Pacific Westerly Winds Biome
337
approximately tracks the light field, but the maximum rate occurs prior to midsummer,
perhaps due to nutrient limitation, and the vernal rate increase is delayed until Z m
begins to shoal in March. Accumulation is coincident with the rate increase in P, and
decline is coincident with the decline in P through June–August. In September–October,
accumulation is renewed and quickly reaches its annual maximum, values remaining
high throughout winter in open water, perhaps representing sediments suspended during
the period of deepening of mixed-layer depth. Renewed accumulation in September is
consistent with the decrease in near-surface copepod biomass as the migrant copepods
descend to overwintering depths.
Pacific Westerly Winds Biome
Pacific Subarctic Gyres Province, East and West
(PSAG)
Extent of the Province
This is a rather large province that should perhaps be partitioned zonally; nevertheless,
in the first edition of this work it was thought better to treat it holistically because of
a dearth of sufficient information to support a partition. Since then, however, we have
access to the Canadian JGOFS studies in the NE subarctic gyre and also to the results
of the JGOFS North Pacific Process Study at Station KNOT in the western gyre. These
new studies will enable us to discuss the undoubted differences in the ecology of the two
parts of this province. Despite this, I still prefer not to partition the gyre formally, so as
to emphasize similarities rather than differences.
To the east and north, PSAG is enclosed by the offshore boundaries of the ALSK
coastal province, and to the north and west by the boundary of BERS along the line of
the Aleutian and Commander Islands, then south along the edge of the East Kamchatka
Current, and finally along the Kuril Islands shelf to the eastern cape of Hokkaido. To the
south, I have taken the divergence of surface flow along about 45
N (Uda, 1963; Ware
and McFarlane, 1989), where North Pacific Current and West Wind Drift waters diverge.
The boundary between the larger eastern and the smaller western subarctic gyres lies to
the south of the westernmost group of Aleutian Islands.
Defining Characteristics of Regional Oceanography
The subarctic (or subpolar) gyral circulation of the Pacific Ocean—Subarctic Current,
Alaska Stream, and East Kamchatka Current—includes the partially isolated Alaskan and
Western Subarctic gyres. This circulation loses some water to the Bering Sea, but the
principal loss is into the California Current, because influx from the West Wind Drift
cannot be balanced against the loss term without consideration of the entrainment of
subhalocline water into the surface layer. This has significance for the ecology of the
province through the continual supply of deep nutrients to the photic zone. These topics
and others were reviewed in three now-classical regional studies: Dodimead et al. (1967),
Uda (1963), and Favorite et al. (1976).
The eastern, Alaskan gyre has long been the site of intensive studies at Ocean Weather
Station P (OWS P) at 50
N 145
W, whereas the western gyre is less well known. The
Alaskan gyre forms an elongated (SW-NE) cyclonic dome in the halocline, shoaling to
75 m at the center. The dome, which is axial to circulation, can be identified by a surface
salinity maximum in the range 32.8–33.0%. Seasonal changes in the depth of the surface
layer of low-salinity water are slight, and it is effectively isolated from deep water by
the permanent halocline at 100–150 m. Changes in SST lag heat input at the surface by
337
approximately tracks the light field, but the maximum rate occurs prior to midsummer,
perhaps due to nutrient limitation, and the vernal rate increase is delayed until Z m
begins to shoal in March. Accumulation is coincident with the rate increase in P, and
decline is coincident with the decline in P through June–August. In September–October,
accumulation is renewed and quickly reaches its annual maximum, values remaining
high throughout winter in open water, perhaps representing sediments suspended during
the period of deepening of mixed-layer depth. Renewed accumulation in September is
consistent with the decrease in near-surface copepod biomass as the migrant copepods
descend to overwintering depths.
Pacific Westerly Winds Biome
Pacific Subarctic Gyres Province, East and West
(PSAG)
Extent of the Province
This is a rather large province that should perhaps be partitioned zonally; nevertheless,
in the first edition of this work it was thought better to treat it holistically because of
a dearth of sufficient information to support a partition. Since then, however, we have
access to the Canadian JGOFS studies in the NE subarctic gyre and also to the results
of the JGOFS North Pacific Process Study at Station KNOT in the western gyre. These
new studies will enable us to discuss the undoubted differences in the ecology of the two
parts of this province. Despite this, I still prefer not to partition the gyre formally, so as
to emphasize similarities rather than differences.
To the east and north, PSAG is enclosed by the offshore boundaries of the ALSK
coastal province, and to the north and west by the boundary of BERS along the line of
the Aleutian and Commander Islands, then south along the edge of the East Kamchatka
Current, and finally along the Kuril Islands shelf to the eastern cape of Hokkaido. To the
south, I have taken the divergence of surface flow along about 45
N (Uda, 1963; Ware
and McFarlane, 1989), where North Pacific Current and West Wind Drift waters diverge.
The boundary between the larger eastern and the smaller western subarctic gyres lies to
the south of the westernmost group of Aleutian Islands.
Defining Characteristics of Regional Oceanography
The subarctic (or subpolar) gyral circulation of the Pacific Ocean—Subarctic Current,
Alaska Stream, and East Kamchatka Current—includes the partially isolated Alaskan and
Western Subarctic gyres. This circulation loses some water to the Bering Sea, but the
principal loss is into the California Current, because influx from the West Wind Drift
cannot be balanced against the loss term without consideration of the entrainment of
subhalocline water into the surface layer. This has significance for the ecology of the
province through the continual supply of deep nutrients to the photic zone. These topics
and others were reviewed in three now-classical regional studies: Dodimead et al. (1967),
Uda (1963), and Favorite et al. (1976).
The eastern, Alaskan gyre has long been the site of intensive studies at Ocean Weather
Station P (OWS P) at 50
N 145
W, whereas the western gyre is less well known. The
Alaskan gyre forms an elongated (SW-NE) cyclonic dome in the halocline, shoaling to
75 m at the center. The dome, which is axial to circulation, can be identified by a surface
salinity maximum in the range 32.8–33.0%. Seasonal changes in the depth of the surface
layer of low-salinity water are slight, and it is effectively isolated from deep water by
the permanent halocline at 100–150 m. Changes in SST lag heat input at the surface by