To obtain a reference time series representative of smooth diffusive evolution of the salinity minimum, the AAIW salinity minimum along the track of each float was reconstructed from the World Ocean Atlas (WOA; Conkright et al., 2002). The WOA data were assigned to the centre of their respective 1◦ square for this purpose, and the salinity profile along the float track was determined by spatial linear interpolation of the annual mean WOA field. Temporal interpolation using seasonal WOA data was not considered appropriate, the assumption being that the AAIW seen by the float was water that moved more or less with the float and was out of reach of the seasonal changes that operate during the AAIW formation process.