346
Chapter 11: The Pacific Ocean
of both signs then propagate contrary to the direction of the current, for periods of up
to several months. Warm rings form mainly in the transition area between the mean
positions of the Oyashio and Kuroshio Fronts and about 120 km to the east of Hokkaido.
The perturbed area between the cold and warm currents is rich in mesoscale features,
including not only eddies but also warm streamers and filaments carried around cold
eddies and secondary fronts (Kawai and Saitoh, 1986) and cold filaments carried around
warm-core eddies (Sugimoto and Tameishi, 1992). Ephemeral episodes of warm water
and strong currents in inshore waters and even bays along the south coast of Japan reflect
the incidence of warm-core eddies encountering the coastline. These Kyucho events are
therefore the equivalent of the irruptions of warm water at the Nova Scotia coast when
a Gulf Stream eddy founders on the shelf.
Vertical structure of the water column as a response to heat exchange and wind
mixing differs significantly along the course of the Kuroshio as atmospheric conditions
and irradiance respond to latitude. Stratification is more permanent at the root of the
Kuroshio and winter mixing to ∼100 m is more sustained in the northern regions, near
the Japanese islands. As in other coastal boundary currents, the summer pycnocline—and,
hence, the DCM—slopes upward toward the coast.
Regional Response of the Pelagic Ecosystem
Because of the great latitudinal extent of this province, it really comprises two regimes,
here making a marriage of convenience: (i) one that is tropical, from 10
N to 25
N,
having conditions very similar to the WARM Province, and (ii) another, from Taiwan
northward, having a temperate, winter-mixing regime. Compared with available oceanographic analyses and with what is known of pelagic fisheries ecology (tuna, sardines,
saury, etc.) there appear to be few modern studies of the primary production and
consumption regimes. Most of what is available refers to the region north of Taiwan;
therefore, for the southern region, the “beginning of the Kuroshio” of Japanese oceanographers, I can do no more than refer the reader to my discussion of production in
the adjacent province, seaward of the Kuroshio itself (see NPTG, later). However, it
is perhaps noteworthy that the serial satellite images indicate that productivity in the
Kuroshio south of Taiwan exhibits no significant seasonality—a scan of the MODIS 2001
images, for instance, shows persistent oligotrophic conditions in deep water beyond the
shelf break.
In the extra-tropical Kuroshio, there is a clear seasonal cycle in the mixed-layer
depth (summer, 15–25 m; winter, 80–120 m) and because there is some information on
the presence and differentiation of a DCM during summer, we expect a spring bloom
and summer oligotrophy sequence to be widespread. The northern Kuroshio-Oyashio
interaction region, east of Japan, is known to have strong seasonal algal blooms, though
these are more restricted spatially than those of the North Atlantic, with regions of higher
production values lying adjacent to the coastlines (Saijo et al., 1970). Spring and autumn
blooms were described in the central Sea of Japan by Nagata (1998).
The evidence of the serial chlorophyll images from SeaWiFS and MODIS is quite
clear. The seasonal chlorophyll cycle is bimodal: a spring bloom does occur in KURO,
both in the Sea of Japan and in the Pacific, everywhere north of Taiwan so that peak
biomass is achieved in April, followed by a summer oligotrophic period from early June
to September. Chlorophyll accumulates progressively during the last 3 months of the
year only to decline again to an annual minimum in February. The spring bloom is
initially strongest in the eastern half of the Sea of Japan and shifts progressively toward
the north; maximum chlorophyll accumulation (<8–10 mg chl m
−3 ) occurs in the “perturbed region” lying between the Kuroshio retroflection at 35–36
N and the Oyashio
Chapter 11: The Pacific Ocean
of both signs then propagate contrary to the direction of the current, for periods of up
to several months. Warm rings form mainly in the transition area between the mean
positions of the Oyashio and Kuroshio Fronts and about 120 km to the east of Hokkaido.
The perturbed area between the cold and warm currents is rich in mesoscale features,
including not only eddies but also warm streamers and filaments carried around cold
eddies and secondary fronts (Kawai and Saitoh, 1986) and cold filaments carried around
warm-core eddies (Sugimoto and Tameishi, 1992). Ephemeral episodes of warm water
and strong currents in inshore waters and even bays along the south coast of Japan reflect
the incidence of warm-core eddies encountering the coastline. These Kyucho events are
therefore the equivalent of the irruptions of warm water at the Nova Scotia coast when
a Gulf Stream eddy founders on the shelf.
Vertical structure of the water column as a response to heat exchange and wind
mixing differs significantly along the course of the Kuroshio as atmospheric conditions
and irradiance respond to latitude. Stratification is more permanent at the root of the
Kuroshio and winter mixing to ∼100 m is more sustained in the northern regions, near
the Japanese islands. As in other coastal boundary currents, the summer pycnocline—and,
hence, the DCM—slopes upward toward the coast.
Regional Response of the Pelagic Ecosystem
Because of the great latitudinal extent of this province, it really comprises two regimes,
here making a marriage of convenience: (i) one that is tropical, from 10
N to 25
N,
having conditions very similar to the WARM Province, and (ii) another, from Taiwan
northward, having a temperate, winter-mixing regime. Compared with available oceanographic analyses and with what is known of pelagic fisheries ecology (tuna, sardines,
saury, etc.) there appear to be few modern studies of the primary production and
consumption regimes. Most of what is available refers to the region north of Taiwan;
therefore, for the southern region, the “beginning of the Kuroshio” of Japanese oceanographers, I can do no more than refer the reader to my discussion of production in
the adjacent province, seaward of the Kuroshio itself (see NPTG, later). However, it
is perhaps noteworthy that the serial satellite images indicate that productivity in the
Kuroshio south of Taiwan exhibits no significant seasonality—a scan of the MODIS 2001
images, for instance, shows persistent oligotrophic conditions in deep water beyond the
shelf break.
In the extra-tropical Kuroshio, there is a clear seasonal cycle in the mixed-layer
depth (summer, 15–25 m; winter, 80–120 m) and because there is some information on
the presence and differentiation of a DCM during summer, we expect a spring bloom
and summer oligotrophy sequence to be widespread. The northern Kuroshio-Oyashio
interaction region, east of Japan, is known to have strong seasonal algal blooms, though
these are more restricted spatially than those of the North Atlantic, with regions of higher
production values lying adjacent to the coastlines (Saijo et al., 1970). Spring and autumn
blooms were described in the central Sea of Japan by Nagata (1998).
The evidence of the serial chlorophyll images from SeaWiFS and MODIS is quite
clear. The seasonal chlorophyll cycle is bimodal: a spring bloom does occur in KURO,
both in the Sea of Japan and in the Pacific, everywhere north of Taiwan so that peak
biomass is achieved in April, followed by a summer oligotrophic period from early June
to September. Chlorophyll accumulates progressively during the last 3 months of the
year only to decline again to an annual minimum in February. The spring bloom is
initially strongest in the eastern half of the Sea of Japan and shifts progressively toward
the north; maximum chlorophyll accumulation (<8–10 mg chl m
−3 ) occurs in the “perturbed region” lying between the Kuroshio retroflection at 35–36
N and the Oyashio