132
Chapter 9: The Atlantic Ocean
organic material to the sea floor is faster than horizontal advection of nutrients into the
region of deep mixing. The result is a nutrient front at 1000 m across the ocean at about
30
N for nitrate, phosphate, and silicate that has no counterpart in other ocean basins.
In the North Atlantic, the bifurcation of the Gulf Stream over the Newfoundland
Basin adds complexity to the gyral system, which is reflected in its dynamic biogeography,
and requires that we recognize compartments within the gyral circulation, though they
may not be readily identifiable in surface features. At about 40–45
W the Gulf Stream
feeds a southeasterly flow (the Azores Current) directly into the gyral circulation and a
northeasterly flow (the North Atlantic Current), of which part recirculates into the gyre
only when it encounters the European continent. Midocean ridge topography restricts the
main gyral recirculation to the western basin, so there are significant biological differences
between the eastern and western parts of the gyre. The passage of Gulf Stream water
across the ridge is often marked by a southerly loop associated with the topography.
Atlantic Polar Biome
The coastal geography of the polar region of the Atlantic is rather complex, especially
in the Canadian archipelago, and the marginal ice zone (MIZ) that migrates through
these regions during the summer has many of the characteristics of a coastal zone. It is
therefore not useful to recognize a coastal boundary zone poleward of the North Atlantic
continental shelf provinces.
Boreal Polar Province (BPLR)
Extent of the Province
It is ironic that for BPLR, the first province to be discussed in detail, it is better not to follow
the logic of the four biomes discussed in Chapter 6. This is because the complexity of the
arctic archipelago of northern Canada and the difficulty of access of the northern Asiatic
coastline make it very difficult to sustain an adequate description of the coastal biome
here. This province, therefore, comprises the Arctic Ocean, lying between North America,
Greenland, and Asia, together with all but one of its marginal seas: the Chukchi, East Siberian,
Laptev, Kara, and Beaufort Seas. Only the northern part of Barents Sea is included in BPLR;
the southern part is assigned to SARC, because it is strongly influenced by Atlantic Current
water and does not freeze over in winter. The boundary between BPLR and SARC in the
Barents Sea is the well-marked thermal front between Atlantic and Arctic water that passes
around Bear Island and meanders eastward from Hope Island at about 74–78
N. Hudson
Bay is included in BPLR, as is the entire coastline of the Arctic basin except that of the
Barents Sea. The coasts of both eastern and western Greenland, and of Labrador south to
Hamilton Bank, are included: all of these have extreme polar conditions.
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
The Arctic Ocean (3 × 10
6 km
2 ) has wide continental shelves reaching 700–800 km along
much of the north coast of Russia: the Eastern Siberian, Lapta, and Kara Seas have extensive shelf regions although these seas, as defined by geographers, include both shelf and
adjacent deep water. Tidal streams are very strong in some embayments of the Laptev shelf.
Off northern Alaska the shelf narrows to only < 250 km and is even narrower to the
east, across the Beaufort Sea toward the Mackenzie delta. The shelves of the north coasts
of the Canadian archipelago and Greenland are narrower still, though the archipelago
itself extends over 15
of latitude. The continental shelf off Labrador is remarkable for its
Chapter 9: The Atlantic Ocean
organic material to the sea floor is faster than horizontal advection of nutrients into the
region of deep mixing. The result is a nutrient front at 1000 m across the ocean at about
30
N for nitrate, phosphate, and silicate that has no counterpart in other ocean basins.
In the North Atlantic, the bifurcation of the Gulf Stream over the Newfoundland
Basin adds complexity to the gyral system, which is reflected in its dynamic biogeography,
and requires that we recognize compartments within the gyral circulation, though they
may not be readily identifiable in surface features. At about 40–45
W the Gulf Stream
feeds a southeasterly flow (the Azores Current) directly into the gyral circulation and a
northeasterly flow (the North Atlantic Current), of which part recirculates into the gyre
only when it encounters the European continent. Midocean ridge topography restricts the
main gyral recirculation to the western basin, so there are significant biological differences
between the eastern and western parts of the gyre. The passage of Gulf Stream water
across the ridge is often marked by a southerly loop associated with the topography.
Atlantic Polar Biome
The coastal geography of the polar region of the Atlantic is rather complex, especially
in the Canadian archipelago, and the marginal ice zone (MIZ) that migrates through
these regions during the summer has many of the characteristics of a coastal zone. It is
therefore not useful to recognize a coastal boundary zone poleward of the North Atlantic
continental shelf provinces.
Boreal Polar Province (BPLR)
Extent of the Province
It is ironic that for BPLR, the first province to be discussed in detail, it is better not to follow
the logic of the four biomes discussed in Chapter 6. This is because the complexity of the
arctic archipelago of northern Canada and the difficulty of access of the northern Asiatic
coastline make it very difficult to sustain an adequate description of the coastal biome
here. This province, therefore, comprises the Arctic Ocean, lying between North America,
Greenland, and Asia, together with all but one of its marginal seas: the Chukchi, East Siberian,
Laptev, Kara, and Beaufort Seas. Only the northern part of Barents Sea is included in BPLR;
the southern part is assigned to SARC, because it is strongly influenced by Atlantic Current
water and does not freeze over in winter. The boundary between BPLR and SARC in the
Barents Sea is the well-marked thermal front between Atlantic and Arctic water that passes
around Bear Island and meanders eastward from Hope Island at about 74–78
N. Hudson
Bay is included in BPLR, as is the entire coastline of the Arctic basin except that of the
Barents Sea. The coasts of both eastern and western Greenland, and of Labrador south to
Hamilton Bank, are included: all of these have extreme polar conditions.
Continental Shelf Topography and Tidal and Shelf-Edge Fronts
The Arctic Ocean (3 × 10
6 km
2 ) has wide continental shelves reaching 700–800 km along
much of the north coast of Russia: the Eastern Siberian, Lapta, and Kara Seas have extensive shelf regions although these seas, as defined by geographers, include both shelf and
adjacent deep water. Tidal streams are very strong in some embayments of the Laptev shelf.
Off northern Alaska the shelf narrows to only < 250 km and is even narrower to the
east, across the Beaufort Sea toward the Mackenzie delta. The shelves of the north coasts
of the Canadian archipelago and Greenland are narrower still, though the archipelago
itself extends over 15
of latitude. The continental shelf off Labrador is remarkable for its