Institution

145
bottle spacing. An example is the IGY temperature section at
80N (Fuglister, 1960, p. 29). The region of increased
gradient is considered to be the transition between AABW and
the overlying NADW. As mentioned earlier, it is in this
temperature interval that marked indications of increased
salinity first appear in AABW as it penetrates toward the
north.
Recent STD (salinity/temperature/depth) observations
(Amos, Gordon, and Schneider, 1971) indicate that the transi-
tion may be more abrupt than the Nansen bottles show. Their
STD traces recorded changes of 0.02 to 0.04°e occurring over
intervals of less than 20 m at about 1.8°e, but they argue
that the gradient layer is not a transition between AABW and
NADW because some i nfl uence of AABW can be found at sha 11 ower
depths. Although the AABW andNAOW may influence each other
outside the 1.6° to 1.8°e interval in this part of the ocean,
the influence is probably too small to discern with existing
techniques, and the waters above and below the transition
region should be considered as two distinct water masses.
The e/S envelope of all the hydrographic observations
deeper than 4300 m 1 i es on the curve of Worthi ngton and
Me tc a 1 f (i 9 6 1) for the we s t ern No r t h At 1 an tic. A 1 tho ugh
generally colder and fresher, it overlaps the envelope of
e/S values associated with the Western Boundary Undercurrent
up to 1.930e (Fig. 6.5).
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