Compute $$\sigma_\theta$$, the potential density of seawater (minus 1000 kg/m$$^3$$), referenced to surface pressure.

swSigma0(
salinity,
temperature = NULL,
pressure = NULL,
longitude = NULL,
latitude = NULL,
eos = getOption("oceEOS", default = "gsw")
)

## Arguments

salinity either practical salinity (in which case temperature and pressure must be provided) or an oce object, in which case salinity, temperature (in the ITS-90 scale; see next item), etc. are inferred from the object. in-situ temperature ($$^\circ$$C), defined on the ITS-90 scale. This scale is used by GSW-style calculation (as requested by setting eos="gsw"), and is the value contained within ctd objects (and probably most other objects created with data acquired in the past decade or two). Since the UNESCO-style calculation is based on IPTS-68, the temperature is converted within the present function, using T68fromT90(). pressure (dbar) longitude of observation (only used if eos="gsw"; see ‘Details’). latitude of observation (only used if eos="gsw"; see ‘Details’). equation of state, either "unesco" (references 1 and 2) or "gsw" (references 3 and 4).

## Value

Potential density anomaly (kg/m$$^3$$).

## Details

Definition: $$\sigma_0=\sigma_\theta=\rho(S,\theta(S,t,p),0$$

• 1000 kg/m$$^3$$.

## References

See citations provided in the swRho() documentation.