247
4.5 Time dependence in the advective sublayer at OWS BRAVO
Lazier [1988] and Lazier and Gershey, [1991] address the issue of timedependence in the bottom-most layers of the Labrador Sea and its causes.
Below the depth of even the recent record convection this sublayer of North
Atlantic Deep Water must owe the largest part of its T and S variability
to changes in its source areas, transferred by lateral advection. Though
NADW has various constituents, the most likely source-water suggested by
Lazier is Arctic Intermediate Water from the Iceland-Greenland Sea which
overspills the Greenland-Scotland Ridge via the Denmark Strait. Dickson
and Brown [1994], however, show that this water entrains an equal volume
of resident water from the upper layers of the Irminger Sea as it descends
along the Greenland Slope, making this another possible source of change.
Lazier estimates the transit time from overflow to BRAVO to be around
100 days. Except as a recent source of change in the LSW itself, the deepest
layers have little relevance here, but it is perhaps worth noting [Figure 29]
that the variability in the deepest layers at BRAVO [8 at 0'2 = 37.16kglm 3 ;
from Lazier and Gershey, 1991] bears a closer similarity to the temperature
anomaly at 0-200 m in the Irminger component of the Labrador Current,
[Borovkov and Tevs, 1991] than anything in the superjacent watercolumn.
4.6 The spreading of Labrador Sea Water
As was the case with the GSA signal, the varying characteristics of LSW
provide us with a valuable [perhaps the only] direct means of assessing
spreading rates and pathways at the intermediate depths occupied by this
watermass. Spreading rates may of course vary from one part of the North
Atlantic to another:
(i) The F IS METEOR cruise in November-December 1994 provided
spectacular information on spreading rates within the Labrador-Irminger
Basin itself. In Figure 30, Lazier, Rhein, Sy and Meincke [pers comm.]
demonstrate what is unambiguously the same anomalous increase in density at intermediate depths in the Irminger Sea as Lazier showed for the
LSW core at OWS BRAVO in 1991-94. Strictly, it is not known whether
the dense water found in the Irminger Sea in November 1994 is the counterpart of the anomalously dense water encountered in the Labrador Sea
in the surveys of March 1993 or March 1994. Lazier et al conclude that it
is "very likely" the latter, but in either case the spreading rate indicated
4.5 Time dependence in the advective sublayer at OWS BRAVO
Lazier [1988] and Lazier and Gershey, [1991] address the issue of timedependence in the bottom-most layers of the Labrador Sea and its causes.
Below the depth of even the recent record convection this sublayer of North
Atlantic Deep Water must owe the largest part of its T and S variability
to changes in its source areas, transferred by lateral advection. Though
NADW has various constituents, the most likely source-water suggested by
Lazier is Arctic Intermediate Water from the Iceland-Greenland Sea which
overspills the Greenland-Scotland Ridge via the Denmark Strait. Dickson
and Brown [1994], however, show that this water entrains an equal volume
of resident water from the upper layers of the Irminger Sea as it descends
along the Greenland Slope, making this another possible source of change.
Lazier estimates the transit time from overflow to BRAVO to be around
100 days. Except as a recent source of change in the LSW itself, the deepest
layers have little relevance here, but it is perhaps worth noting [Figure 29]
that the variability in the deepest layers at BRAVO [8 at 0'2 = 37.16kglm 3 ;
from Lazier and Gershey, 1991] bears a closer similarity to the temperature
anomaly at 0-200 m in the Irminger component of the Labrador Current,
[Borovkov and Tevs, 1991] than anything in the superjacent watercolumn.
4.6 The spreading of Labrador Sea Water
As was the case with the GSA signal, the varying characteristics of LSW
provide us with a valuable [perhaps the only] direct means of assessing
spreading rates and pathways at the intermediate depths occupied by this
watermass. Spreading rates may of course vary from one part of the North
Atlantic to another:
(i) The F IS METEOR cruise in November-December 1994 provided
spectacular information on spreading rates within the Labrador-Irminger
Basin itself. In Figure 30, Lazier, Rhein, Sy and Meincke [pers comm.]
demonstrate what is unambiguously the same anomalous increase in density at intermediate depths in the Irminger Sea as Lazier showed for the
LSW core at OWS BRAVO in 1991-94. Strictly, it is not known whether
the dense water found in the Irminger Sea in November 1994 is the counterpart of the anomalously dense water encountered in the Labrador Sea
in the surveys of March 1993 or March 1994. Lazier et al conclude that it
is "very likely" the latter, but in either case the spreading rate indicated