物理海洋学名词-S 372

Glossary of Physical Oceanography and Related Disciplines

Steven K. Baum Department of Oceanography Texas A&M University

May 26, 2004

 

SAHFOS Abbreviation for Sir Alister Hardy Foundation for Ocean Science, whose mission is to further the understanding of marine pelagic ecosystem processes through:
• the maintenance and expansion of the Continuous Plankton Recorder (CPR) survey;
• cooperation in the establishment of global long–term oceanic plankton monitoring programs;
• the development of new sampling and sensor systems; and
• the dissemination of the results of original research.
It was originally established in 1990 to operate the CPR survey, a program started in 1931 by Alister Hardy.
[http://www.npm.ac.uk/sahfos/sahfos.html]


saline contraction coefficient A quantity arising from taking derivatives of the density in the (p,θ,S) representation of the equation of state. This is defined in seawater as:
β =1/ρ*∂ρ/∂S|_(θ,ρ)=1/ρ*∂ρ/∂S|_(T,ρ)+α*∂θ/∂S|_(T,ρ)
where ρ is the in situ density, θ is the potential temperature, S is the salinity, and T is the temperature. In practice, ∂ρ/∂S can be obtained from the International Equation of State of seawater, and ∂θ/∂S from Bryden [1973].
McDougall [1987b] gives a polynomial expression for β:
β=0.785567×10^(−3)−0.301985×10^(−5)*θ+0.555579×10^(−7)*θ^2−0.415613×10^(−9)*θ^3+(S−35.0)*[−0.356603×10^(−6)+0.788212×10^(−8)*θ+0.408195×10^(−10)*p−0.602281×10^(−15)*p^2]+(S−35.0)^2*[+0.515032×10^−8]+p*[−0.121555×10^(−7)+0.192867×10^(−9)*θ−0.213127×10^(−11)*θ^2]+p^2*[+0.176621×10^(−12)−0.175379×10^(−14)*θ]+p^3[+0.121551×10^(−17)]
The units of β are psu^(−1) and the rms error of this fit is 0.163×10^(−6) psu^(−1). A test value is 0.72088×10^−3 psu^−1 at S = 40 psu, θ = 10.0◦C and p = 4000.0 db. See McDougall et al. [1987] and the related thermal expansion coefficient and adiabatic compressibility.


salinity An oceanographic concept conceived to provide a measure of the mass of salt per unit mass of seawater. The first systematic attempt to define this was made by a commission appointed by the International Council for the Exploration of the Sea in 1899 and chaired by Knudsen. Attempts to measure salt content by drying samples were accompanied by losses of volatile compounds along with the water, and the hygroscopic nature of the residue also served to complicate matters. A dry residue method where the sample was evaporated and dried to a stable weight at 480◦C after processing with hydrochloric acid was offered as an alternative method. This led to the definition of the salinity as “the total amount of solid material in grams contained in one kilogram of seawater when all the carbonate has been converted to oxide, all the bromine and iodine replaced by chlorine, and all the organic material oxidized.”

When this dry residue method also provided practical difficulties aboard ship the commission defined a chlorinity that could be determined via a volumetric titration using silver nitrate. This measurement could be combined with the assumption of constant ionic ratios in seawater to obtain a measure of the salinity, with the relationship between the two quantities being defined as
S(◦/◦◦) = 0.03 + 1.805 Cl(◦/◦◦).
A small adjustment was made in the definition of chlorinity in the late 1920s, but it remained basically the same until the development of reliable and precise electronic instrumentation in the 1950s led to a qualitative redefinition of the chlorinity, and therefore the salinity, in terms of measurements of the electrical conductivity of a water sample. This led to the creation and publication of the the International Oceanographic Tables giving salinity as a function of conductivity ratio above 10◦. These tables were adequate for the laboratory determination of salinity, but could not be used with in-situ salinometers since most such measurements were made at temperatures below 10◦C. A separate set of tables were developed in the mid-1960s that covered the range 0-30◦C, although this led to discrepancies between in-situ and bench measurements of salinities and many separate attempts to patch together the two data sets. This in turn led to confusion in the comparison of salinity data amongst the major oceanographic institutes.
A solution was found in 1978 in the form of a new definition called the Practical Salinity Scale (PSS–78) where the practical salinity is defined in terms of the ratio of the electrical conductivity of a seawater sample at atmospheric pressure at 15◦C to that of KCl solution containing 32.4356 g of KCl in a mass of 1 kg of solution at the same pressure and temperature. See Lewis [1980] and Lewis and Perkin [1978].

 

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