Density values calculation:

Density is presented as [(density(t,s,z) - 1000] kg/m³ (sigma), density at given temperature (t), salinity (s), depth (z). Please note that before Oct. 4, standard name in the netCDF files and in the figure captions was sigma_t, which was incorrect as sigma_t is [(density(t,s,0)-1000] kg/m³, density at atmospheric pressure. Standard names have been corrected.

Density values were calculated from concurrent in situ observations of temperature and salinity. The pressure value was also in situ, derived from depth measurement when not observed directly, following the algorithm outlined in Processing of Oceanographic Station Data (UNESCO, 1991,). The Equation of State 1980 (EOS-80) algorithm as found in Algorithms for computation of fundamental properties of seawater (UNESCO, 1983,) was used to compute density from temperature, salinity, pressure.

Density values were then interpolated to standard depth levels and objectively analyzed in the same manner as temperature and salinity in the World Ocean Atlas 2013 (Locarnini et al, 2013; Zweng et al, 2013).

Conductivity values calculation:

Please cite conductivity data using: Tyler, R. H., T. P. Boyer, T Minami, M. M. Zweng, J. R. Reagan, 2017 Electric conductivity of the global ocean submitted to Earth, Planets, and Space.

Conductivity was back calculated from observed temperature and salinity values from the World Ocean Database. Pressure, when not a recorded variable, was calculated from depth following the algorithm outlined in Processing of Oceanographic Station Data (UNESCO, 1991).

Ocean profiles were used only back to 1981 to ensure that most, if not all salinity data were recorded using the Practical Salinity Scale 1978 (PSS-78).

Back-calculation of conductivity was done using routine teos_sal_to_cond from the Gibbs SeaWater (GSW) Oceanographic Toolbox of The Equation of State 2010 (TEOS-10).

Conductivity values were then interpolated to standard depth levels and objectively analyzed in the same manner as temperature and salinity in the World Ocean Atlas 2013 (Locarnini et al, 2013; Zweng et al, 2013.