and 40
N.
Östlund and Rooth [1990] examined changes in tritium and
C data mostly in the interior of the North Atlantic. They
interpreted a major increase in decay corrected bomb tritium north
of 40
N to a change in the patterns of deep water injection
sometime after the 1972 GEOSECS survey. This change could also be
interpreted as the ``arrival'' of the major part of the bomb
transient (surface water tritium peaked in 1964, see Jenkins
[1994] below). Based on the observed spatial location of gradients
in both data sets, Östlund and Rooth [1990] found
continued evidence of distinct sub-basin scale recirculations.
Doney and Jenkins [1994] comparison of the GEOSECS and
TTO data sets concentrated on the tritium and 
He distributions,
particularly in the DWBC. Maps of average deep water tritium show
values decreasing significantly south of the Grand Banks. In the
subtropics bomb tritium is confined to the western boundary, and
reaches equatorward to 18
N. The decay corrected tritium
inventory in the North Atlantic more then doubled between 1972 and
1981. In both surveys the partitioning remained similar: about
half of the inventory was in the Labrador Basin, about 30% in the
North American Basin, and 15% in the European Basin, with the
small remaining amount in the North African Basin.
Using the TTO and other data, Doney and Jenkins [1994]
constructed a useful composite DWBC section between the Denmark
Straits and Florida (Figure 4). In the subpolar gyre the LSW is
well ventilated, below this there is a tritium minimum identified
by Swift [1984] as ISOW. In the core of LNADW, the
tritium/
He age increases linearly downstream, the estimated
equatorward velocity is 1.7 cm/s (2.0 cm/s along a constant density
surface). Using a ventilation model, they estimated that the DWBC
exchanges water with interior every 2500-4000 km. Among the
effects of this exchange are relatively rapid ventilation of the
deep Labrador Sea and western subpolar gyre, and a reduction in
equatorward spreading rate.
Doney and Bullister [1992] examined rates of spreading
of water masses in the eastern basin of the North Atlantic using
CFC and hydrographic [ Tsuchiya et al., 1992] data from a
section occupied in 1988 along 20
W. Their data added to the
sparse set of tracer observations there. On the equator they
observed CFC bearing water corresponding to the SLSW similar to
Weiss et al. [1985], and CFC bearing water corresponding to
the LNADW. Compared with LSW, CFC concentrations in Mediterranean
Water (MW) are considerably lower, consistent with what is known
about the MW spreading and entrainment [e.g. Ambar and Howe,
1979] and observations in the Gulf of Cadiz [e.g. Rhein and
Hinrichsen, 1993]. In the deep waters, CFC concentrations in the
ISOW decreased equatorward to blank levels by about 35
N, with
F11/F12 derived ages south of the Rockall Plateau of from twenty to
thirty years.