Ocean Science www.ocean-sci.net 1812-0784 1812-0792 6 1 2010 10.5194/os-6-361-2010 http://www.ocean-sci.net/6/361/2010/ http://www.ocean-sci.net/6/361/2010/os-6-361-2010.html http://www.ocean-sci.net/6/361/2010/os-6-361-2010.pdf 361 378 2010-03-18 A model for predicting changes in the electrical conductivity, practical salinity, and absolute salinity of seawater due to variations in relative chemical composition R. Pawlowicz rich@eos.ubc.ca Dept. of Earth and Ocean Sciences, University of British Columbia, Canada 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. Bacon, S., Culkin, F., Higgs, N., and Ridout, P.: IAPSO Standard Seawater: Definition of the Uncertainty in the Calibration Procedures and Stability of Recent Batches, J. Atmos. Ocean. Tech., 24, 1785–1799, 2007. Brewer, P G. and Bradshaw, A.: The effect of the non-ideal composition of seawater on salinity and density, J. Mar. Res., 33, 157–175, 1975. Chen, C.-T A.: Shelf-vs. dissolution-generated alkalinity above the chemical lysocline, Deep-Sea Res. Pt. II, 49, 5365–5375, 2002. Conners, D N. and Kester, D R.: Effect of the major ion variations in the marine environment on the specific gravity-conductivity-chlorinity-salinity relationship, Mar. Chem., 2, 301–314, 1974. Conners, D N. and Park, K.: The partial equivalent conductances of electrolytes in seawater: a revision, Deep-Sea Res., 14, 481–484, 1967. Conners, D N. and Weyl, P K.: The partial equivalent conductances of salts in seawater and the density/conductance relationship, Limnol. Oceanogr., 13, 39–50, 1968. Corti, H., Crovetto, R., and Fernández-Prini, R.: Mobilities and Ion-Pairing in LiB(OH)4 and NaB(OH)4 Aqueous Solutions. A Conductivity Study, J. Solution Chem., 9, 617–625, 1980. de Villiers, S.: Excess dissolved Ca in the deep ocean: a hydrothermal hypothesis, Earth Planet. Sc. Lett., 164, 627–641, 1998. de Villiers, S. and Nelson, B K.: Detection of Low-Temperature Hydrothermal Fluxes by Seawater Mg and Ca Anomalies, Science, 285, 721–723, 1999. Dickson, A G., Sabine, C L., and Christian, J R. (Eds.): Guide to best practices for ocean CO2 measurements, PICES Special Publication 3, 2007. Feistel, R.: A Gibbs function for seawater thermodynamics for −6 to 80 °C and salinity up to 120 g kg−1, Deep-Sea Res. Pt. I, 55, 1639–1671, 2008. Goyet, C., Poisson, A., Brunet, C., and Culkin, F.: IAPSO Standard Seawater as a reference standard for alkalinity determinations, Deep-Sea Res., 32, 1437–1443, 1985. Hall, K J. and Northcote, T G.: Conductivity-Temperature standardization and dissolved solids estimation in a meromictic saline lake, Can. J. Fish. Aquat. Sci., 43, 2450–2454, 1986. Hill, K D., Dauphinee, T M., and Woods, D J.: The Extension of the Practical Salinity Scale 1978 to Low Salinities, IEEE J. Oceanic Eng., OE-11, 109–112, 1986a. Hill, K D., Dauphinee, T M., and Woods, D J.: A comparison of the Temperature Coefficients of Electrical Conductivity of Atlantic and Pacific Seawaters, IEEE J. Oceanic Eng., OE-11, 485–486, 1986b. Jellison, R., Macintyre, S., and Millero, F J.: Density and conductivity properties of Na-CO3-Cl-SO4 brine from Mono Lake, California, USA, Int. J. Salt Lake Res., 8, 41–53, 1999. Kawano, T., Aoyama, M., Joyce, T., Uchida, H., Takatsuki, Y., and Fukasawa, M.: The Latest batch-to-batch Difference Table of Standard Seawater and Its Application to the WOCE Onetime Sections, J. Oceanogr., 62, 777–792, 2006. Lewis, E L. and Perkin, R G.: Salinity: Its definition and Calculation, J. Geophys. Res., 83, 466–478, 1978. McDougall, T. J., Jackett, D. R., and Millero, F. J.: An algorithm for estimating Absolute Salinity in the global ocean, Ocean Sci. Discuss., 6, 215–242, 2009. Millero, F J.: The Physical Chemistry of Estuaries, in: Marine Chemistry in the Coastal Environment, edited by: Church, T M., American Chemical Society, 25–55, 1975. Millero, F J.: The conductivity-density-salinity-chlorinity relationships for estuarine waters, Limnol. Oceanogr., 29, 1317–1321, 1984. Millero, F J.: Thermodynamics of the carbon dioxide system in the oceans, Geochim. Cosmochim. Ac., 59, 661–677, 1995. Millero, F J.: Effect of changes in the composition of seawater on the density-salinity relationship, Deep-Sea Res. Pt. I, 47, 1583–1590, 2000. Millero, F J. and Poisson, A.: International one-atmosphere equation of state for seawater, Deep-Sea Res., 28A, 625–629, 1981. Millero, F J., Lawson, D., and Gonzalez, A.: The Density of Artificial River and Estuarine Waters, J. Geophys. Res., 81, 1177–1179, 1976. Millero, F J., Zhang, J. Z., Lee, K., and Campbell, D M.: Titration alkalinity of seawater, Mar. Chem., 44, 153–165, 1993. Millero, F J., Feistel, R., Wright, D G., and McDougall, T J.: The composition of Standard Seawater and the definition of the Reference-Composition Salinity Scale, Deep-Sea Res. Pt. I, 55, 50–72, 2008. Nozaki, Y.: A fresh look at element distribution in the North Pacific Ocean, EOS, Transactions American Geophysical Union, 78, 221–221, doi:10.1029/97EO00148, 1997. Park, K.: Partial equivalent conductance of electrolytes in seawater, Deep-Sea Res., 11, 729–736, 1964. Pawlowicz, R.: Calculating the conductivity of natural waters, Limnol. Oceanogr.-Meth., 6, 489–501, 2008. Perkin, R G. and Lewis, E L.: The Practical Salinity Scale 1978: Fitting the Data, IEEE J. Oceanic Eng., OE-5, 9–16, 1980. Poisson, A., Périé, M., Périé, J., and Chemla, M.: Individual equivalent conductances of the major ions in seawater, J. Solution Chem., 8, 377–394, 1979. Sarmiento, J L. and Gruber, N.: Ocean Biogeochemical Dynamics, Princeton University Press, Princeton, 2006. Soffyn-Egli, P. and Mackenzie, F T.: Mass balance of dissolved lithium in the oceans, Geochim. Cosmochim. Ac., 48, 859–872, 1984. Unesco/ICES/SCOR/IAPSO joint panel on oceanographic tables and standards: Background papers and supporting data on the Practical Salinity Scale 1978, Unesco technical papers in marine science 37, 1981. Vollmer, M K., Weiss, R F., Williams, R T., Falkner, K K., Qiu, X., Ralph, E A., and Romanovsky, V V.: Physical and chemical properties of the waters of saline lakes and their importance for deep-water renewal: Lake Issyk-Kul, Kyrgyzstan, Geochim. Cosmochim. Ac., 66, 4235–4246, 2002. Watanabe, H. and Iizuka, K.: The influence of dissolved gases on the density of water, Metrologia, 21, 19–26, 1985. Wüest, A., Piepke, G., and Halfman, J D.: Combined effects of dissolved solids and temperature on the density stratification of Lake Malawi, in: The Limnology, Climatology, and Paleoclimatology of the East African Lakes, edited by: Johnson, T C. and Odada, E O., Gordon and Breach, Australia, 183–204, 1996.