluric field strengths are not only much smaller on the deep sea‐floor but also fall off more rapidly with increasing frequency. As a result, magnetotelluric signals approach the noise floor of electric field and induction coil sensors (0.1 nV/m and 0.1 pT) at around 1 Hz in typical continental shelf environments. Fluxgate magnetometers have higher noise than induction coils at periods shorter than 500 s but can still be used to collect sea‐floor magnetotelluric data down to 40–100 s. Controlled source transmitters using electric dipoles can be towed continuously through the seawater or on the sea‐bed, achieving output currents of 1000 A or more, limited by the conductivity of seawater and the power that can be transmitted down the cables used to tow the devices behind a ship. The maximum source‐receiver separation achieved in controlled source soundings depends on both the transmitter dipole moment and on the receiver noise floor and is typically around 10 km in continental shelf exploration environments. The position of both receivers and transmitters needs to be navigated using either long baseline or short baseline acoustic ranging, while sea‐floor receivers need additional measurements of orientations from compasses and tiltmeters. All equipment has to be packaged to accommodate the high pressure (up to 40 MPa) and corrosive properties of seawater. Usually receiver instruments are self‐contained, battery powered and have highly accurate clocks for timekeeping, even when towed on the sea‐floor or in the water column behind a transmitter.

New correlations for seawater and pure water thermal conductivity at different temperatures and salinities

The thermal conductivity of natural seawater is measured at atmospheric pressure, temperature range of 10–90°C, and salinity range of 0–120g/kg. Samples of natural seawater is collected from the Arabian Gulf and prepared for different salinities by evaporation and dilution techniques. The experimental apparatus used in the measurements is a modified comparative radial-heat-flow concentric-cylinder apparatus that uses a steady state measurement technique. The method gives the ratio of the thermal conductivity of pure water to that of seawater. A simple correlation for the pure water thermal conductivity is developed based on the model provided by The International Association for the Properties of Water and Steam (IAPWS 2011) and has a maximum deviation of 0.05%. A simple model for the thermal conductivity ratio of pure water to seawater is developed and compared with the measured data, data in the literature, and a recent theoretical model for mixed-solvent electrolyte solutions. The maximum deviation between the present model prediction and the measurement is ±1% while the maximum deviation from the recent theoretical model is found to be 0.5%.

Transient marine electromagnetic responses of 3D resistive structures: Implications for navigation

The marine controlled-source electromagnetic method has become a popular technique for mapping the electrical resistivity structure of the seafloor. Electromagnetic fields, produced by an electric dipole transmitter, diffuse through the earth and are recorded on the seabed by nodal or cable based electric dipole receivers. Accurate information on transmitter and receiver geometry is extremely important for proper interpretation; errors in the position and orientation of the transmitter and/or the receivers propagate into errors in the predicted seafloor resistivity. We consider the special situation where a receiver cable is towed in the vicinity of a transmitter which is located on the seafloor with a known position and orientation. We theoretically and numerically examine the response of this system for a selection of 1D, 2D, and 3D models, and show that although the electromagnetic field recorded at early times contains information about the subsurface resistivity, the late time decay of the transient response is only a function of the seawater conductivity and receiver position for all the models we consider. In fact, the shape of the late time decay is almost exactly the same as that of a dipole in a wholespace having the same resistivity as seawater. This shows that late time transient information can be used to determine the position of the receiver cable, whereas early time information can be used to determine the resistivity structure of the seafloor.

Airborne electromagnetic bathymetry and estimation of bedrock topography in Broken Bay, Australia

A helicopter transient electromagnetic (TEM) survey was flown over shallow coastal waters in Broken Bay, Australia, overlying several palaeovalleys and exposed reef sections. The infilled palaeovalleys contain unconsolidated sediments with variable thicknesses exceeding 100 m. Previous marine seismic reflection and vibrocore studies provide an estimate of sediment thickness and surficial sediment conductivity, respectively, which, combined with known bathymetry (sonar soundings) and measured seawater conductivity, can be used to generate a crude 1D geoelectric ground-truth model consisting of two layers (seawater/sediment) overlying a relatively resistive basement. The primary focus was to examine the accuracy of interpreted water depths obtained by 1D inversion of airborne TEM data, assuming a two-layer over resistive basement model, by comparing these depths with known water depths. The secondary focus was to compare the interpreted sediment thickness (i.e., the thickness of the second geoelectric layer, which combined with bathymetry, gives the bedrock depth) with thicknesses estimated from marine seismic data to test the potential of using airborne electromagnetic systems for remote sensing of the coarse features of the bedrock topography. Interpreted water depths obtained from TEM data resulted in absolute water depth accuracies of 1–2 m for depths between 10 and 30 m, and 0.3–0.5 m in water shallower than [Formula: see text]. More importantly, similar water depth accuracies were obtained using raw TEM data (with birdswing removal) and TEM data obtained by postprocessing using time-consuming empirical corrections based on the TEM half-space response over deep sea water. The interpreted sediment depths derived from TEM and marine seismic data showed good agreement, generally, for example, inversion of TEM data delineated a distinct palaeovalley that transects a beach, with a maximum depth of 60–70 m below the seafloor, in agreement with depths estimated from marine seismic data to within [Formula: see text].

The electrical conductivity of seawater at high temperatures and salinities

Recently a new international standard for the thermodynamic properties of seawater, the Thermodynamical Equation of Seawater—2010 (TEOS-10), has been developed. For some properties it is valid at the high temperatures and salinities that may be found in industrial and desalination processes. However, precise in situ estimates of mass fraction salinities, derived from measurements of electrical conductivity in TEOS-10 using a modification of the Practical Salinity Scale 1978 (PSS-78), have been validated only when temperatures are less than 35°C and salinities are less than 42g/kg. The algorithm has not been validated at higher temperatures and salinities. Here a combination of numerical modeling and measurements is used to determine the electrical conductivity of high salinity and high temperature seawater. It is found that the TEOS-10 salinity algorithm can be used without other corrections to estimate seawater salinities from electrical conductivity for all temperatures between freezing and boiling and all salinities up to the point of calcite precipitation with an accuracy of 1% to 2% or better.

Modeling Thermal Conductivity of Electrolyte Mixtures in Wide Temperature and Pressure Ranges: Seawater and Its Main Components

A model has been established for calculating the thermal conductivity of aqueous electrolyte solutions containing the Na+, K+, Mg2+, Ca2+, Cl−, SO42−, CO32−, HCO3−, and Br− ions. The model is based on a previously developed computational framework for the thermal conductivity of mixed-solvent electrolyte systems, which has been expanded by explicitly accounting for pressure effects in addition to temperature and electrolyte composition effects. The model consists of a contribution of the solvent, a contribution of individual species expressed using modified Riedel coefficients, and an ionic strength-dependent term that is due to interactions between species. The model accurately represents the thermal conductivity of solutions containing single and multiple salts at temperatures ranging from 273 K to 573 K, pressures up to at least 1400 bar, and concentrations up to the limit of solid saturation. Further, the model has been applied to seawater and used to elucidate the discrepancies between the experimental data for seawater and those for Na–K–Mg–Ca–Cl–SO4 salt solutions. With parameters evaluated on the basis of data for binary and multicomponent salt solutions, the model provides reliable predictions of the thermal conductivity of seawater.

Airborne electromagnetic bathymetry investigations in Port Lincoln, South Australia – comparison with an equivalent floating transient electromagnetic system

Helicopter time-domain airborne electromagnetic (AEM) methodology is being investigated as a reconnaissance technique for bathymetric mapping in shallow coastal waters, especially in areas affected by water turbidity where light detection and ranging (LIDAR) and hyperspectral techniques may be limited. Previous studies in Port Lincoln, South Australia, used a floating AEM time-domain system to provide an upper limit to the expected bathymetric accuracy based on current technology for AEM systems. The survey lines traced by the towed floating system were also flown with an airborne system using the same transmitter and receiver electronic instrumentation, on two separate occasions. On the second occasion, significant improvements had been made to the instrumentation to reduce the system self-response at early times. A comparison of the interpreted water depths obtained from the airborne and floating systems is presented, showing the degradation in bathymetric accuracy obtained from the airborne data. An empirical data correction method based on modelled and observed EM responses over deep seawater (i.e. a quasi half-space response) at varying survey altitudes, combined with known seawater conductivity measured during the survey, can lead to significant improvements in interpreted water depths and serves as a useful method for checking system calibration. Another empirical data correction method based on observed and modelled EM responses in shallow water was shown to lead to similar improvements in interpreted water depths; however, this procedure is notably inferior to the quasi half-space response because more parameters need to be assumed in order to compute the modelled EM response. A comparison between the results of the two airborne surveys in Port Lincoln shows that uncorrected data obtained from the second airborne survey gives good agreement with known water depths without the need to apply any empirical corrections to the data. This result significantly decreases the data-processing time thereby enabling the AEM method to serve as a rapid reconnaissance technique for bathymetric mapping.

The practical application of 2D inversion to marine controlled-source electromagnetic data

An algorithm is presented for the inversion of marine controlled-source electromagnetic (CSEM) data that uses a 2D finite difference (FD) forward driver. This code is demonstrated by inverting a CSEM data set collected at Hydrate Ridge, Oregon, consisting of 25 seafloor sites recording a [Formula: see text] transmission frequency. The sites are located across a bathymetric high, with variations in water depth of [Formula: see text] along the [Formula: see text] profile. To model this complex seafloor bathymetry accurately, the FD grid was designed by careful benchmarking using a different 2D finite element (FE) forward code. A comparison of the FE and FD forward model solutions verifies that no features in the inversion are due to inaccuracies of the FD grid. The inversion includes the local seawater conductivity–depth profile as recorded by the transmitter’s conductivity–temperature-depth gauge, because seawater conductivity is known to have a significant effect on the CSEM responses. An apparent resistivity pseudosection of the CSEM data resembles the 2D inversion in general appearance. However, the inversion provides depth and geometric control of features that cannot be provided by the pseudosection and eliminates artifacts generated from the pseudosection projection.

Testing the limits of AEM bathymetry with a floating TEM system

A floating transient electromagnetic (TEM) system (“sea ring”) simulating a low-altitude helicopter airborne electromagnetic (AEM) system was constructed to test the accuracy of the AEM method for measuring water depth and estimating sediment thickness in shallow coastal waters. A square transmitter loop [Formula: see text], plus concentric inner and outer receiver loops, was strung from masts supported by the circular sea-ring base. Data were stacked over periods from 1 to approximately [Formula: see text] and with loop heights ranging between approximately 5.5 and [Formula: see text] above sea level. The towed sea ring provides a stable platform at a known fixed altitude in calm waters. We have undertaken modeling to investigate the effect of vertical and horizontal displacements of the loops, and to compare circular and square loopgeometries, in proximity to the sea surface. With relatively long stacking times, as long as approximately [Formula: see text], the uncertainty in altitude can be reduced to very low levels. The sea ring has been deployed near Port Lincoln, Australia, in an area with known bathymetry, seawater conductivity [Formula: see text], and sediment thickness (from marine seismic). Initial 1D inversion of raw sea-ring data highlighted significant instrument calibration errors. Empirical correction factors were defined to achieve agreement between measured and modeled TEM responses at selected control points. These corrections were then applied to the entire data set. The 1D inversion of corrected sea-ring data predicted seawater depths within approximately [Formula: see text] of known depths down to [Formula: see text]. These results provide an upper limit to the accuracy that can be expected from airborne EM systems for shallow bathymetry using current technology.

Electrical conductivity of seawater during ohmic heating

The aim of this study was to apply ohmic heating method to generate heat in seawater as an attempt to be utilized in desalination process as an alternative heating method rather than using steam boilers. The effects of temperature, electrical field strength and the concentrations of total dissolved solids (TDS) on electrical conductivity during ohmic heating of seawater were investigated. Heat was generated within the seawater using alternating electric current at frequency of 60 Hz, the range of electrical field strength was 6.35–11.04 (V/cm). Different concentrations of the seawater were prepared (range 38.9–106.1 PPT). Quality parameters include electrical conductivity, colour, pH, apparent specific heat and density of the seawater were measured at room temperature before and after the ohmic heating. The range of conductivity during ohmic heating was 55–399.6 (mS/cm) and strongly dependent on TDS and temperature. Ohmic heating can be applied for heating process of seawater with some limitations regarding the colour change. One major output of this research is the assessment of seawater electrical conductivity data during ohmic heating which adds a new perspective to system analysis, design and modeling of the potential use of ohmic heating to generate heat within the seawater during desalination process.

Caprellids (Crustacea: Amphipoda) associated with the intertidal alga Corallina elongata along the Iberian Peninsula

Abundance patterns of intertidal caprellids associated with the alga Corallina elongata were studied along the Iberian Peninsula. Nineteen stations were selected. The Mediterranean coast showed higher seawater temperature and conductivity and lower dissolved oxygen and turbidity than the Atlantic coast. Cover of C. elongata was negatively correlated with seawater temperature and decreased towards the Mediterranean sites. Number of caprellid species and abundances were higher in stations in the Strait of Gibraltar, probably related with the currents' dynamic around this area. In general, caprellids associated with C. elongata were more abundant along the Mediterranean than along the Atlantic, in spite of the lower algal cover in Mediterranean stations. Caprella hirsuta and C. liparotensis were restricted to the Mediterranean coast whereas C. penantis was only found in the Atlantic and the Strait of Gibraltar. Although C. grandimana has been reported along the Mediterranean, its presence on Corallina elongata was restricted to the Strait of Gibraltar. Oppositely, Caprella liparotensis, which usually inhabits Atlantic and Mediterranean intertidal ecosystems, was only present in the Mediterranean and did not coexist with C. penantis along the Atlantic. Probably, competence process among C. grandimana, C. hirsuta, C. liparotensis and C. penantis are regulating the distribution patterns on the intertidal alga Corallina elongata. On the other hand, canonical correspondence analysis showed a clear preference of Caprella penantis at sites with high oxygen concentrations, whereas C. hirsuta was mainly influenced by higher temperature and conductivity.

A model for predicting changes in the electrical conductivity, practical salinity, and absolute salinity of seawater due to variations in relative chemical composition

Abstract. Salinity determination in seawater has been carried out for almost 30 years using the Practical Salinity Scale 1978. However, the numerical value of so-called practical salinity, computed from electrical conductivity, differs slightly from the true or absolute salinity, defined as the mass of dissolved solids per unit mass of seawater. The difference arises because more recent knowledge about the composition of seawater is not reflected in the definition of practical salinity, which was chosen to maintain historical continuity with previous measures, and because of spatial and temporal variations in the relative composition of seawater. Accounting for these spatial variations in density calculations requires the calculation of a correction factor δSA, which is known to range from 0 to 0.03 g kg−1 in the world oceans. Here a mathematical model relating compositional perturbations to δSA is developed, by combining a chemical model for the composition of seawater with a mathematical model for predicting the conductivity of multi-component aqueous solutions. Model calculations for this estimate of δSA, denoted δSRsoln, generally agree with estimates of δSA based on fits to direct density measurements, denoted δSRdens, and show that biogeochemical perturbations affect conductivity only weakly. However, small systematic differences between model and density-based estimates remain. These may arise for several reasons, including uncertainty about the biogeochemical processes involved in the increase in Total Alkalinity in the North Pacific, uncertainty in the carbon content of IAPSO standard seawater, and uncertainty about the haline contraction coefficient for the constituents involved in biogeochemical processes. This model may then be important in constraining these processes, as well as in future efforts to improve parameterizations for δSA.

Distributional and ecological patterns of caprellids (Crustacea: Amphipoda) associated with the seaweed Stypocaulon scoparium in the Iberian Peninsula

The distribution and abundance patterns of the caprellids (Crustacea: Amphipoda) associated with the alga Stypocaulon scoparium (L.) Kutzing were studied on a spatial scale along the Iberian Peninsula. Fourteen stations and five environmental factors were considered (seawater temperature, conductivity, dissolved oxygen, turbidity and pH). The Atlantic coast was characterized by lower temperature and conductivity as well as higher values of oxygen and turbidity than the Mediterranean coast, probably associated with a higher swell. Cover of S. scoparium was higher in the Strait of Gibraltar than in the remaining stations, coinciding with maximum values of number of caprellid species and Shannon diversity, while abundances were higher in the Mediterranean. Caprella acanthifera and C. liparotensis were dominant at the stations of the Strait of Gibraltar, C. penantis and C. danilevskii were restricted to Atlantic stations, while C. grandimana and C. hirsuta were very abundant in all the Mediterranean stations; Deutella schieckei, C. acanthifera discrepans, Phtisica marina and Pseudoprotella phasma, were only found at some Mediterranean sites. Multivariate analysis showed that some species, such as C. penantis, significantly correlated with oxygen concentrations, while other species, such as P. phasma, D. schieckei and Phtisica marina were associated with stations with higher values of conductivity, temperature and turbidity. Number of caprellids associated with S. scoparium was significantly higher than in other dominant algae from the Mediterranean and the Atlantic, probably due to the optimal morphological structure of this seaweed for caprellids to cling.

Underwater wireless communication system

Underwater communication has a range of applications including remotely operated vehicle (ROV) and autonomous underwater vehicle (AUV) communication and docking in the offshore industry. Current underwater transmission techniques is primarily utilise sound waves for large distance at lower frequencies and the velocity of sound in water is approximately 1500m/s the resultant communications have problems with multi-path propagation and low bandwidth problems. The use of electromagnetic (EM) techniques underwater has largely been overlooked because of the attenuation due to the conductivity of seawater. However, for short range applications, the higher frequencies and much higher velocity can prove advantageous. This paper will outline a project which will utilise recent investigations that demonstrate EM wave propagation up to the MHz frequency range is possible in seawater.

The feasibility of reservoir monitoring using time-lapse marine CSEM

Monitoring changes in hydrocarbon reservoir geometry and pore-fluid properties that occur during production is a critical part of estimating extraction efficiency and quantifying remaining reserves. We examine the applicability of the marine controlled-source electromagnetic (CSEM) method to the reservoir-monitoring problem by analyzing representative 2D models. These studies show that CSEM responses exhibit small but measureable changes that are characteristic of reservoir-depletion geometry, with lateral flooding producing a concave-up depletion-anomaly curve and bottom flooding producing a concave-down depletion-anomaly curve. Lateral flooding is also revealed by the spatial-temporal variation of the CSEM anomaly, where the edge of the response anomaly closely tracks the retreating edge of the flooding reservoir. Measureable changes in CSEM responses are observed when 10% of the resistive reservoir is replaced by conductive pore fluids. However, to avoid corrupting the relatively small signal changes associated with depletion, the acquisition geometry must be maintained to a fraction of a percent accuracy. Additional factors, such as unknown nearby seafloor inhomogeneities and variable seawater conductivity, can mask depletion anomalies if not accounted for during repeat monitoring measurements. Although addressing these factors may be challenging using current exploration CSEM practices, straightforward solutions such as permanent monuments for seafloor receivers and transmitters are available and suggest the method could be utilized with present-day technology.

Development of a helicopter time domain system for bathymetric mapping and seafloor characterisation in shallow water

Time domain airborne electromagnetic (AEM) data acquired from surveys over seawater in Australian coastal waters can be interpreted to obtain seawater depths (Vrbancich and Fullagar, 2007a; Wolfgram and Vrbancich, 2007; Vrbancich, 2009) and to identify the coarse features of bedrock topography (Vrbancich and Fullagar, 2007b; Vrbancich, 2009). A comparison of derived water depths in shallow areas (< 50 m) with known bathymetry has shown that sub-metre depth accuracies can be achieved but these accuracies are not maintained over the entire survey region. Furthermore, the quantitative interpretation of AEM data using 1D inversion methods may require data rescaling (Vrbancich and Fullagar, 2007a; Vrbancich, 2009) and the measured seawater conductivity as a known parameter. The rescaling coefficients in these studies were obtained from the slope and intercept of linear fits between modelled and observed decays at representative sites (control points) with known water depths. These restrictions limit the potential of AEM for accurate bathymetric mapping. A time domain helicopter AEM system (SeaTEM) is currently being developed for the Defence Science and Technology Organisation for shallow water bathymetric mapping. This system consists of a transmitter and receiver loop assembly mounted on a rigid structure referred to as a ?bird? that is towed as a sling load below the helicopter. Instrument stability, calibration (Vrbancich and Fullagar, 2007a; Brodie and Sambridge, 2006; Davis and Macnae, 2008) and the ability to accurately track both the swaying motion (i.e. bird swing) and the altitude of the AEM sensor system over seawater during survey (Davis et al., 2006; Kratzer and Vrbancich, 2007) are issues that need to be addressed in order to develop AEM as a reliable and accurate bathymetry mapping technique. System calibration, self-response, transmitter current waveform, and altimetry were investigated and preliminary findings are reported in this paper.

Distribution of iron in the surface and groundwaters of East Godavari district, Andhra Pradesh, India

With the progradation of Godavari delta in the east coast of India, increase in iron (Fe) concentrations in the groundwater was observed. High concentrations of Fe (>10 mg/l) were observed in khondalite and charnockite formations. A lower portion of the Godavari river basin, viz. East Godavari district was chosen for the study of the distribution of iron with special reference to the existing geological formations and the geomorphology of the area. The concentration of iron was observed to vary from below detection limit to 69 mg/l in the groundwater while it was less than 1 mg Fe/l in river and spring waters. The Fe of river water was reduced due to seawater mixing and the electrical conductivity (EC) was increased approximately to half of the seawater conductivity. Unlike the mixing of seawater at the surface, the same seawater mixing with groundwater yielded a water having similar order of EC with relatively high Fe. Fe was inversely related with nitrate in the groundwater. Fe was found to correlate considerably better with manganese in fluvial and coastal alluvium zones. The locations having higher Fe in delta are suspected to be related to palaeo channels. The association between Fe and Mn and their negative association with NO3 may be due to the possible autotrophic denitrification that might have taken place in the subsurface.

Frequency, Temperature and Salinity Variation of the Permittivity of Seawater

With the emergence of unmanned marine robots, underwater communication systems have received much attention in recent years. To successfully develop radio wave based communication solutions, it is essential to understand properties of electromagnetic wave transmission in seawater. These properties are determined by the frequency variation of the permittivity of seawater. Existing models for the permittivity of saline water are empirical ones that best fit experimental data. We propose a physically realistic model, similar to the one used in plasma physics, for the variation of the dielectric constant of water with varying frequencies and salinities. Our model is in excellent agreement with existing empirical fits for frequencies between 1 and 256 GHz. We use this model to study the propagation of electromagnetic waves in seawater. We explain that large propagation distances would be possible at MHz frequencies if the conductivity of seawater decreases at small field strengths due to the hydrogen bonding of water molecules. However, we were unable to experimentally verify any reduction in the conductivity of seawater