Density of Standard Seawater from 298.15 K Down to the Supercooled Liquid Region and up to 110 MPa

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

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.

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%.

Speed of sound measurements in North Atlantic Seawater and IAPSO Standard Seawater up to 70 MPa

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

We expanded the batch-to-batch offsets of The International Association for the Physical Sciences of the Oceans (IAPSO) Standard Seawater (SSW) batches P145–P163 by intercomparison measurements using salinometers. On the basis of our results, we recommend using the correction factors instead of the offsets to correct the batch-to-batch differences, especially for salinity data outside the range of 30–40 g kg−1. We evaluated the expanded batch-to-batch correction factors by applying them to time series salinity data collected in the northwestern North Pacific Ocean and found that they are effective for detecting recent freshening (−0.6 ± 0.1 × 10−3 g kg−1 decade−1) in the deep North Pacific, which might be related to a reduction of the formation rate of Antarctic Bottom Water. We also evaluated the SSW linearity pack by applying the batch-to-batch correction factors. Linearity errors of the salinometers estimated from decade resistance substituters were consistent with the results of the linearity pack measurements. To correct the linearity errors of a salinometer, it might be suitable to use the more detailed distribution of those estimated from the decade resistance substituter than the linearity pack measurements. Since the cause of large batch-to-batch differences is still unclear, a reference seawater that is more robust and stable than SSW might be necessary to establish a high-level of international comparability of salinity measurements; the Multiparametric Standard Seawater (MSSW) currently under development might be a candidate for such reference seawater, because MSSW is expected to be more stable than SSW not only in practical salinity but also in absolute salinity.

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

Seawater density has a great importance in the oceanographic science, since it can be used for salinity determination, if density is known with the necessary accuracy. For that reason, a review of the methods for density measurements suitable for seawater measurements is presented. Furthermore, in this work standard seawater density is measured at different practical salinities (from 9.997 to 37.999) in the temperature range between (278.15 to 308.15) K at ambient pressure. Measurements are carried out by means of a vibrating tube densimeter and following the substitution method (alternating samples of seawater and ordinary water). Besides, an accurate analysis of the density uncertainty has been performed, obtaining an expanded uncertainty of 0.004%. Measurements are carried out and compared with density results given in the literature, performed with the same technique.

Abstract. The brackish water of the Baltic Sea is a mixture of ocean water from the Atlantic/North Sea with fresh water from various rivers draining a large area of lowlands and mountain ranges. The evaporation-precipitation balance results in an additional but minor excess of fresh water. The rivers carry different loads of salts washed out of the ground, in particular calcium carbonate, which cause a composition anomaly of the salt dissolved in the Baltic Sea in comparison to Standard Seawater. Directly measured seawater density shows a related anomaly when compared to the density computed from the equation of state as a function of Practical Salinity, temperature and pressure. Samples collected from different regions of the Baltic Sea during 2006–2009 were analysed for their density anomaly. The results obtained for the river load deviate significantly from similar measurements carried out forty years ago; the reasons for this decadal variability are not yet fully understood. An empirical formula is derived which estimates Absolute from Practical Salinity of Baltic Sea water, to be used in conjunction with the new Thermodynamic Equation of Seawater 2010 (TEOS-10), endorsed by IOC/UNESCO in June 2009 as the substitute for the 1980 International Equation of State, EOS-80. Our routine measurements of the samples were accompanied by studies of additional selected properties which are reported here: conductivity, density, chloride, bromide and sulphate content, total CO2 and alkalinity.

Ten 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.

Physico-chemical study of Dead Sea waters: II. Density measurements and equation of state of Dead Sea waters at 1 atm

Abstract. The determination of salinity by means of electrical conductivity relies on stable salt proportions in the North Atlantic Ocean, because standard seawater, which is required for salinometer calibration, is produced from water of the North Atlantic. To verify the long-term stability of the standard seawater composition, it was proposed to perform measurements of the standard seawater density. Since the density is sensitive to all salt components, a density measurement can detect any change in the composition. A conversion of the density values to salinity can be performed by means of a density–salinity relation. To use such a relation with a target uncertainty in salinity comparable to that in salinity obtained from conductivity measurements, a density measurement with an uncertainty of 2 g m−3 is mandatory. We present a new density–salinity relation based on such accurate density measurements. The substitution measurement method used is described and density corrections for uniform isotopic and chemical compositions are reported. The comparison of densities calculated using the new relation with those calculated using the present reference equations of state TEOS-10 suggests that the density accuracy of TEOS-10 (as well as that of EOS-80) has been overestimated, as the accuracy of some of its underlying density measurements had been overestimated. The new density–salinity relation may be used to verify the stable composition of standard seawater by means of routine density measurements.

Density of standard seawater solutions at atmospheric pressure

The speed of sound in 2-methyl-2,4-pentanediol has been measured in the temperature range from (293.15 to 318.15) K at pressures up to 101 MPa by the pulse-overlap method. The speed of sound at atmospheric pressure has been measured in the temperature range from (283.15 to 323.15) K by means of the same method. The density has been measured in the temperature range from (278.15 to 358.15) K under atmospheric pressure with a vibrating tube densimeter. The isobaric heat capacity has been measured in the temperature range from (284 to 358) K under atmospheric pressure with a differential scanning calorimeter. The experimental results have been used to calculate densities, isobaric heat capacities, the isobaric coefficient of thermal expansion, and isentropic and isothermal compressibilities in function of temperature and pressure; the effects of pressure and temperature have been discussed.

Deep-Sea Research, 1966, Vol. 13, pp. 975 to 976. Pergamon Press Ltd. Printed in Great Britain. Some implications of the 1940 redefinition of chlorinity* W. S. REESURGH (Received 13 January 1966) EFFORTS to refine the relationships of sea water density, electrical conductivity, and refractive index as functions of chlorinity and temperature have led to plans for the redetermination of these properties on a large number of well-distributed sea water samples. The new values will doubtless be compared with those from earlier studies. A precaution that must be taken to obtain a reliable comparison deals with differences in the meaning of chlorinity during the 1930's and implications of these differences on interpretation of properties measured as a function of chlorinity. These differences and their implications have not been specifically mentioned in recent reviews (Cox, 1963, 1965; JOHNSTON, 1964; PARK and BuRr, 1965) and appear to have been overlooked by a number of workers. The word chlorinity was defined by FORCH, KNLrOSEr~ and SORENSON (1902) as the total weight of halides, calculated as chlorine, in a kilogram of sea water. This stated definition was dependent on the choice of atomic weight values. Standard Sea Water provided a convenient working standard. This working standard was independent of changes in atomic weight values since all batches of Standard Sea Water were compared directly or indirectly with a primary standard sea water whose chlorinity was determined according to the stated definition using KCI (1900 atomic weight values) as the standard. By 1940, changes in atomic weight values led to a difference between the stated definition and the working standard of about 0-05 % (0'009~oo). To avoid this difficulty, JACOBSEN and KNtrOSEN (1940) redefined chlorinity as : The number giving the chlorinity in grams per kilogram of sea water sample is identical with the mass in grams of ' a t o m i c weight silver' just necessary to precipitate the halogens in 0'3285233 kilogram of sea water sample. Chlorinity is, according to this definition, independent of changes in atomic weight values and numerically identical to the chlorinity defined by FORCH, KNUDSEN and SORENSON in 1902. Standard Sea Water provides a working standard as before. During the 1930's, comprehensive investigations of the chlorinity and temperature dependence of the electrical conductivity and refractive index of sea water were performed by Dr. Thomas G. Thompson and his co-workers at the University of Washington, Seattle. The values obtained during these investigations have since seen wide use. In their work on electrical conductivity (THOMAS et al., 1934) and refractive index (UTrERBACK et aL, 1934), identical sea water samples were studied. Care- fully purified NaCI (1932 atomic weight values) was used as the standard in their Volhard chlorinity titrations. Standard Sea Water was not mentioned. It should be made clear that their reported chlorinities actually were chlorinities in 1934, but following the redefinition of chlorinity by JACOBSEN and KNtrDSEN (1940), they have become measurements of chlorine-equivalent. These chlorine- equivalent measurements have been widely interpreted as chlorinities, resulting in a number of erroneous tables and interpolation formulae. Since the pertinent atomic weight values were not changed between 1932 and 1940, the ratio of chlorine-equivalent to chlorinity reported by LYMAN and FLEMING (1940) may be used to convert these reliable measurements of chlorine-equivalent to chlorinity. In comparing recent and future work to that of THOMAS et al. (1934) and UTrERaACK et aL (1934), their reported c h l o r i n i t i e s should be divided by 1-00045 to obtain true chlorinities. *Contribution No. 84 of Chesapeake Bay Institute and the Department of Oceanography, The Johns Hopkins University. This study was supported by the Office of Naval Research, under Contract N o n r 4010(11), N R 083-016.