The MLD fields available are computed from climatological monthly mean profiles of potential temperature and potential density based on three different criteria: a temperature change from the ocean surface of 0.5 degree Celsius, a density change from the ocean surface of 0.125 (sigma units), and a variable density change from the ocean surface corresponding to a temperature change of 0.5 degree Celsius. The MLD based on the variable density criterion is designed to account for the large variability of the coefficient of thermal expansion that characterizes seawater.