CDO

I want to select a wedge (a "pizza slice" as one would view it on a spherical globe) from the attached file starting at the south pole, up to about -60S, and between two lines of longitude.

When selecting the area with:
cdo sellonlatbox,50,70,-90,-60 file.nc file2.nc
and viewing the file with ncview, it looks like the longitudes at the pole are not the same as around -60S (as if CDO as simply taken a "visual box" of the original data and not maintained the "50" to "70" lines of longitude with changing latitude).

Thanks,
Oliver