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3500 m, was replaced by a progressive reduction of deep convection
since then, with an 80 ± 10% reduction in GSDW formation during
the 1980's and with convective exchange restricted to < 1000 m by
1993. The dwindling depth and intensity of vertical exchange and an
increasing deep lateral exchange with the Arctic Ocean through Fram
Strait brought a progressive warming, salinification, deoxygenation
and [weak] stratification of Greenland Sea Deep Water.
3. This waxing and waning of Greenland Sea deep convection is attributed two main factors; first to a reduction of local wind stress curl
during the 1980's, so that pre-existing conditions favourable to convection [a strong cyclonic gyre, with surface layer divergence through
Ekman pumping, and a doming ofisopycnals] were replaced by weaker
doming,. a smaller-scale, leaky gyre circulation and weak convection.
Reinforcing this trend, the century-long build-up of wintertime pressure over Greenland, which had resulted in an extreme northerly airflow and record winter cooling over the Nordic seas by the 1960's,
showed an abrupt weakening in the late 1970's and steadily-warming
air temperatures since then have continued the suppression of convective overturn. A reduced sea-ice extent during the 1980's, hence lesser
brine-production, may have been a third contributory factor.
4. A recent deepening of the Eurasian Basin Deep Water layer in the
Greenland Sea, without any associated change in density, is the first
direct evidence that the suppression of convection is being accompanied by some relaxation or collapse of the Greenland Sea dome. This,
rather than any resumption of deep mixing, is the likely cause of the
reported increase in CFC concentrations at all depths to 3000 m between 1981 and 1991.
5. The Deep Water of the Norwegian Sea is composed partly of GSDW
and, until the early 1990's, exhibited a low-amplitude and lagged version of the temperature changes shown by GSDW itself. There was
also an apparent lag with decreasing depth in the Norwegian Sea,
so that the recent abrupt warming appeared first at 2000 m where
the greatest change in the GSDW had been recorded. Since 1990,
as GSDW production dwindled to near-extinction, the NSDW has
ceased to warm further at depth, and there are some signs that the
connecting flow through the Jan Mayen Channel may have reversed.
3500 m, was replaced by a progressive reduction of deep convection
since then, with an 80 ± 10% reduction in GSDW formation during
the 1980's and with convective exchange restricted to < 1000 m by
1993. The dwindling depth and intensity of vertical exchange and an
increasing deep lateral exchange with the Arctic Ocean through Fram
Strait brought a progressive warming, salinification, deoxygenation
and [weak] stratification of Greenland Sea Deep Water.
3. This waxing and waning of Greenland Sea deep convection is attributed two main factors; first to a reduction of local wind stress curl
during the 1980's, so that pre-existing conditions favourable to convection [a strong cyclonic gyre, with surface layer divergence through
Ekman pumping, and a doming ofisopycnals] were replaced by weaker
doming,. a smaller-scale, leaky gyre circulation and weak convection.
Reinforcing this trend, the century-long build-up of wintertime pressure over Greenland, which had resulted in an extreme northerly airflow and record winter cooling over the Nordic seas by the 1960's,
showed an abrupt weakening in the late 1970's and steadily-warming
air temperatures since then have continued the suppression of convective overturn. A reduced sea-ice extent during the 1980's, hence lesser
brine-production, may have been a third contributory factor.
4. A recent deepening of the Eurasian Basin Deep Water layer in the
Greenland Sea, without any associated change in density, is the first
direct evidence that the suppression of convection is being accompanied by some relaxation or collapse of the Greenland Sea dome. This,
rather than any resumption of deep mixing, is the likely cause of the
reported increase in CFC concentrations at all depths to 3000 m between 1981 and 1991.
5. The Deep Water of the Norwegian Sea is composed partly of GSDW
and, until the early 1990's, exhibited a low-amplitude and lagged version of the temperature changes shown by GSDW itself. There was
also an apparent lag with decreasing depth in the Norwegian Sea,
so that the recent abrupt warming appeared first at 2000 m where
the greatest change in the GSDW had been recorded. Since 1990,
as GSDW production dwindled to near-extinction, the NSDW has
ceased to warm further at depth, and there are some signs that the
connecting flow through the Jan Mayen Channel may have reversed.