Thermodynamic Equation Of Seawater Research Articles

The salinity anomalies due to nutrients and inorganic carbon in the Bohai Sea

As a new seawater standard, the International Thermodynamic Equation of Seawater-2010 (TEOS-10) has made it possible to accurately calculate salinity changes caused by small changes in the relative proportions of inorganic dissolved constituents in the open ocean and thus to accurately calculate the thermodynamic properties of seawater. However, offshore and semi-enclosed seas are subject to the dual influence of geo-biochemical processes and terrestrial inputs, and the spatial and temporal variations in the relative composition of their seawater are more complex, resulting in very few studies of salinity change due to changes in the relative composition in these regions, and the applicability of the TEOS-10 in these seas needs to be further evaluated. The Bohai Sea is a typical semi-enclosed sea that has accumulated a large amount of physical oceanography and marine chemistry measurements, making it an ideal area to study the effects of changes in the relative composition of seawater on salinity. Based on repeated measurements of Section B in the Bohai Sea from 1985 to 2020, complemented by quasi-synchronous large-scale measurements of the Bohai Sea from 2006 to 2007, this study found that [HCO3−] and [Ca2+] ions anomalies dominate the relative composition anomalies of dissolved substances in this sea relative to the Standard Sea Water (SSW). These additional components could increase the absolute salinity SA by up to 0.1 g·kg-1 and the practical salinity SP by 0~0.04 according to the TEOS-10 algorithm and the mathematical model Pa08. Based on the specific environmental characteristics of the Bohai Sea, the sources, spatial and temporal variations, and influencing factors of the relative compositional anomalies are analyzed, and the empirical formulas of the absolute salinity anomaly δSA and practical salinity anomaly δSP for the Bohai Sea are further fitted, with the uncertainty of 0.007~0.021 g·kg-1 for δSA and 0.003~0.008 for δSP. The above results can not only improve the accuracy of the thermodynamic properties of the Bohai Seawater, but also provide the compatibility level of the long-term salinity changes in the Bohai Sea and its adjacent waters.

A thermodynamic potential of seawater in terms of Absolute Salinity, Conservative Temperature, and in situ pressure

Abstract. A thermodynamic potential is derived for seawater as a function of Conservative Temperature, Absolute Salinity and pressure. From this thermodynamic potential, all the equilibrium thermodynamic properties of seawater can be found, just as all these thermodynamic properties can be found from the TEOS-10 (the International Thermodynamic Equation of Seawater – 2010; IOC et al., 2010) Gibbs function (which is a function of in situ temperature, Absolute Salinity, and pressure). Present oceanographic practice in the Gibbs SeaWater Oceanographic Toolbox uses a polynomial expression for specific volume (and enthalpy) in terms of Conservative Temperature (as well as of Absolute Salinity and pressure), whereas the relationship between in situ temperature and Conservative Temperature is based on the Gibbs function. This mixed practice introduces (numerically small) inconsistencies and superfluous conversions between variables. The proposed thermodynamic potential of seawater, being expressed as an explicit function of Conservative Temperature, overcomes these small numerical inconsistencies, and in addition, the new approach allows for greater computational efficiency in the evaluation of sea surface temperature from Conservative Temperature. It is also shown that when using Conservative Temperature, the thermodynamic information in enthalpy is independent of that contained in entropy. This contrasts with the cases where either in situ temperature or potential temperature is used. In these cases, a single thermodynamic potential serves the important purpose of avoiding having to impose a separate consistency requirement between the functional forms of enthalpy and entropy.

Thermodynamics of Evaporation from the Ocean Surface

Adopted by the Intergovernmental Oceanographic Commission (IOC) of UNESCO in 2010 and the International Union of Geodesy and Geophysics (IUGG) in 2011, the Thermodynamic Equation of Seawater 2010 (TEOS-10) is the current geophysical standard for the thermodynamic properties of humid air, seawater and ice. TEOS-10 equations for evaporation and sublimation enthalpies are derived mathematically from the thermodynamic potential of a »sea air« model, denoting a multi-phase equilibrium composite of the geophysical aqueous mixtures. To estimating evaporation rates from the ocean, Dalton equations in various versions are implemented in numerical climate models. Some of those equations appear to be biased on climatic time scales if compared with proper thermodynamic driving forces. Such equations may lead to a spurious amplification of the hydrological cycle and an implied effect of cooling oceans. As an unbiased alternative, Dalton equations are proposed in terms of TEOS-10 relative fugacity (RF) or its conventional relative humidity (RH) approximations. With respect to RH uncertainties or trends, the substantial sensitivity of the evaporation flux may be estimated to be as much as 5 W m−2 per 1 %rh. Within a maximum error of only 0.04 %rh, sea-surface RF may be approximated in terms of dew-point or frost-point temperatures using a simple formula.

Review of Seawater Fiber Optic Salinity Sensors Based on the Refractive Index Detection Principle.

This paper presents a systematic review of the research available on salinity optic fiber sensors (OFSs) for seawater based on the refractive index (RI) measurement principle for the actual measurement demand of seawater salinity in marine environmental monitoring, the definition of seawater salinity and the correspondence between the seawater RI and salinity. To further investigate the progress of in situ measurements of absolute salinity by OFSs, the sensing mechanisms, research progress and measurement performance indices of various existing fiber optic salinity sensors are summarized. According to the Thermodynamic Equation of Seawater-2010 (TEOS-10), absolute salinity is recommended for sensor calibration and measurement. Comprehensive domestic and international research progress shows that fiber-optic RI sensors are ideal for real-time, in situ measurement of the absolute salinity of seawater and have excellent potential for application in long-term in situ measurements in the deep ocean. Finally, based on marine environmental monitoring applications, a development plan and the technical requirements of salinity OFSs are proposed to provide references for researchers engaged in related industries.

МЕТОД РАСЧЕТА СКОРОСТИ ЗВУКА В МОРСКОЙ ВОДЕ ДЛЯ ИЗМЕРЕНИЯ БЫСТРОМЕНЯЮЩИХСЯ ОКЕАНИЧЕСКИХ ПРОЦЕССОВ

The paper presents two compact polynomial equations expressing the dependence of the sound speed of sea water on the input parameters: in situ temperature, hydrostatic pressure and absolute salinity. The equations are obtained by approximating the standard International Thermodynamic Equation of Seawater-2010 (TEOS-10). The first equation is intended to be used for the technical purposes and reproduces the TEOS-10 data on the seawater sound speed over the wide range water environment parameters with a standard deviation of 0.987 cm/s. The second, more accurate equation is for the scientific use and reproduces the TEOS-10 data on the seawater sound speed over the oceanographic range water environment parameters with a standard deviation of 0.113 cm/s. The equations can be used to solve direct and inverse computational problems. In the direct computational problem, the sound speed value is calculated from the three input parameters measured values. In the inverse computational problem, the value of an unknown input parameter is determined from the measured values of the sound speed and two other input parameters. As a result of the experiments, the higher efficiency of the developed equations was confirmed in terms of their speed, saving energy and computer memory in comparison with the use of the International Equation TEOS-10. The developed equations, algorithms and programs for microcontrollers are convenient tools to equip various offshore platforms and especially fastmoving submersibles. The application of these equations makes it possible to obtain experimental data with high accuracy, to carry out measurements in real time in a rapidly changing aquatic environment, which can also be used to correct the movement of the submersibles.

Intercomparison of different state-of-the-art formulations of the mass density of humid air

The differences between one classical and three state-of-the-art formulations of the mass density of humid air were quantified. Here, we present both the calculi for direct determination of the humid-air mass density employing the virial form of the thermodynamic equation of state, and a sufficiently accurate look-up-table for the quick-look determination of the humid-air mass density, which is based on the advanced Thermodynamic Equation of Seawater 2010.

The interpretation of temperature and salinity variables in numerical ocean model output and the calculation of heat fluxes and heat content

Abstract. The international Thermodynamic Equation of Seawater 2010 (TEOS-10) defined the enthalpy and entropy of seawater, thus enabling the global ocean heat content to be calculated as the volume integral of the product of in situ density, ρ, and potential enthalpy, h0 (with reference sea pressure of 0 dbar). In terms of Conservative Temperature, Θ, ocean heat content is the volume integral of ρcp0Θ, where cp0 is a constant “isobaric heat capacity”. However, many ocean models in the Coupled Model Intercomparison Project Phase 6 (CMIP6) as well as all models that contributed to earlier phases, such as CMIP5, CMIP3, CMIP2, and CMIP1, used EOS-80 (Equation of State – 1980) rather than the updated TEOS-10, so the question arises of how the salinity and temperature variables in these models should be physically interpreted, with a particular focus on comparison to TEOS-10-compliant observations. In this article we address how heat content, surface heat fluxes, and the meridional heat transport are best calculated using output from these models and how these quantities should be compared with those calculated from corresponding observations. We conclude that even though a model uses the EOS-80, which expects potential temperature as its input temperature, the most appropriate interpretation of the model's temperature variable is actually Conservative Temperature. This perhaps unexpected interpretation is needed to ensure that the air–sea heat flux that leaves and arrives in atmosphere and sea ice models is the same as that which arrives in and leaves the ocean model. We also show that the salinity variable carried by present TEOS-10-based models is Preformed Salinity, while the salinity variable of EOS-80-based models is also proportional to Preformed Salinity. These interpretations of the salinity and temperature variables in ocean models are an update on the comprehensive Griffies et al. (2016) paper that discusses the interpretation of many aspects of coupled Earth system models.

Density and derived properties of standard seawater up to high pressure in stable and metastable states

In this work, a consolidated experimental apparatus for measuring the density of liquids, such as high pressure and metastable states, based on the isochoric method, was exploited to measure thermal properties of seawater. Density of standard seawater was measured in a wide range of temperature and pressure, specifically from (261.15 to 313.15) K and up to 110 MPa. All terms contributing to the uncertainty in determining the volume and the mass of the specimen were evaluated, obtaining a relative expanded uncertainty of seawater density around 0.03% (k=2). Experimental results were fitted by using a 8-parameters function of specific volume as a function of temperature and pressure. Using the obtained expression, density, isobaric thermal expansion, and isothermal compressibility of seawater were calculated from (263.15 to 313.15) K and for pressures between (1 and 105) MPa. A comparison with the predictions obtained by the Thermodynamic Equation of Seawater - 2010 (TEOS-10) shows a general good agreement that worsens when metastable states are considered.

Objective Analysis of SMOS and SMAP Sea Surface Salinity to Reduce Large-Scale and Time-Dependent Biases from Low to High Latitudes

AbstractTen years of L-band radiometric measurements have proven the capability of satellite sea surface salinity (SSS) to resolve large-scale-to-mesoscale SSS features in tropical to subtropical ocean. In mid-to-high latitudes, L-band measurements still suffer from large-scale and time-varying errors. Here, a simple method is proposed to mitigate the large-scale and time-varying errors. First, an optimal interpolation using a large correlation scale (~500 km) is used to map independently Soil Moisture Ocean Salinity (SMOS) and Soil Moisture Active Passive (SMAP) level-3 (L3) data. The mapping is compared with the equivalent mapping of in situ observations to estimate the large-scale and seasonal biases. A second mapping is performed on adjusted SSS at the scale of SMOS/SMAP spatial resolution (~45 km). This procedure merges both products and increases the signal-to-noise ratio of the absolute SSS estimates, reducing the root-mean-square difference of in situ satellite products by about 26%–32% from mid- to high latitudes, respectively, in comparison with the existing SMOS and SMAP L3 products. However, in the Arctic Ocean, some issues on satellite retrieved SSS related to, for example, radio frequency interferences, land–sea contamination, and ice–sea contamination remain challenging to reduce given the low sensitivity of L-band radiometric measurements to SSS in cold water. Using the International Thermodynamic Equation Of Seawater—2010 (TEOS-10), the resulting level-4 SSS satellite product is combined with satellite-microwave SST products to estimate sea surface density, spiciness, and haline contraction and thermal expansion coefficients. For the first time, we illustrate how useful these satellite-derived parameters are to fully characterize the surface ocean water masses at large mesoscale.

Effects of temperature and pressure on the threshold value of SBS LIDAR in seawater.

Effects of temperature and pressure on the threshold value of stimulated Brillouin scattering (SBS) in seawater were analyzed theoretically and experimentally. Theoretically, the change of threshold value of SBS versus the ocean depth was simulated based on the International Thermodynamic Equation of Seawater-2010 (TEOS-10) and the World Ocean Atlas 2013 (WOA13). Experimentally, an ocean temperature and pressure simulator (OTPS) was designed to measure the threshold value of SBS through simulating the changes of temperature and pressure of seawater in 0∼1000 meters. The theoretical and experimental results exhibit that the threshold value of SBS decreases with the increase of temperature at the same seawater pressure and increases with the increase of pressure at the same seawater temperature. The results imply that the SBS process is more likely to occur in upper seawater of lower-latitude areas. The theoretical and experimental results are helpful for remote sensing in ocean using the SBS LIDAR.

Anomalous salinity-density relations of seawater in the eastern central Atlantic

In the context of the recent oceanographic standard TEOS-10, the Thermodynamic Equation of Seawater – 2010, a new Reference-Composition Salinity Scale was introduced in 2008. For IAPSO Standard Seawater, values of this Reference Salinity are related to 1978 Practical Salinity by a definite factor, however, regional seawater samples may deviate from this equation. Over the past decade, various such salinity anomalies were investigated by direct density measurements and published in several studies. Typically, anomalies arise from non-dissociated solutes such as silicate which increase seawater density but not electrical conductivity. In contrast, negative density anomalies cannot be explained by added, electrically neutral salts, and their chemical or metrological origins remain elusive. In this paper, densities and Practical Salinities of seawater of the central eastern Atlantic Ocean in the region 18 °S to 33 °N, 22 °W to 12 °E are reported, measured between 2008 and 2013. Density anomalies in the range from 0 to –13 g m-3 were observed, consistent in magnitude with negative anomalies found by other authors elsewhere. No significant spatial or temporal trends of the anomalies could be observed.

Density of standard seawater by vibrating tube densimeter: Analysis of the method and results

Seawater density has a great importance in oceanography, since it drives the ocean currents that drift oxygen, heat, plankton and pollutants. If the density is measured with high accuracy, it can be also used for salinity determination. In this work, the density of standard seawater was measured at different absolute salinities from (10.044–38.178) g kg−1, in the temperature range of (278.15–313.15) K at atmospheric pressure. The measurements were carried out by means of a commercial vibrating tube densimeter, following the substitution method (alternating samples of seawater and water) and under conditions typical of the most oceanographic laboratories capabilities. Besides, an accurate analysis of the uncertainty of density was performed, obtaining a relative expanded uncertainty of 0.003% (k=2). Measurements were compared with the density values provided by the international reference equation of state: the Thermodynamic Equation of SeaWater-2010, TEOS-10.

Hydrography of the Central and Western Gulf of Mexico

AbstractThis study describes in detail the water masses of the Gulf of Mexico (GoM) west of 88°W based on their thermohaline properties and dissolved oxygen concentration. The existent historical information is complemented with new data from 14 cruises, Argo floats, and over one year of continuous glider monitoring. The results describe the general hydrography of the central and western GoM with focus on the difference between the water properties inside and outside Loop Current Eddies (LCEs). Caribbean Surface Water, Subtropical Underwater, and 18 °C Sargasso Sea Water (18SSW) are exclusive of the LCEs, and they are found along the LCEs preferred path between 23°N and 27°N. Outside the LCEs, the prominent characteristics of these water masses erode, and the Gulf Common Water is ubiquitous in the subsurface. It is shown that the water masses in the GoM need to be described in the frame of the dominant mesoscale features that take place there and that the dissolved oxygen is a key variable to identify some water masses of Caribbean origin as the Tropical Atlantic Central Water and the 18SSW. The previous potential temperature and salinity limits of the water masses within the GoM were revised and redefined in terms of absolute salinity and conservative temperature in the frame of the Thermodynamic Equation of Seawater, 2010 (TEOS‐10). While temperature values after conversion have little variation compared to the previous ones, the absolute salinity is in average 0.2 units greater than the former practical salinity.

Thermodynamic properties of seawater, ice and humid air: TEOS-10, before and beyond

Abstract. In the terrestrial climate system, water is a key player in the form of its different ambient phases of ice, liquid and vapour, admixed with sea salt in the ocean and with dry air in the atmosphere. For proper balances of climatic energy and entropy fluxes in models and observations, a highly accurate, consistent and comprehensive thermodynamic standard framework is requisite in geophysics and climate research. The new Thermodynamic Equation of Seawater – 2010 (TEOS-10) constitutes such a standard for properties of water in its various manifestations in the hydrological cycle. TEOS-10 was recommended internationally in 2009 by the Intergovernmental Oceanographic Commission (IOC) to replace the previous 1980 seawater standard, EOS-80, and in 2011 by the International Union of Geodesy and Geophysics (IUGG) as the official description for the properties of seawater, of ice and of humid air. This paper briefly reviews the development of TEOS-10, its novel axiomatic properties, the new oceanographic tools it offers and the important tasks that still await solutions by ongoing research. Among the latter are new definitions and measurement standards for seawater salinity and pH in order to establish their metrological traceability to the International System of Units (SI) for the first time after a century of widespread use. Of similar climatological relevance is the development and recommendation of a uniform standard definition of atmospheric relative humidity that is unambiguous and rigorously based on physical principles.The leading thermodynamic properties of a fluid are determined by the relations which exist between volume, pressure, temperature, energy, and entropy … But all the relations existing between these five quantities for any substance …may be deduced from the single relation existing for that substance between volume, energy, and entropy. Josiah Willard Gibbs, 1873b

Water Masses and Circulation in the Tropical Pacific off Central Mexico and Surrounding Areas

AbstractThe seasonal variations and the interactions of the water masses in the tropical Pacific off central Mexico (TPCM) and four surrounding areas were examined based on an extensive new hydrographic database. The regional water masses were redefined in terms of absolute salinity (SA) and conservative temperature (Θ) according to the Thermodynamic Equation of Seawater 2010 (TEOS-10). Hydrographic data and the evaporation minus (precipitation + runoff) balance were used to investigate the origin and seasonality of two salinity minima in the area. The shallow (50–100 m) salinity minimum originates with the California Current System and becomes saltier as it extends southeastward and mixes with tropical subsurface waters while the surface salinity minimum extends farther north in the TPCM in summer and fall because of the northward advection of tropical surface waters. The interactions between water masses allow a characterization of the seasonal pattern of circulation of the Mexican Coastal Current (MCC), the tropical branch of the California Current, and the flows through the entrance of the Gulf of California. The seasonality of the MCC inferred from the distribution of the water masses largely coincides with the geostrophic circulation forced by an annual Rossby wave.

Fine‐scale thermohaline ocean structure retrieved with 2‐D prestack full‐waveform inversion of multichannel seismic data: Application to the Gulf of Cadiz (SW Iberia)

AbstractThis work demonstrates the feasibility of 2‐D time‐domain, adjoint‐state acoustic full‐waveform inversion (FWI) to retrieve high‐resolution models of ocean physical parameters such as sound speed, temperature and salinity. The proposed method is first described and then applied to prestack multichannel seismic (MCS) data acquired in the Gulf of Cadiz (SW Iberia) in 2007 in the framework of the Geophysical Oceanography project. The inversion strategy flow includes specifically designed data preconditioning for acoustic noise reduction, followed by the inversion of sound speed in the shotgather domain. We show that the final sound speed model has a horizontal resolution of ∼ 70 m, which is two orders of magnitude better than that of the initial model constructed with coincident eXpendable Bathy Thermograph (XBT) data, and close to the theoretical resolution of O(λ). Temperature (T) and salinity (S) are retrieved with the same lateral resolution as sound speed by combining the inverted sound speed model with the thermodynamic equation of seawater and a local, depth‐dependent T‐S relation derived from regional conductivity‐temperature‐depth (CTD) measurements of the National Oceanic and Atmospheric Administration (NOAA) database. The comparison of the inverted T and S models with XBT and CTD casts deployed simultaneously to the MCS acquisition shows that the thermohaline contrasts are resolved with an accuracy of 0.18oC for temperature and 0.08 PSU for salinity. The combination of oceanographic and MCS data into a common, pseudo‐automatic inversion scheme allows to quantitatively resolve submeso‐scale features that ought to be incorporated into larger‐scale ocean models of oceans structure and circulation.

Melting of Ice and Sea Ice into Seawater and Frazil Ice Formation

Abstract The thermodynamic consequences of the melting of ice and sea ice into seawater are considered. The International Thermodynamic Equation Of Seawater—2010 (TEOS-10) is used to derive the changes in the Conservative Temperature and Absolute Salinity of seawater that occurs as a consequence of the melting of ice and sea ice into seawater. Also, a study of the thermodynamic relationships involved in the formation of frazil ice enables the calculation of the magnitudes of the Conservative Temperature and Absolute Salinity changes with pressure when frazil ice is present in a seawater parcel, assuming that the frazil ice crystals are sufficiently small that their relative vertical velocity can be ignored. The main results of this paper are the equations that describe the changes to these quantities when ice and seawater interact, and these equations can be evaluated using computer software that the authors have developed and is publicly available in the Gibbs SeaWater (GSW) Oceanographic Toolbox of TEOS-10.

Limnological applications of the Thermodynamic Equation of Seawater 2010 (TEOS‐10)

The new Thermodynamic Equation of Seawater 2010 (TEOS‐10) provides a highly accurate, thermodynamically consistent, and complete representation of all thermodynamic properties of seawater over a wide range in temperature and salinity. These properties include density, sound speed, heat capacity, enthalpy, chemical potential, and many others. Here we provide simple procedures by which limnological studies can take advantage of TEOS‐10. These require replacing the TEOS‐10 salinity argument, seawater Absolute Salinity SA, with a limnological salinity Sa. In typical natural waters where anion concentrations are dominated by HCO3− or Cl−, Sa can be approximated by the solution salinity Sasoln, obtained by summing the concentrations of different dissolved constituents in a complete chemical analysis after multiplying by their molar masses. Slightly better results can be obtained, especially at very low salinities where silicic acid Si(OH)4 is an important constituent, by using a density salinity Sadens carefully defined by dividing the solution salinity into an ionic and a nonionic part and changing the weighting factors for each in the summation. In cases where the dominant anion is HCO3−, which covers the majority of inland waters, measurements of electrical conductivity can be used to estimate the ionic salinity, which will be ≈60% greater than the Absolute Salinity of seawater of the same conductivity. The resulting estimates of that part of density in excess of pure water density at the same temperature will be accurate within ± 10%.

Replacement of EOS‐80 with the International Thermodynamic Equation of Seawater – 2010 (TEOS‐10)

Replacement of EOS‐80 with the International Thermodynamic Equation of Seawater – 2010 (TEOS‐10)

Announcement - Replacement of EOS-80 with the International Thermodynamic Equation of Seawater - 2010 (TEOS-10)

Announcement - Replacement of EOS-80 with the International Thermodynamic Equation of Seawater - 2010 (TEOS-10)