function Sc = sc_coeff_he(T,G)

% Schmidt number and gas exchange coefficient for He-4 and He-4
% He-4 data from Wanninkhof, 1992. 
% He-3 Sc based on OCMIP-2 formulation which reduces the He-4 Sc by 15 %, 
% based on the ratio of the reduced masses, which is consistent with helium 
% isotopic fractionation measurements.

% Samar Khatiwala (spk@ldeo.columbia.edu)

if nargin<2 % default is He-4
  ig=1;
else
  switch upper(G)
	case {'HE-3','HE3'}
	  ig=2;
	case {'HE-4','HE4'}
	  ig=1;
	otherwise
	  error('Unknown gas')
  end 
end

Sc = 410.14 - 20.503*T + 0.53175*(T.^2) - 0.0060111*(T.^3);

if ig==2
  Sc=Sc/1.15;
end  
