represents one of the longest float trajectories
of the 171 floats studied. It spent more than five years
in the centre of the subtropical gyre. During the first three
years of its life the AAIW properties experienced by the float
were very different from the AAIW properties of the WOA
field. The fact that from day 1300 onward both AAIW properties
show excellent agreement suggests very strongly that
the float retained its calibration through the entire five year
period. The reasons for the departure of the observed AAIW
salinity minimum from the WOA field are difficult to establish.
It could be an indication of a large scale shift of the
mean field, but it could also indicate uncertainty in theWOA
field itself; the data distribution on which the WOA field is
based has some significant holes in the region (Fig. 6). The
Argo team assessed float 39047 as corrupted (Wijffels, personal
communication). The argument is discussed in more
detail in the Appendix. In the present context the float serves
to demonstrate the possible validity and significance of elevated
standard deviations.