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9. Labrador Sea convection intensified in two main steps, during the early
'70's and from the late '80's onwards. Though the annual changes in
the () - S characteristics of LSW appear to be mutually-compensating
in density over most of the period of record, the excavation of the
cold but saline NADW sublayer during the deepest-reaching convection since 1992 has caused a clear recent increase in LSW density.
A similar increase in density is indicated in the hydrographic record
from the late '20's/early '30's, although at a higher base-temperature
and salinity. Closer inspection of the full record suggests that LSW
density may in fact be a subtly- and continuously-varying function of
windspeed and heat exchange, contrary to the established view that
it is stable in time.
10. Changes in the () - S characteristics of the NADW sublayer of the
Labrador Sea appear to be advectively transferred from source, reflecting changes in the Arctic Intermediate Water that overflows the
Denmark Strait, and/or the near-surface layers of the Irminger Sea
that are entrained as it does so.
11. Using the new dense LSW as a tracer, spreading rates at intermediate depths in the Labrador-Irminger Basin have been estimated at
1-3 cm/s, an order of magnitude greater than published values. The
arrival of LSW vintages from the early '70's in the Rockall Trough in
1990-91 and in the Gulf Stream Recirculation by 1977 suggest lower
long-range spreading rates of around 0.5 cm/s. Salinity, CFC and potential vorticity characteristics suggest that the products of the late'80's convective event have crossed the Mid-Atlantic Ridge and have
reached the eastern boundary in 1994.
12. Thus, coordinated by the scales and configuration of the forcing, we
suggest that convective activity at all three sites evolved over decades
to a long-term extreme state ~ in phase but of differing sign ~ during
the NAO minimum of the 1960's, at which time the ventilation of
the Greenland Sea and Sargasso was at a maximum and that of the
Labrador Sea was tightly capped. Since then all three centres have
evolved rather more rapidly towards their opposite extreme states, in
which convection in the Greenland Sea and Sargasso is suppressed
but vertical exchange in the Labrador Sea is reaching deeper than
previously observed. The local mechanisms by which the atmospheric
9. Labrador Sea convection intensified in two main steps, during the early
'70's and from the late '80's onwards. Though the annual changes in
the () - S characteristics of LSW appear to be mutually-compensating
in density over most of the period of record, the excavation of the
cold but saline NADW sublayer during the deepest-reaching convection since 1992 has caused a clear recent increase in LSW density.
A similar increase in density is indicated in the hydrographic record
from the late '20's/early '30's, although at a higher base-temperature
and salinity. Closer inspection of the full record suggests that LSW
density may in fact be a subtly- and continuously-varying function of
windspeed and heat exchange, contrary to the established view that
it is stable in time.
10. Changes in the () - S characteristics of the NADW sublayer of the
Labrador Sea appear to be advectively transferred from source, reflecting changes in the Arctic Intermediate Water that overflows the
Denmark Strait, and/or the near-surface layers of the Irminger Sea
that are entrained as it does so.
11. Using the new dense LSW as a tracer, spreading rates at intermediate depths in the Labrador-Irminger Basin have been estimated at
1-3 cm/s, an order of magnitude greater than published values. The
arrival of LSW vintages from the early '70's in the Rockall Trough in
1990-91 and in the Gulf Stream Recirculation by 1977 suggest lower
long-range spreading rates of around 0.5 cm/s. Salinity, CFC and potential vorticity characteristics suggest that the products of the late'80's convective event have crossed the Mid-Atlantic Ridge and have
reached the eastern boundary in 1994.
12. Thus, coordinated by the scales and configuration of the forcing, we
suggest that convective activity at all three sites evolved over decades
to a long-term extreme state ~ in phase but of differing sign ~ during
the NAO minimum of the 1960's, at which time the ventilation of
the Greenland Sea and Sargasso was at a maximum and that of the
Labrador Sea was tightly capped. Since then all three centres have
evolved rather more rapidly towards their opposite extreme states, in
which convection in the Greenland Sea and Sargasso is suppressed
but vertical exchange in the Labrador Sea is reaching deeper than
previously observed. The local mechanisms by which the atmospheric