## Contents

## USAGE:

sigma4 = gsw_sigma4(SA,CT)

## DESCRIPTION:

Calculates potential density anomaly with reference pressure of 4000
dbar, this being this particular potential density minus 1000 kg/m^3.
This function has inputs of Absolute Salinity and Conservative
Temperature. This function uses the computationally-efficient
75-term expression for specific volume in terms of SA, CT
and p (Roquet et al., 2015).

Note that the 75-term equation has been fitted in a restricted range of
parameter space, and is most accurate inside the "oceanographic funnel"
described in McDougall et al. (2003). The GSW library function
"gsw_infunnel(SA,CT,p)" is avaialble to be used if one wants to test if
some of one's data lies outside this "funnel".

## INPUT:

SA = Absolute Salinity [ g/kg ]
CT = Conservative Temperature [ deg C ]

SA & CT need to have the same dimensions.

## OUTPUT:

sigma4 = potential density anomaly with [ kg/m^3 ]
respect to a reference pressure of 4000 dbar,
that is, this potential density - 1000 kg/m^3.

## EXAMPLE:

SA = [34.7118; 34.8915; 35.0256; 34.8472; 34.7366; 34.7324;]
CT = [28.8099; 28.4392; 22.7862; 10.2262; 6.8272; 4.3236;]

sigma4 = gsw_sigma4(SA,CT)

sigma4 =

37.900374609834898
38.166979617032439
40.280876075282549
43.896091033421953
44.631677245327637
45.171817312020039

## AUTHOR:

Trevor McDougall & Paul Barker [ help@teos-10.org ]

## VERSION NUMBER:

3.05 (16th February, 2015)

## REFERENCES:

IOC, SCOR and IAPSO, 2010: The international thermodynamic equation of
seawater - 2010: Calculation and use of thermodynamic properties.
Intergovernmental Oceanographic Commission, Manuals and Guides No. 56,
UNESCO (English), 196 pp. Available from the TEOS-10 web site.
See Eqn. (A.30.1) of this TEOS-10 Manual.

McDougall, T.J., D.R. Jackett, D.G. Wright and R. Feistel, 2003:
Accurate and computationally efficient algorithms for potential
temperature and density of seawater. J. Atmosph. Ocean. Tech., 20,
pp. 730-741.

Roquet, F., G. Madec, T.J. McDougall, P.M. Barker, 2015: Accurate
polynomial expressions for the density and specifc volume of seawater
using the TEOS-10 standard. Ocean Modelling.

The software is available from http://www.TEOS-10.org