Atlantic Polar Biome
145
evolve. In March, the entire province exhibits low surface chlorophyll values, and it is only
during April, and only in the northeast quadrant of the Labrador Sea over deep water,
that a bloom is initiated. This pattern is concordant with the progression of regional
stratification, as we should expect it to be, although in the Labrador Sea there appear to
be regional consequences of buoyancy induced by ice-melt water. The Levitus data show
that it is in the northeast quadrant of the Labrador Sea that near-surface stratification
first develops. Furthermore, in April, mixed-layer depths shoaler than 40–50 m appear
here, while the remainder of the province remains deeply mixed.
Subsequently, in May, bloom conditions are much more extensive. The NE Labrador
Sea deep-water bloom is now continuous with chlorophyll accumulation along the West
Greenland Current, around Cape Farewell, and north along the coast to the GreenlandIceland Ridge. Again, this matches the evolution of regions having shallow mixed depths.
Similar conditions now also occur in the northern part of the Norwegian Basin, where
the mixed layer may exceed 30 m. So it is especially around the northern limbs of the two
subpolar cyclonic gyres, poleward of the trough of very deep winter mixed layers, that
chlorophyll accumulation is initiated. Also in May, the northward flow of the Irminger
Current around the western gyre supports a bloom.
In June, almost the entire province has shallow mixed-layer depths and while the
Labrador Sea bloom regresses into the southern limb of that gyre, the bloom in the
Greenland Sea occupies the entire eastern gyre. The Irminger Current east of Iceland
and its eastward extension within the Iceland Gap Front are now both prominent in
the chlorophyll field. From July onward, the regional features in the chlorophyll field
become more diffuse, and the chlorophyll concentration progressively diminishes. Finally,
in October, the Iceland Gap Front is the most prominent feature, though higher latitudes
are progressively less available to satellite imagery. Thus, later in the season, chlorophyll
accumulates preferentially in relation to active eddying along oceanic fronts, rather than
in relation to the start of regional stratification.
The spring bloom is dominated by diatoms (Chaetoceros, Nitzschia, chains of Melosira,
and pennate forms such as Navicula and Pleurosigma) and abundant athecate dinoflagellates. The colonial prymnesiophyte Phaeocystis pouchetti may be the dominant organism
in very early spring blooms, which are supported by extremely high rates of primary
production of <2 g C m
−2 d
−1 , or about the same rate as occurs in blooms at polar ice
edges (Smith et al., 1991a). The Phaeocystis blooms that occur in the Norwegian basin
in early May are contemporaneous with the spring bloom in the North Atlantic Drift
Province (NADR), initiated by thermal stratification approximately 30
farther south.
Recent investigations in the Labrador Sea (Lutz et al., 2003) confirm that the pico fraction
of autotrophic cells is relatively less important here than in adjacent lower latitudes; this
is now becoming a routine observation as is, perhaps, the universality of the haptophyte
fraction at both low and high latitudes.
The basic distribution and ecology of macrozooplankton of this province was established during the 1960s during Russian fishery investigations, although it should be noted
that they used the term “Davis Strait” for what we now call the entire Labrador Sea;
properly, of course, Davis Strait is the passage between Baffin Bay and the Labrador Sea. It
is also appropriate to recall the early time-series work at OWS “B” in the central Labrador
Sea, where daily BTs and weekly net tows and bottle casts were obtained throughout 1950
and into 1951 (Kielhorn, 1952). Ongoing Canadian investigations since 1994, along the
WOCE transects in the Labrador Sea, have emphasized the ecology and physiology of
the dominant taxa (e.g., Head et al., 2000). The partition of the accumulated CPR data
by Beaugrand et al. (2002a, b), already discussed in Chapter 7, offers further insights for
this region.
Herbivore ecology has the same characteristics as in BPLR, and the same organisms
are dominant. The ARCT province is clearly distinguished from more southerly provinces
145
evolve. In March, the entire province exhibits low surface chlorophyll values, and it is only
during April, and only in the northeast quadrant of the Labrador Sea over deep water,
that a bloom is initiated. This pattern is concordant with the progression of regional
stratification, as we should expect it to be, although in the Labrador Sea there appear to
be regional consequences of buoyancy induced by ice-melt water. The Levitus data show
that it is in the northeast quadrant of the Labrador Sea that near-surface stratification
first develops. Furthermore, in April, mixed-layer depths shoaler than 40–50 m appear
here, while the remainder of the province remains deeply mixed.
Subsequently, in May, bloom conditions are much more extensive. The NE Labrador
Sea deep-water bloom is now continuous with chlorophyll accumulation along the West
Greenland Current, around Cape Farewell, and north along the coast to the GreenlandIceland Ridge. Again, this matches the evolution of regions having shallow mixed depths.
Similar conditions now also occur in the northern part of the Norwegian Basin, where
the mixed layer may exceed 30 m. So it is especially around the northern limbs of the two
subpolar cyclonic gyres, poleward of the trough of very deep winter mixed layers, that
chlorophyll accumulation is initiated. Also in May, the northward flow of the Irminger
Current around the western gyre supports a bloom.
In June, almost the entire province has shallow mixed-layer depths and while the
Labrador Sea bloom regresses into the southern limb of that gyre, the bloom in the
Greenland Sea occupies the entire eastern gyre. The Irminger Current east of Iceland
and its eastward extension within the Iceland Gap Front are now both prominent in
the chlorophyll field. From July onward, the regional features in the chlorophyll field
become more diffuse, and the chlorophyll concentration progressively diminishes. Finally,
in October, the Iceland Gap Front is the most prominent feature, though higher latitudes
are progressively less available to satellite imagery. Thus, later in the season, chlorophyll
accumulates preferentially in relation to active eddying along oceanic fronts, rather than
in relation to the start of regional stratification.
The spring bloom is dominated by diatoms (Chaetoceros, Nitzschia, chains of Melosira,
and pennate forms such as Navicula and Pleurosigma) and abundant athecate dinoflagellates. The colonial prymnesiophyte Phaeocystis pouchetti may be the dominant organism
in very early spring blooms, which are supported by extremely high rates of primary
production of <2 g C m
−2 d
−1 , or about the same rate as occurs in blooms at polar ice
edges (Smith et al., 1991a). The Phaeocystis blooms that occur in the Norwegian basin
in early May are contemporaneous with the spring bloom in the North Atlantic Drift
Province (NADR), initiated by thermal stratification approximately 30
farther south.
Recent investigations in the Labrador Sea (Lutz et al., 2003) confirm that the pico fraction
of autotrophic cells is relatively less important here than in adjacent lower latitudes; this
is now becoming a routine observation as is, perhaps, the universality of the haptophyte
fraction at both low and high latitudes.
The basic distribution and ecology of macrozooplankton of this province was established during the 1960s during Russian fishery investigations, although it should be noted
that they used the term “Davis Strait” for what we now call the entire Labrador Sea;
properly, of course, Davis Strait is the passage between Baffin Bay and the Labrador Sea. It
is also appropriate to recall the early time-series work at OWS “B” in the central Labrador
Sea, where daily BTs and weekly net tows and bottle casts were obtained throughout 1950
and into 1951 (Kielhorn, 1952). Ongoing Canadian investigations since 1994, along the
WOCE transects in the Labrador Sea, have emphasized the ecology and physiology of
the dominant taxa (e.g., Head et al., 2000). The partition of the accumulated CPR data
by Beaugrand et al. (2002a, b), already discussed in Chapter 7, offers further insights for
this region.
Herbivore ecology has the same characteristics as in BPLR, and the same organisms
are dominant. The ARCT province is clearly distinguished from more southerly provinces