water crossing the Indian Ocean to flow south
through the Mozambique Channel, Agulhas Current
and into the South Atlantic. Whether the westward
flow immediately south of Australia is an important,
overlooked element of a global-scale interocean circulation pattern, or more of a regional, Indian
Ocean gyre reaching into the Tasman Sea, is an
important issue to be resolved. The basic question is,
‘Is the South Pacific “climate” imprinted on the
Pacific to Indian flow south of Australia?’
4.7.2 Bering Strait
4.7.2.1 Introduction
The Bering Strait, with a sill depth of 45 m within
Anadry Strait (about 200 km south of the narrowest width of Bering Strait), allows cold, low-salinity
surface waters to flow from the North Pacific to the
Atlantic’s Arctic Sea (Fig. 4.7.1b, see Plate 4.7.1b,
p. 300). While the mass transport of less than 1 Sv
is minor compared with other interocean flows, it is
notable because of the influence of the Bering strait
transport on the Arctic freshwater budget (Aagaard
and Carmack, 1989, 1994; Swift et al., 1997).
North Pacific waters entering the Arctic Sea spreads
within the Arctic upper pycnocline layer into the
Canada Basin. The Bering Strait water eventually is
exported from the Arctic to the northern North
Atlantic Ocean via the Fram Strait and within the
complex channels of the Canadian northwest territory (Rudels et al., 1994; Jones et al., 1998).
4.7.2.2 Transport
A 4-year time series of temperature, salinity and
velocity data across the Bering Strait from 1991 to
1994 is presented by Roach et al. (1995). They
find a mean transport of 0.83 Sv with a weekly
standard deviation of 0.66 Sv. The annual cycle
has a range of 1 Sv, with a maximum in summer,
and a secondary maximum in January. Interannual
variability of 0.5 Sv is observed. The northward
transport of Pacific water is linearly linked to the
meridional wind (transport:1.0690.12 V, where
V:meridional wind in m s
91
). Roach et al. (1995)
find that the salinity of the throughflow is near
32 in autumn and about 34 in the spring, the
difference reflecting summer ice melt and winter ice
formation. Niebauer (1998) shows large changes
in sea-level atmosphere pressure over the North
Pacific as the Aleutian low shifts zonally in response
to El Niño and La Niña phases (further east during
El Niño). Large interannual variability of the transport and properties of the Bering Strait Throughflow may be related to changing sea ice distribution
and wind responding to the shifting Aleutian low.
4.7.2.3 Thermohaline fluxes
Aagaard and Carmack (1989) stress the importance
of salinity to convective overturning within the
Greenland, Iceland, Norwegian and Labrador Seas.
Much of the low-salinity surface water carried into
these seas by the East Greenland Current is derived
from the North Pacific via the Bering Strait. Investigating the freshwater budget for the Arctic Sea
(defined as the region between Fram Strait and
Bering Strait) relative to 34.80, the mean salinity of
the Arctic Sea, they find that the Bering Strait
Throughflow of 0.8 Sv supplies 1670 km
3 yr
91 of
fresh water to the Arctic Sea; if spread evenly over
the Arctic Sea, this amounts to 18 cm yr
91
. This
is the second largest source of fresh water for
the Arctic Sea, the largest being river runoff
(3300 km
3 yr
91
, about 0.13 Sv of fresh water, providing an Arctic freshwater cover of 35 cm yr
91
).
Wijffels et al. (1992) begin their global assessment of oceanic freshwater fluxes with the Bering
Strait, using 0.8 Sv of 32.5 salinity water. In their
analysis ‘… freshwater transport applies to that
part of a seawater flux that is pure water.’ As seawater is roughly 3.5% salt, the freshwater component is 96.5%. Wijffels et al. (1992), using the
Bering Strait flux and the Baumgartner and
Reichel (1975) sea–air freshwater flux values, find
0.75 Sv of fresh water enters the Arctic Sea from
the Pacific. That, with the 0.18 Sv (0.05 Sv more
than the Aagaard and Carmack value) of fresh
water added to the Arctic by excess of runoff and
precipitation minus evaporation, yields 0.93 Sv of
fresh water exiting the Arctic Sea, across the latitude of Iceland.
In summer, when the Bering Strait throughflow
transport is at a maximum, it injects its properties
into the 50–100 m layer of the Arctic Sea, inducing
a weak subsurface temperature maximum. In winter, colder and more saline Bering Strait water
spreads into a deeper Arctic layer, 150–200 m,
producing a temperature minimum (Tomczak and
Godfrey, 1994; Rudels et al., 1996). Cold, lowsalinity Bering Strait water contributing to the
Arctic pycnocline, acts to isolate the warmer
deeper water derived from the Atlantic from the
ice covered surface, reducing vertical heat flux and
SECTION 4 THE GLOBAL FLOW FIELD
306
through the Mozambique Channel, Agulhas Current
and into the South Atlantic. Whether the westward
flow immediately south of Australia is an important,
overlooked element of a global-scale interocean circulation pattern, or more of a regional, Indian
Ocean gyre reaching into the Tasman Sea, is an
important issue to be resolved. The basic question is,
‘Is the South Pacific “climate” imprinted on the
Pacific to Indian flow south of Australia?’
4.7.2 Bering Strait
4.7.2.1 Introduction
The Bering Strait, with a sill depth of 45 m within
Anadry Strait (about 200 km south of the narrowest width of Bering Strait), allows cold, low-salinity
surface waters to flow from the North Pacific to the
Atlantic’s Arctic Sea (Fig. 4.7.1b, see Plate 4.7.1b,
p. 300). While the mass transport of less than 1 Sv
is minor compared with other interocean flows, it is
notable because of the influence of the Bering strait
transport on the Arctic freshwater budget (Aagaard
and Carmack, 1989, 1994; Swift et al., 1997).
North Pacific waters entering the Arctic Sea spreads
within the Arctic upper pycnocline layer into the
Canada Basin. The Bering Strait water eventually is
exported from the Arctic to the northern North
Atlantic Ocean via the Fram Strait and within the
complex channels of the Canadian northwest territory (Rudels et al., 1994; Jones et al., 1998).
4.7.2.2 Transport
A 4-year time series of temperature, salinity and
velocity data across the Bering Strait from 1991 to
1994 is presented by Roach et al. (1995). They
find a mean transport of 0.83 Sv with a weekly
standard deviation of 0.66 Sv. The annual cycle
has a range of 1 Sv, with a maximum in summer,
and a secondary maximum in January. Interannual
variability of 0.5 Sv is observed. The northward
transport of Pacific water is linearly linked to the
meridional wind (transport:1.0690.12 V, where
V:meridional wind in m s
91
). Roach et al. (1995)
find that the salinity of the throughflow is near
32 in autumn and about 34 in the spring, the
difference reflecting summer ice melt and winter ice
formation. Niebauer (1998) shows large changes
in sea-level atmosphere pressure over the North
Pacific as the Aleutian low shifts zonally in response
to El Niño and La Niña phases (further east during
El Niño). Large interannual variability of the transport and properties of the Bering Strait Throughflow may be related to changing sea ice distribution
and wind responding to the shifting Aleutian low.
4.7.2.3 Thermohaline fluxes
Aagaard and Carmack (1989) stress the importance
of salinity to convective overturning within the
Greenland, Iceland, Norwegian and Labrador Seas.
Much of the low-salinity surface water carried into
these seas by the East Greenland Current is derived
from the North Pacific via the Bering Strait. Investigating the freshwater budget for the Arctic Sea
(defined as the region between Fram Strait and
Bering Strait) relative to 34.80, the mean salinity of
the Arctic Sea, they find that the Bering Strait
Throughflow of 0.8 Sv supplies 1670 km
3 yr
91 of
fresh water to the Arctic Sea; if spread evenly over
the Arctic Sea, this amounts to 18 cm yr
91
. This
is the second largest source of fresh water for
the Arctic Sea, the largest being river runoff
(3300 km
3 yr
91
, about 0.13 Sv of fresh water, providing an Arctic freshwater cover of 35 cm yr
91
).
Wijffels et al. (1992) begin their global assessment of oceanic freshwater fluxes with the Bering
Strait, using 0.8 Sv of 32.5 salinity water. In their
analysis ‘… freshwater transport applies to that
part of a seawater flux that is pure water.’ As seawater is roughly 3.5% salt, the freshwater component is 96.5%. Wijffels et al. (1992), using the
Bering Strait flux and the Baumgartner and
Reichel (1975) sea–air freshwater flux values, find
0.75 Sv of fresh water enters the Arctic Sea from
the Pacific. That, with the 0.18 Sv (0.05 Sv more
than the Aagaard and Carmack value) of fresh
water added to the Arctic by excess of runoff and
precipitation minus evaporation, yields 0.93 Sv of
fresh water exiting the Arctic Sea, across the latitude of Iceland.
In summer, when the Bering Strait throughflow
transport is at a maximum, it injects its properties
into the 50–100 m layer of the Arctic Sea, inducing
a weak subsurface temperature maximum. In winter, colder and more saline Bering Strait water
spreads into a deeper Arctic layer, 150–200 m,
producing a temperature minimum (Tomczak and
Godfrey, 1994; Rudels et al., 1996). Cold, lowsalinity Bering Strait water contributing to the
Arctic pycnocline, acts to isolate the warmer
deeper water derived from the Atlantic from the
ice covered surface, reducing vertical heat flux and
SECTION 4 THE GLOBAL FLOW FIELD
306