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Comparisons of the climatologies in 6-S space for two transects: across the Gulf Stream 
and across the Antarctic Circumpolar Current are presented in Fig. 16. Both regions are 
characterised by strong lateral property gradients, where isobaric/isopycnal averaging 
effects are supposed to be especially pronounced. Indeed, our comparison reveals artificial 
water masses in the WOA01 climatology. In the Gulf-Stream area within the potential 
temperature range 6-15 degrees an artificial water mass is observed with salinities up to 0.1 
greater, compared with observations. In the ACC region the WOA01 climatology is also 
characterised by an anomalous water mass between ~2.5 and 6 °C, with salinity exceeding 
observed values by 0.05-0.1. 
An overview of these effects is given in Fig. 17, where temperature and salinity differences 
between the WOA01 and WGHC climatologies are shown for the level 500 meters. A 
number of pronounced geographical patterns are observed, with the largest anomalies 
coinciding with such current systems, like Gulf-Stream, Kuroshio, Agulhas, and the ACC. It 
should be kept in mind, however, that the WOA01 input data are not identical to those used 
in our calculations. Therefore we repeated the calculations using the same optimal 
interpolation algorithm and the same input data but on isobaric surfaces. The result of the 
comparison allows to conclude, that most of the difference patterns of the Fig.16 are really 
due to the effects of isobaric averaging of the data in WOA01 climatology. 
Fig. 18: Depth-bin-averaged absolute deviation of WOA01 and WGHC 
climatologies from the high-quality reference profile dataset. 
Ratio is defined as |(f 0 bs-fwoAoi)|/|(fobs-fwGHc)l- 
A comparison was done between the global reference (observed) data set and both 
climatologies. Ratios of absolute differences |(T obs -T WO Aoi)|/|(Tobs-TwGHc)| and |(S obs - 
SwoA0i)|/|(Sobs-SwGHc)l were computed for each observed T,S-pair. All depth-bin averaged 
ratios are greater than unit (Fig. 18), indicating the WGHC climatology being closer to the 
high-quality data compared with the WOA01 climatology. The largest differences are 
observed in the deep water below 2000 m, where both temperature and salinity ratios 
exceed 1.5. Ratios of absolute deviations from observations averaged within 1x1 degree 
boxes and within the layer 250-500 meters are shown in Fig.19 and demonstrate a generally 
much better agreement between the original observations and optimally interpolated fields 
for the WGHC climatology.