Pacific Westerly Winds Biome
345
edge the velocity core separates before passing north to Taiwan. This separation is the
site of active upwelling from October to January that is apparently unconnected to local
wind forcing.
The Kuroshio is progressively strengthened by lateral entrainment of water from the
subtropical gyre and, within it, the pycnocline slopes upward consistently toward the west.
The main thermocline lies at 75–200 m near the shelf edge at 25
N and at 200–350 m
out over deep water, the surface water mass of the Sea of Japan cooling more strongly in
winter than the main core of the Kuroshio. The main flow is locked to the topography of
the continental edge of the East China Sea, passing landward of the long Ryuku chain of
islands and returning to the open ocean through the Tokara Strait south of Japan (Taft,
1972; Nitani, 1972). Although the main flow continues along the east coast of Japan,
some passes as the Tshushima Current into the Sea of Japan; this flow responds to the
alternating monsoon winds, becoming maximal in summer (Isobe et al., 1994). Okhotsk
Sea water enters the Sea of Japan from the Sakhalin Channel, so that the entire basin
flows cyclonically: warm poleward flow along the Japanese coast and equatorward cold
flow down the Sibero-Korean coast.
Velocity of the Kuroshio flow is topographically intensified north of Taiwan; the
upwelling that is forced by this effect, and is reinforced by the advent of the Northeast
monsoon, will be discussed in the account of the adjacent coastal boundary province
(see CHIN).
Important and well-studied variation occurs in the main stream that flows south of
the Japanese islands. Below southern Honshu (at about 135–140
E) a variety of paths
are taken by the core, principally in two modes: (i) a simple alongshore path flowing
along the shelf edge or (ii) more complex flow, passing around a large cyclonic meander
that extends as much as 500 km offshore. In the second mode, which occurs during
periods of high transport, the return limb of the meander lies along the western side of
the topography of the Izu-Ogasawara Ridge, and the meander itself encloses a cold-core
cyclonic eddy adjacent to the coast (Taft, 1972). Alternation between the two modes
occurs on the decadal scale and has important biological consequences. Since 1960, the
large meander has been established during five periods: 1960–63, 1975–79, 1982–84, 1988,
and 1990. Since 1990, a strong warming trend in autumn-winter SSTs has occurred in
the northern Kuroshio.
Retroflection out across the Pacific finally occurs at about 35
N (Su et al., 1990),
where strongly meandering flow passes northeastward adjacent to cold Oyashio water,
so having a cold wall—like that of the Gulf Stream—on its landward side: this is
the Kuroshio Front (Nagata et al., 1986). The meanders and flow of Kuroshio water
can then be traced eastward into the North Pacific Current as the frontal jet of
the Transition Zone, or the NPTZ Province; the boundary between the Kuroshio
and the NPTZ may conveniently be set at 155
E, above the topography of the
Shatskiy Rise.
The eastward retroflection of the Kuroshio, and its encounter with the cool Oyashio
flow, is a region of great complexity, well described by Kawai (1972). Part of the warm core
(about 20
C) turns offshore near Tokyo and enters a region of meandering interactions.
Thermal fronts between the cool Oyashio and the warm Kuroshio surface water are well
marked and form the origin of the two fronts associated with the oceanic Polar Frontal
Zone as it passes east across the North Pacific.
The Kuroshio, like the Gulf Stream, is a region of anomalously high values for
the kinetic energy contained in the mesoscale eddy field (Dickson, 1983), and this is
undoubtedly the reason for the high variability noted in shipboard measurements of the
chlorophyll field (Taniguchi and Kawamura, 1972). The eddy field of the Kuroshio to
the east of Japan resembles that of the Gulf Stream: cyclonic cold-core eddies are shed
seaward and warm-core anticyclonic eddies landward (Kawai, 1979; Kitano, 1979). Eddies
345
edge the velocity core separates before passing north to Taiwan. This separation is the
site of active upwelling from October to January that is apparently unconnected to local
wind forcing.
The Kuroshio is progressively strengthened by lateral entrainment of water from the
subtropical gyre and, within it, the pycnocline slopes upward consistently toward the west.
The main thermocline lies at 75–200 m near the shelf edge at 25
N and at 200–350 m
out over deep water, the surface water mass of the Sea of Japan cooling more strongly in
winter than the main core of the Kuroshio. The main flow is locked to the topography of
the continental edge of the East China Sea, passing landward of the long Ryuku chain of
islands and returning to the open ocean through the Tokara Strait south of Japan (Taft,
1972; Nitani, 1972). Although the main flow continues along the east coast of Japan,
some passes as the Tshushima Current into the Sea of Japan; this flow responds to the
alternating monsoon winds, becoming maximal in summer (Isobe et al., 1994). Okhotsk
Sea water enters the Sea of Japan from the Sakhalin Channel, so that the entire basin
flows cyclonically: warm poleward flow along the Japanese coast and equatorward cold
flow down the Sibero-Korean coast.
Velocity of the Kuroshio flow is topographically intensified north of Taiwan; the
upwelling that is forced by this effect, and is reinforced by the advent of the Northeast
monsoon, will be discussed in the account of the adjacent coastal boundary province
(see CHIN).
Important and well-studied variation occurs in the main stream that flows south of
the Japanese islands. Below southern Honshu (at about 135–140
E) a variety of paths
are taken by the core, principally in two modes: (i) a simple alongshore path flowing
along the shelf edge or (ii) more complex flow, passing around a large cyclonic meander
that extends as much as 500 km offshore. In the second mode, which occurs during
periods of high transport, the return limb of the meander lies along the western side of
the topography of the Izu-Ogasawara Ridge, and the meander itself encloses a cold-core
cyclonic eddy adjacent to the coast (Taft, 1972). Alternation between the two modes
occurs on the decadal scale and has important biological consequences. Since 1960, the
large meander has been established during five periods: 1960–63, 1975–79, 1982–84, 1988,
and 1990. Since 1990, a strong warming trend in autumn-winter SSTs has occurred in
the northern Kuroshio.
Retroflection out across the Pacific finally occurs at about 35
N (Su et al., 1990),
where strongly meandering flow passes northeastward adjacent to cold Oyashio water,
so having a cold wall—like that of the Gulf Stream—on its landward side: this is
the Kuroshio Front (Nagata et al., 1986). The meanders and flow of Kuroshio water
can then be traced eastward into the North Pacific Current as the frontal jet of
the Transition Zone, or the NPTZ Province; the boundary between the Kuroshio
and the NPTZ may conveniently be set at 155
E, above the topography of the
Shatskiy Rise.
The eastward retroflection of the Kuroshio, and its encounter with the cool Oyashio
flow, is a region of great complexity, well described by Kawai (1972). Part of the warm core
(about 20
C) turns offshore near Tokyo and enters a region of meandering interactions.
Thermal fronts between the cool Oyashio and the warm Kuroshio surface water are well
marked and form the origin of the two fronts associated with the oceanic Polar Frontal
Zone as it passes east across the North Pacific.
The Kuroshio, like the Gulf Stream, is a region of anomalously high values for
the kinetic energy contained in the mesoscale eddy field (Dickson, 1983), and this is
undoubtedly the reason for the high variability noted in shipboard measurements of the
chlorophyll field (Taniguchi and Kawamura, 1972). The eddy field of the Kuroshio to
the east of Japan resembles that of the Gulf Stream: cyclonic cold-core eddies are shed
seaward and warm-core anticyclonic eddies landward (Kawai, 1979; Kitano, 1979). Eddies