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Chapter 9: The Atlantic Ocean
depth of the mixed layer. This is an excellent illustration of the numerical dominance of
Prochlorococcus in low-biomass oligotrophic situations and of the general dominance of
biomass—because they are larger cells—of the picoeukaryotes.
The Russian biogeographic studies do not help us a great deal: an extremely detailed
listing of the distributions of 574 species of phytoplankton obtained from visual cell
counts and of mesozooplankton species counts from 1300 stations (including 416 species
of copepods) was reduced by Piontkowski et al. (2003) to spatial distributions of indices
of relative diversity, which is greatest, as we might expect, on the western, more dynamic
side of the gyre. It is noted that although many species of both groups occur everywhere in the gyre, others occur only in specific regions of flow. The calculated ratio of
group abundance is such that mesozooplankton carbon biomass may be expressed as an
exponential function of phytoplankton carbon.
Thus, the emphasis in studies of zooplankton in the South Atlantic has so far been
distributional in nature and most have been concerned specifically with the SW Atlantic.
Distribution envelopes derived from presence-absence data have frequently been plotted,
as by Boltovsky (1986) for many taxonomic groups, from which he inferred more than
20 different characteristic patterns of “biogeographic zonations, transition zones and
communities” between equatorial and polar latitudes in the western South Atlantic. He
compared these with the large-scale distribution of euphausiids in the Pacific according
to Brinton, and emphasized that in both cases, many species cross what he describes
as “boundaries between water masses.” By far the most critical and useful study that
I have seen is that of Gibbons (1997), who compared distribution of all euphausiids
species on a 5
grid, as already discussed in Chapter 1. This emphasizes that the major
changes in distribution occur across the subtropical convergence zone and that change is
weaker between the gyral populations and those within the equatorial zones to the north.
Gibbons emphasizes the differentiation of pelagic ecosystems by the characteristic relative
abundances of species that occur in both entities: such differences are not exposed in the
habitual presence/absence data of biogeographers.
Synopsis
Case 3—Winter-spring production with nutrient limitation—All seasonal changes, integrated over the province, have very weak amplitude but are reasonably consistent.
Z m undergoes a moderate austral winter excursion from 25 m in February–March to
60 m in May–September; because Z eu remains between 50 and 70 m, the thermocline is
almost constantly illuminated. P rate increases consistently from austral spring August–
September, reaching and briefly sustaining higher values in October–November; the
production rate then declines, prior to austral midsummer, and the decrease is linear to April–May, just before austral midwinter (Fig. 9.21). Chlorophyll accumulation
begins earlier and, in some years, maximum chlorophyll biomass occurs 60 days before
maximum P rate is achieved.
Atlantic Coastal Biome
Northeast Atlantic Shelves Province (NECS)
Extent of the Province
The Northeast Atlantic Shelves Province (NECS) comprises the continental shelf of
western Europe, from Cape Finisterre in NW Spain to the Skagerrak north of Denmark,
and thence into, and including, the Baltic Sea. The edge of the deep Faeroe-Shetland
Chapter 9: The Atlantic Ocean
depth of the mixed layer. This is an excellent illustration of the numerical dominance of
Prochlorococcus in low-biomass oligotrophic situations and of the general dominance of
biomass—because they are larger cells—of the picoeukaryotes.
The Russian biogeographic studies do not help us a great deal: an extremely detailed
listing of the distributions of 574 species of phytoplankton obtained from visual cell
counts and of mesozooplankton species counts from 1300 stations (including 416 species
of copepods) was reduced by Piontkowski et al. (2003) to spatial distributions of indices
of relative diversity, which is greatest, as we might expect, on the western, more dynamic
side of the gyre. It is noted that although many species of both groups occur everywhere in the gyre, others occur only in specific regions of flow. The calculated ratio of
group abundance is such that mesozooplankton carbon biomass may be expressed as an
exponential function of phytoplankton carbon.
Thus, the emphasis in studies of zooplankton in the South Atlantic has so far been
distributional in nature and most have been concerned specifically with the SW Atlantic.
Distribution envelopes derived from presence-absence data have frequently been plotted,
as by Boltovsky (1986) for many taxonomic groups, from which he inferred more than
20 different characteristic patterns of “biogeographic zonations, transition zones and
communities” between equatorial and polar latitudes in the western South Atlantic. He
compared these with the large-scale distribution of euphausiids in the Pacific according
to Brinton, and emphasized that in both cases, many species cross what he describes
as “boundaries between water masses.” By far the most critical and useful study that
I have seen is that of Gibbons (1997), who compared distribution of all euphausiids
species on a 5
grid, as already discussed in Chapter 1. This emphasizes that the major
changes in distribution occur across the subtropical convergence zone and that change is
weaker between the gyral populations and those within the equatorial zones to the north.
Gibbons emphasizes the differentiation of pelagic ecosystems by the characteristic relative
abundances of species that occur in both entities: such differences are not exposed in the
habitual presence/absence data of biogeographers.
Synopsis
Case 3—Winter-spring production with nutrient limitation—All seasonal changes, integrated over the province, have very weak amplitude but are reasonably consistent.
Z m undergoes a moderate austral winter excursion from 25 m in February–March to
60 m in May–September; because Z eu remains between 50 and 70 m, the thermocline is
almost constantly illuminated. P rate increases consistently from austral spring August–
September, reaching and briefly sustaining higher values in October–November; the
production rate then declines, prior to austral midsummer, and the decrease is linear to April–May, just before austral midwinter (Fig. 9.21). Chlorophyll accumulation
begins earlier and, in some years, maximum chlorophyll biomass occurs 60 days before
maximum P rate is achieved.
Atlantic Coastal Biome
Northeast Atlantic Shelves Province (NECS)
Extent of the Province
The Northeast Atlantic Shelves Province (NECS) comprises the continental shelf of
western Europe, from Cape Finisterre in NW Spain to the Skagerrak north of Denmark,
and thence into, and including, the Baltic Sea. The edge of the deep Faeroe-Shetland