The effects of biogeochemical processes on oceanic conductivity/salinity/ density relationships and the characterization of real seawater

Abstract. As seawater circulates through the global ocean, its relative composition undergoes small variations. This results in changes to the conductivity/salinity/density relationship, which is currently well-defined only for Standard Seawater obtained from a particular area in the North Atlantic. These changes are investigated here by analysis of laboratory experiments in which salts are added to seawater, by analysis of oceanic observations of density and composition anomalies, and by mathematical investigation using a model relating composition, conductivity, and density of arbitrary seawaters. Mathematical analysis shows that understanding and describing the effect of changes in relative composition on operational estimates of salinity using the Practical Salinity Scale 1978 and on density using an equation of state for Standard Seawater require the use of a number of different salinity variables and a family of haline contraction coefficients. These salinity variables include an absolute Salinity SAsoln, a density salinity SAdens, the reference salinity SR, and an added-mass salinity SAadd. In addition, a new salinity variable S∗ is defined, which represents the preformed salinity of a Standard Seawater component of real seawater to which biogeochemical processes add material. In spite of this complexity, observed correlations between different ocean biogeochemical processes allow the creation of simple formulas that can be used to convert between the different salinity and density measures, allowing for the operational reduction of routine oceanographic observations.

[1]  F. Millero,et al.  The density of North Pacific Ocean waters , 1978 .

[2]  Fen Huang,et al.  The density of seawater as a function of salinity (5 to 70 g kg 1 ) and temperature (273.15 to 363.15 K) , 2009 .

[3]  F. Millero,et al.  THE PARTIAL MOLAL VOLUMES OF ELECTROLYTES IN 0.725 M SODIUM CHLORIDE SOLUTIONS AT 25°C , 1977 .

[4]  F. Millero,et al.  The Apparent Molal Volume and Compressibility of Seawater Fit to the Pitzer Equations , 2000 .

[5]  F. Millero,et al.  The effect of pressure on the ionization of water at various temperatures from molal-volume data1 , 1972 .

[6]  F. Millero.  The physical chemistry of natural waters , 1985 .

[7]  J. F. Waters,et al.  The effect of composition on the density of South Pacific Ocean waters , 2009 .

[8]  Rich Pawlowicz,et al.  A model for predicting changes in the electrical conductivity, practical salinity, and absolute salinity of seawater due to variations in relative chemical composition , 2010 .

[9]  Andrew G. Dickson,et al.  Guide to best practices for ocean CO2 measurements , 2007 .

[10]  R. Feistel.  Extended equation of state for seawater at elevated temperature and salinity , 2010 .

[11]  J. Willey,et al.  The partial molal volume of silicic acid in 0.725 m NaCl , 1976 .

[12]  F. Millero.  Effect of changes in the composition of seawater on the density–salinity relationship , 2000 .

[13]  S. Seitz,et al.  CCQM-P111 study on traceable determination of practical salinity and mass fraction of major seawater components , 2010 .

[14]  Frank J. Millero,et al.  An algorithm for estimating Absolute Salinity in the global ocean , 2009 .

[15]  F. Millero.  Thermodynamics of the carbon dioxide system in the oceans , 1995 .

[16]  G. Pavlova,et al.  Distribution of alkalinity and dissolved calcium in the Sea of Okhotsk , 2008 .

[17]  F. Millero.  The Physical Chemistry of Estuaries , 1975 .

[18]  P. Brewer,et al.  The density of North Atlantic and North Pacific deep waters , 1976 .

[19]  Nicholas R. Bates,et al.  The Arctic Ocean marine carbon cycle: evaluation of air-sea CO 2 exchanges, ocean acidification impacts and potential feedbacks , 2009 .

[20]  Rich Pawlowicz,et al.  Calculating the conductivity of natural waters , 2008 .

[21]  C. Chen.  Shelf-vs. dissolution-generated alkalinity above the chemical lysocline , 2002 .

[22]  F. Millero,et al.  Densities and compressibilities of aqueous sodium carbonate and bicarbonate from 0 to 45°C , 1983 .

[23]  R. Feely,et al.  The universal ratio of boron to chlorinity for the North Pacific and North Atlantic oceans , 2010 .

[24]  C. Monnin,et al.  Density calculation and concentration scale conversions for natural waters , 1994 .

[25]  F. Millero,et al.  The (p, V, T) properties of concentrated aqueous electrolytes I. Densities and apparent molar volumes of NaCl, Na2SO4, MgCl2, and MgSO4 solutions from 0.1 mol·kg−1 to saturation and from 273.15 to 323.15 K , 1982 .

[26]  F. Millero,et al.  The density and expansibility of artificial seawater solutions from 0 to 40°C and 0 to 21‰ chlorinity , 1973 .

[27]  Zhenhao Duan,et al.  The P,V,T,x properties of binary aqueous chloride solutions up to T=573 K and 100 MPa , 2008 .

[28]  J. F. Waters,et al.  The effect of composition on the density of Indian Ocean waters , 2008 .

[29]  R. G. Perkin,et al.  Salinity: Its definition and calculation , 1978 .

[30]  S. Villiers.  Excess dissolved Ca in the deep ocean: a hydrothermal hypothesis , 1998 .

[31]  T. McDougall,et al.  Absolute Salinity, ''Density Salinity'' and the Reference-Composition Salinity Scale: present and future use in the seawater standard TEOS-10 , 2010 .

[32]  F. Millero.  Molal volumes of electrolytes , 1971 .

[33]  Rainer Feistel,et al.  A Gibbs function for seawater thermodynamics for -6 to 80 °C and salinity up to 120gkg-1 , 2008 .

[34]  T. McDougall,et al.  The composition of Standard Seawater and the definition of the Reference-Composition Salinity Scale , 2008 .

[35]  Hideo Watanabe,et al.  ERRATUM: The Influence of Dissolved Gases on the Density of Water , 1985 .

[36]  F. Millero,et al.  The effect of pressure on the ionization of boric acid in aqueous solutions from molal-volume data , 1974 .

[37]  R. Feistel,et al.  A Gibbs–Pitzer function for high-salinity seawater thermodynamics , 2007 .

[38]  F. Millero,et al.  thermodynamic properties for natural waters covering only the limnological range1 , 1986 .