GSW-FreePascal is a FreePascal/Lazarus wrapper for GSW-C, which is the C implementation of the Thermodynamic Equation of Seawater 2010 (TEOS-10).
This module is just a wrapper so you have to have a binary version of GSW-C installed on your machine.
There are two ways of getting it:
1). Build it yourself following GSW-C instructions. This way is highly recommended;
2). Use precompiled binaries. This approach is experimental and may not work on your system.
To use the module in your code simply copy 'gibbsseawater.pas' into your project folder and add it to the 'uses' section.
uses GibbsSeaWater;
If you work on Windows just put 'libgswteos-10.dll' next to your executable.
Procedure GSW_test;
Var
sa, ct, t, p: double; //initial data
res1, res2, res3:double; //results
Begin
sa:=36;
ct:=28;
t:= 20;
p:= 1023;
res1:=gsw_adiabatic_lapse_rate_from_ct(sa, ct, p);
res2:=gsw_c_from_sp(sp, t, p);
res3:=gsw_cp_ice(t, p);
writeln(res1+#9+res2+#9+res3);
End;
More information on the functions can be found here.
Comprehensive info on TEOS-10 can be found on the official site and official repository.