Pacific Westerly Winds Biome
347
flow east of Hokkaido. Chlorophyll enhancement here is strongly influenced by eddy
vorticity, upwelling along the shelf edge topography, mixing with nutrient-rich coastal
water, and the encounter with Oyashio water (for further discussion of this region,
see Shiomoto, 2000). The edges of warm-core rings are consistently associated with
enhanced chlorophyll and higher-than-background abundance of other pelagic biota
(Yamamoto and Nishizawa, 1986). This often appears also to result from the entrainment of slope-water biota in cold filaments drawn around the individual warm-core
eddies; a typical example of the surface features of this region is that of the MODIS
sea surface chlorophyll and temperature image for April 2004 (see Color plate 15).
Depending on the precise definition of province boundaries, the perturbed region might
be considered as the southwestern extremity of the Western Subarctic Gyre of PSAG,
or as part of the KURO province. Not wishing to be dogmatic, I place it here for
convenience.
There is, of course, some interannual variability in the seasonal cycle and, although
we have rather few years to compare, the integrated KURO province data for both
2001 and 2002 show somewhat stronger chlorophyll maxima than the preceding 3 years.
The strength of the summer DCM varies regionally, with the strongest features between
Taiwan and the south coast of Honshu, where they lie deep (100–150 m), near the bottom
of the euphotic zone, and contain chlorophyll maxima in the range 05–06 mg chl m
−3 .
In this region, daily primary production reaches 04 g C m
−2 day
−1 . Close to the Tokara
Straits themselves, the DCM is generally shallower and may extend to the bottom
over the continental shelf of the East China Sea. In both spring and summer, in
situ observations show that the Kuroshio main flow corresponds with a linear chlorophyll feature, and this is supported by satellite imagery. Chlorophyll sections across
the stream southeast of Honshu in June show that the DCM has higher values within
the axis of flow, and that it lies at a remarkably uniform depth (about 75 m and at the
1% isolume) from the coast to 400–500 km offshore. Predictably, the DCM lies in
water with undetectable nitrate, but immediately above a strong nutricline (Takahashi
et al., 1985).
I have been unable to locate state-of-the-art discussions of the autotrophic cells, and
of their growth and loss functions that produce the effects seen in satellite images: even
recent accounts of the pelagic ecosystem, such as that of Terazaki (1999), recognize
only the diatom-copepod-fish paradigm. This particular study discusses the differential
distribution of diatom species in the cold- and warm-water sectors of the Sea of Japan,
but omits both their seasonal succession and also the relative importance of the pico
and nano fractions compared with the diatom fraction. An earlier study suggested that
about 50% of autotrophic biomass in KURO is represented by <8-m cells (Furuya and
Marumo, 1983).
Terazaki indicates that major species of mesozooplankton resemble those of the open
North Pacific, though the biomass is about one order of magnitude higher than in adjacent
oceanic PSAG province. The copepod fauna is dominated by N. cristatus, N. plumchrus,
E. bungii, M. pacifica, and species of Pseudocalanus, Oithona, and Euchaeta/Pareuchaeta.
These perform seasonal and ontogenetic migrations similar to those described for the
open-ocean provinces of the North Pacific, whereas during the summer they aggregate
at 10–50 m below the surface. Knowledge of their daily production/biomass ratios (0.05
for six large species) is not very helpful. In both coastal and offshore regions of the
Sea of Japan, mesozooplankton biomass (to < 200 m) is maximal in April–May and is
progressively reduced to a midwinter minimum.
The PICES volume mentioned earlier shows unpublished data describing large copepod
winter biomass for each year in the period 1970–2000. One might take this as a proxy for
the general status of the pelagic ecosystem and conclude that a general decline from high
biomass during the period 1976–1994 and the strong recovery to high biomass thereafter
347
flow east of Hokkaido. Chlorophyll enhancement here is strongly influenced by eddy
vorticity, upwelling along the shelf edge topography, mixing with nutrient-rich coastal
water, and the encounter with Oyashio water (for further discussion of this region,
see Shiomoto, 2000). The edges of warm-core rings are consistently associated with
enhanced chlorophyll and higher-than-background abundance of other pelagic biota
(Yamamoto and Nishizawa, 1986). This often appears also to result from the entrainment of slope-water biota in cold filaments drawn around the individual warm-core
eddies; a typical example of the surface features of this region is that of the MODIS
sea surface chlorophyll and temperature image for April 2004 (see Color plate 15).
Depending on the precise definition of province boundaries, the perturbed region might
be considered as the southwestern extremity of the Western Subarctic Gyre of PSAG,
or as part of the KURO province. Not wishing to be dogmatic, I place it here for
convenience.
There is, of course, some interannual variability in the seasonal cycle and, although
we have rather few years to compare, the integrated KURO province data for both
2001 and 2002 show somewhat stronger chlorophyll maxima than the preceding 3 years.
The strength of the summer DCM varies regionally, with the strongest features between
Taiwan and the south coast of Honshu, where they lie deep (100–150 m), near the bottom
of the euphotic zone, and contain chlorophyll maxima in the range 05–06 mg chl m
−3 .
In this region, daily primary production reaches 04 g C m
−2 day
−1 . Close to the Tokara
Straits themselves, the DCM is generally shallower and may extend to the bottom
over the continental shelf of the East China Sea. In both spring and summer, in
situ observations show that the Kuroshio main flow corresponds with a linear chlorophyll feature, and this is supported by satellite imagery. Chlorophyll sections across
the stream southeast of Honshu in June show that the DCM has higher values within
the axis of flow, and that it lies at a remarkably uniform depth (about 75 m and at the
1% isolume) from the coast to 400–500 km offshore. Predictably, the DCM lies in
water with undetectable nitrate, but immediately above a strong nutricline (Takahashi
et al., 1985).
I have been unable to locate state-of-the-art discussions of the autotrophic cells, and
of their growth and loss functions that produce the effects seen in satellite images: even
recent accounts of the pelagic ecosystem, such as that of Terazaki (1999), recognize
only the diatom-copepod-fish paradigm. This particular study discusses the differential
distribution of diatom species in the cold- and warm-water sectors of the Sea of Japan,
but omits both their seasonal succession and also the relative importance of the pico
and nano fractions compared with the diatom fraction. An earlier study suggested that
about 50% of autotrophic biomass in KURO is represented by <8-m cells (Furuya and
Marumo, 1983).
Terazaki indicates that major species of mesozooplankton resemble those of the open
North Pacific, though the biomass is about one order of magnitude higher than in adjacent
oceanic PSAG province. The copepod fauna is dominated by N. cristatus, N. plumchrus,
E. bungii, M. pacifica, and species of Pseudocalanus, Oithona, and Euchaeta/Pareuchaeta.
These perform seasonal and ontogenetic migrations similar to those described for the
open-ocean provinces of the North Pacific, whereas during the summer they aggregate
at 10–50 m below the surface. Knowledge of their daily production/biomass ratios (0.05
for six large species) is not very helpful. In both coastal and offshore regions of the
Sea of Japan, mesozooplankton biomass (to < 200 m) is maximal in April–May and is
progressively reduced to a midwinter minimum.
The PICES volume mentioned earlier shows unpublished data describing large copepod
winter biomass for each year in the period 1970–2000. One might take this as a proxy for
the general status of the pelagic ecosystem and conclude that a general decline from high
biomass during the period 1976–1994 and the strong recovery to high biomass thereafter