223
[Figure 10, from Osterhus and Gammelsrod, in press]. Since the maximum
T and S change in the deep Greenland Sea was centred on 2000-2500 m
depth, [see Aagaard, Fahrbach, Meincke and Swift, 1991, inset to their
Figure 8], and since the Jan Mayen Channel has a sill depth [~ 2000m]
which permits exchange at this level, it is perhaps also unsurprising that
this was the depth first affected in the Norwegian Sea. Figure 11, also from
Osterhus and Gammelsrod, neatly captures the depth-lag of the ascending
signal in showing that the end of the cooling and beginning of the warming
at MIKE took place in the early-to-mid 1980's at 2000 m, but in the late
'80's at 1500 m and around 1990 at 1200 m. There seems little doubt from
the precipitous nature of the change that this is the same feature at all
these depths or that it represents a remote response to the equally radical
warming and salinification of deep waters in the central Greenland Sea.
[The salinity data-set from MIKE is not adequate to comment on whether
a similar salinification affected the NSDW].
What is unexpected in the deep record from OWS M is the levelling-off
of warming which appears to have taken place at 2000 m since 1990, [not
yet evident at shallower depths], despite the continuation of warming in its
supposed source in the Greenland Sea. Though the data are far from conclusive, the working hypothesis put forward by Osterhus and Gammelsrod
[Osterhus, pers comm] is that the virtual cessation of GSDW production
may have been reflected in a reversal of flow in the Jan Mayen Channel
since that date, effectively cutting-off the deep Norwegian Sea from the
influence of GSDW and its changes. The available evidence is summarised
in Figure 12 a,b showing that long-term, near-bottom current measurements close to the sill of the Jan Mayen Channel in April-November 1981
[Saelen, 1988] and from September 1983-July 1984 were all strongly and
constantly eastward, while measurements at the same depth and site in
November 1992-July 1993 showed a sluggish westward flow [Osterhus and
Gammelsrod, op cit]. Further measurements to confirm this change are
clearly necessary and are planned.
[Figure 10, from Osterhus and Gammelsrod, in press]. Since the maximum
T and S change in the deep Greenland Sea was centred on 2000-2500 m
depth, [see Aagaard, Fahrbach, Meincke and Swift, 1991, inset to their
Figure 8], and since the Jan Mayen Channel has a sill depth [~ 2000m]
which permits exchange at this level, it is perhaps also unsurprising that
this was the depth first affected in the Norwegian Sea. Figure 11, also from
Osterhus and Gammelsrod, neatly captures the depth-lag of the ascending
signal in showing that the end of the cooling and beginning of the warming
at MIKE took place in the early-to-mid 1980's at 2000 m, but in the late
'80's at 1500 m and around 1990 at 1200 m. There seems little doubt from
the precipitous nature of the change that this is the same feature at all
these depths or that it represents a remote response to the equally radical
warming and salinification of deep waters in the central Greenland Sea.
[The salinity data-set from MIKE is not adequate to comment on whether
a similar salinification affected the NSDW].
What is unexpected in the deep record from OWS M is the levelling-off
of warming which appears to have taken place at 2000 m since 1990, [not
yet evident at shallower depths], despite the continuation of warming in its
supposed source in the Greenland Sea. Though the data are far from conclusive, the working hypothesis put forward by Osterhus and Gammelsrod
[Osterhus, pers comm] is that the virtual cessation of GSDW production
may have been reflected in a reversal of flow in the Jan Mayen Channel
since that date, effectively cutting-off the deep Norwegian Sea from the
influence of GSDW and its changes. The available evidence is summarised
in Figure 12 a,b showing that long-term, near-bottom current measurements close to the sill of the Jan Mayen Channel in April-November 1981
[Saelen, 1988] and from September 1983-July 1984 were all strongly and
constantly eastward, while measurements at the same depth and site in
November 1992-July 1993 showed a sluggish westward flow [Osterhus and
Gammelsrod, op cit]. Further measurements to confirm this change are
clearly necessary and are planned.