Figure 2.17: Mean ice thickness
at places where early cruises were (nearly) collocated with cruises in the 1990s.
Early data (1958 to 1976) are shown by open triangles, and those from the 1990s
by solid squares, both seasonally adjusted to September 15. The small dots show
the original data before the seasonal adjustment. The crossings are grouped into
six regions separated by the solid lines. From Rothrock et al. (1999).