either salinity [PSU] (in which case
temperature and pressure must be provided) or
a ctd object (in which case salinity,
temperature and pressure ar
temperature
in-situ temperature [$^\circ$C]
pressure
pressure [dbar]
longitude
longitude of observation (only used if eos="gsw"; see
Details).
latitude
latitude of observation (only used if eos="gsw"; see
Details).
eos
equation of state, either "unesco" [1,2] or "gsw"
[3,4].
Value
Lapse rate [$deg$C/m].
Details
If the first argument is a ctd object, then salinity, etc. are
extracted from it, and used for the calculation.
If eos="unesco", the density is calculated using the UNESCO equation
of state for seawater [1,2], and if eos="gsw", the GSW formulation
[3,4] is used.
References
Fofonoff, P. and R. C. Millard Jr, 1983. Algorithms for
computation of fundamental properties of seawater. Unesco
Technical Papers in Marine Science, 44, 53 pp. (Section 7,
pages 38-40)