The effect of seasonal differences in AT data on the
derived AT relationships was also addressed by comparing AT
values predicted from the relationships in Table 1 with AT
measurements which are not included in the data set. The
mean difference of 1.2 ± 7.8 mmol kg1 (1s) indicates that
the derived AT relationships can be used to predict seasonal
extrapolation of surface AT. Some differences are found
locally (Figure 2b), but these are still close to uncertainties
of our AT relationships (see the fifth column in Table 1).