function [ppt] = psu2ppt(psu)

% converts salinity from PSU units to PPT
% see:
% http://stommel.tamu.edu/~baum/paleo/ocean/node31.html#PracticalSalinityScale

a = [0.008; -0.1692; 25.3851; 14.0941; -7.0261; 2.7081];
ppt = a(1) + a(2) * psu.^(0.5) + a(3) * psu + a(4) * psu.^(1.5) ...
      + a(5) * psu.^2 + a(6) * psu.^(2.5);