Atlantic Westerly Winds Biome
163
autumnal Z m deepening. Chlorophyll accumulates in the period March–May during the
P increase, and in September–October the rate of seasonal decrease is reduced, consistent
with a reduction in consumption as copepods migrate down out of the photic zone in
July–September.
Gulf Stream Province (GFST)
Extent of the Province
The Gulf Stream Province (GFST) includes the offshore Florida Current and the Gulf
Stream from Cape Hatteras to the Newfoundland Basin, where partition of flow occurs
into southeast and northeastward streams (see NADR). The landward margin of the
province is the North Wall of the Gulf Stream off the eastern United States and the
shelf-edge front farther to the south. The line between the field of cold-core eddies and
the warm water of the jet current defines the northern limit of the province after the
Gulf Stream has detached from the shelf. The southeastern boundary is more difficult to
define, but is best thought of as constrained by the distribution of energetic mesoscale
eddies.
Defining Characteristics of Regional Oceanography
Western boundary currents owe their relative strength to the zonal propagation of Rossby
waves, which accumulate energy on the western margin of oceans, and its subsequent
dissipation within the current. The Florida Current/Gulf Stream continuum is the western
boundary current of the North Atlantic and is prominent as a group of closely spaced
isotherms not only in hydrographic sections (e.g., Schroeder, 1965) but also in the surface
thermal field.
Originating in flow of North Equatorial Current water through the Florida Straits,
the velocity maximum of the Gulf Stream is topographically locked to the edge of the
continental shelf as far north as Cape Hatteras, where the coastline veers westward, and it
separates from the continental edge, to pass toward the northeast across deep water. The
region of separation is dynamic, and episodes of surfacing of nutrient-rich North Atlantic
central water occur in response to offshore meanders. After separation, the Gulf Stream
behaves as a free inertial jet until it encounters the Newfoundland Rise, around which
it continues (Fig. 9.7). A semipermanent loop passes around the Newfoundland Basin
before continuing eastward into the NAC: this loop, or “ring meander,” intermittently
pinches off a mesoscale eddy that carries warm-water organisms far to the north into the
Labrador Sea.
Although slope water forms a prominent, cold North Wall to landward of the stream,
it is important to note that a shelf-slope front (marked by the 34% isohaline) within
the slope water lies landward of the North Wall of the Gulf Stream so that confusion is
possible between the two features. This region has what must be the strongest horizontal
temperature gradient of SST anywhere in the oceans: in winter, 18
C Sargasso water and
the pack ice of the Gulf of St. Lawrence are only 300–400 km apart. No wonder, then, that
the GFST province is a region of rapid weather change and strong mesoscale variability.
Summer stratification occurs right across Slope water, Gulf Stream, and Sargasso Sea and
obscures the surface thermal gradient across the cold wall of the current.
The free inertial jet forms both cyclonic and anticyclonic meanders, and when these
turn acutely enough to become pinched off, isolated mesoscale features are formed. Each
is either a ring of isolated Gulf Stream water enclosing an area of cold slope water
163
autumnal Z m deepening. Chlorophyll accumulates in the period March–May during the
P increase, and in September–October the rate of seasonal decrease is reduced, consistent
with a reduction in consumption as copepods migrate down out of the photic zone in
July–September.
Gulf Stream Province (GFST)
Extent of the Province
The Gulf Stream Province (GFST) includes the offshore Florida Current and the Gulf
Stream from Cape Hatteras to the Newfoundland Basin, where partition of flow occurs
into southeast and northeastward streams (see NADR). The landward margin of the
province is the North Wall of the Gulf Stream off the eastern United States and the
shelf-edge front farther to the south. The line between the field of cold-core eddies and
the warm water of the jet current defines the northern limit of the province after the
Gulf Stream has detached from the shelf. The southeastern boundary is more difficult to
define, but is best thought of as constrained by the distribution of energetic mesoscale
eddies.
Defining Characteristics of Regional Oceanography
Western boundary currents owe their relative strength to the zonal propagation of Rossby
waves, which accumulate energy on the western margin of oceans, and its subsequent
dissipation within the current. The Florida Current/Gulf Stream continuum is the western
boundary current of the North Atlantic and is prominent as a group of closely spaced
isotherms not only in hydrographic sections (e.g., Schroeder, 1965) but also in the surface
thermal field.
Originating in flow of North Equatorial Current water through the Florida Straits,
the velocity maximum of the Gulf Stream is topographically locked to the edge of the
continental shelf as far north as Cape Hatteras, where the coastline veers westward, and it
separates from the continental edge, to pass toward the northeast across deep water. The
region of separation is dynamic, and episodes of surfacing of nutrient-rich North Atlantic
central water occur in response to offshore meanders. After separation, the Gulf Stream
behaves as a free inertial jet until it encounters the Newfoundland Rise, around which
it continues (Fig. 9.7). A semipermanent loop passes around the Newfoundland Basin
before continuing eastward into the NAC: this loop, or “ring meander,” intermittently
pinches off a mesoscale eddy that carries warm-water organisms far to the north into the
Labrador Sea.
Although slope water forms a prominent, cold North Wall to landward of the stream,
it is important to note that a shelf-slope front (marked by the 34% isohaline) within
the slope water lies landward of the North Wall of the Gulf Stream so that confusion is
possible between the two features. This region has what must be the strongest horizontal
temperature gradient of SST anywhere in the oceans: in winter, 18
C Sargasso water and
the pack ice of the Gulf of St. Lawrence are only 300–400 km apart. No wonder, then, that
the GFST province is a region of rapid weather change and strong mesoscale variability.
Summer stratification occurs right across Slope water, Gulf Stream, and Sargasso Sea and
obscures the surface thermal gradient across the cold wall of the current.
The free inertial jet forms both cyclonic and anticyclonic meanders, and when these
turn acutely enough to become pinched off, isolated mesoscale features are formed. Each
is either a ring of isolated Gulf Stream water enclosing an area of cold slope water