Smethie [1993] showed that the structure and continuity
of the DWBC extends northward to the Grand Banks (Figure 3b). The
CFCs and hydrographic data were collected along four sections
normal to the continental slope in 1983 and three sections in 1986.
The basic structure of two CFC maxima cores was observed in all
sections. New information comes from CFC derived ages for the
DWBC. Between 44
and 33
N, the ages increase from
eleven to eighteen years for the shallow core, and from twelve to
twenty years for the deep core. For the deep core, a
reconstruction of CFCs in the source components of the LNADW is
used to estimate that 80% of the CFC burden in the mid-1980s is
from the DSOW. Extensions of the sections up to 1300 km into the
interior, provided significant new detail about the circulation
adjacent to the DWBC. Maps of the LNADW showed the high CFC water
from the DWBC spreading into the interior in the Northern
Recirculation Gyre [ Hogg et al., 1986]. Smethie [1993]
observed that the CFC concentrations in the SLSW do not decrease
monotonically from the boundary. Multiple maxima suggested that
there are other processes, in addition to mixing, that transport
the high CFC water to the interior.
Below the LNADW (>1.8
C), Smethie [1993]
described a mixture of the NADW and AABW, which has an inverse
correlation between tracer and silica concentrations [e.g. Top
et al., 1987]. North of the New England Seamount chain, high
silica/low CFC patches are remnants of the AABW. In contrast, at
some stations along the bottom, there are high CFC/low silica
patches (Figure 3b). He estimated that the high CFC/low silica
patches have a slightly greater fraction of the DSOW than the GFZW.
Smethie concluded that this high CFC bottom water is flowing
equatorward offshore and parallel to the DWBC.