THE DEEP ATLANTIC OCEAN
115
Table 5.1, continued
Project
Dates
Study area
Purpose
Atlantic Continental
Slope and Rise Study
(ASCAR) North Atlantic
Bight, Mid Atlantic
Bight, South Atlantic
Bight
1983–1986
NW Atlantic slope and
rise: 28ºN to 42ºN
US Minerals
Management Service,
sediment and faunal
surveys, canyon study
Shelf Edge Exchange
Processes (SEEP I)
1983–1984
U.S. Mid Atlantic Bight,
south of Long Island and
New Jersey
Carbon export and
transformation within
shelf and slope sediments
Shelf Edge Exchange
Processes (SEEP II)
1988–1989
U.S., Southern Mid
Atlantic Bight
Carbon export and
transformation within
shelf and slope sediments
High Energy Benthic
Boundary Layer
Experiment (HEBBLE)
1980–1986
Nova Scotia Rise
Physical, geological, and
faunal studies of
environment subject to
benthic storms
wide continental shelves developed off Newfoundland,
southern South America and northwestern Europe, and
the continental rises and abyssal aprons which are
particularly expansive in the South Atlantic and the
northern part of the North Atlantic (Emery and Uchupi,
1984: figs. 10–12 therein). Extensive carbonate platforms are developed in the western Atlantic, notably
the Blake Plateau and Bermuda Rise. Unlike those in
the Pacific, the continental margins on both sides of the
Atlantic are largely passive. However, active margins
with deep trenches (maximum depths 8414 m and
8264 m, respectively) are present in the western Atlantic (Puerto Rico Trench) and southern Atlantic
(South Sandwich Trench). Smaller-scale (third-order)
physiographic features include submarine canyons,
which are particularly numerous on the continental
margin off the northeastern United States, western
Europe and parts of northwestern Africa (Emery and
Uchupi, 1984: fig. 37 therein). Some extend into deepsea channels, probably created by turbidity currents
originating from the canyons. These features meander
across the continental rises and abyssal plains. Canyons
may have an important effect on the composition of
associated biological communities.
Deep-water hydrography
The large-scale hydrography of the Atlantic Ocean is
dominated by the overall northward movement of warm
surface and intermediate water, derived ultimately
from the Pacific and Indian Oceans, through the
South Atlantic and into the North Atlantic, where it
becomes more saline through evaporation (Broecker,
1991; Schmitz, 1995). On reaching the Greenland–
Norwegian Sea, this water is subject to intense winter
cooling and sinks by vertical convection. The resulting
Norwegian Sea deep water spills over the Faroe Bank
Channel and the Faroe–Iceland Ridge and entrains
resident Atlantic water to form Northeast Atlantic
Deep Water (NEADW). This water mass finds its way
into the Northwest Atlantic basin where it mixes with
bottom water flowing through the Denmark Strait and
low–salinity water from the Labrador Sea to form a
composite water mass termed North Atlantic Deep
Water (NADW). North Atlantic Deep Water flows
southwards into the South Atlantic and eventually back
into the Indian and Pacific Oceans via the Circumpolar
Current (Worthington, 1976; Gage and Tyler, 1991).
This ‘thermohaline conveyer belt’ (Broecker, 1991;
Rahmsdorf, 1997) leads to a net transfer of heat from
the south to the north (‘North Atlantic heat piracy’:
Berger and Wefer, 1996).
Other water masses are also present in the North Atlantic. The deep (>4500 m) basins off Northwest Africa
are occupied by Antarctic Bottom Water (AABW),
which enters the North Atlantic via the Vema Gap.
At depths greater than 2000 m, the dominant Northeast
Atlantic water mass is Mediterranean Water, which
flows through the Straits of Gibraltar, around the
Northwest European continental margin, and through
115
Table 5.1, continued
Project
Dates
Study area
Purpose
Atlantic Continental
Slope and Rise Study
(ASCAR) North Atlantic
Bight, Mid Atlantic
Bight, South Atlantic
Bight
1983–1986
NW Atlantic slope and
rise: 28ºN to 42ºN
US Minerals
Management Service,
sediment and faunal
surveys, canyon study
Shelf Edge Exchange
Processes (SEEP I)
1983–1984
U.S. Mid Atlantic Bight,
south of Long Island and
New Jersey
Carbon export and
transformation within
shelf and slope sediments
Shelf Edge Exchange
Processes (SEEP II)
1988–1989
U.S., Southern Mid
Atlantic Bight
Carbon export and
transformation within
shelf and slope sediments
High Energy Benthic
Boundary Layer
Experiment (HEBBLE)
1980–1986
Nova Scotia Rise
Physical, geological, and
faunal studies of
environment subject to
benthic storms
wide continental shelves developed off Newfoundland,
southern South America and northwestern Europe, and
the continental rises and abyssal aprons which are
particularly expansive in the South Atlantic and the
northern part of the North Atlantic (Emery and Uchupi,
1984: figs. 10–12 therein). Extensive carbonate platforms are developed in the western Atlantic, notably
the Blake Plateau and Bermuda Rise. Unlike those in
the Pacific, the continental margins on both sides of the
Atlantic are largely passive. However, active margins
with deep trenches (maximum depths 8414 m and
8264 m, respectively) are present in the western Atlantic (Puerto Rico Trench) and southern Atlantic
(South Sandwich Trench). Smaller-scale (third-order)
physiographic features include submarine canyons,
which are particularly numerous on the continental
margin off the northeastern United States, western
Europe and parts of northwestern Africa (Emery and
Uchupi, 1984: fig. 37 therein). Some extend into deepsea channels, probably created by turbidity currents
originating from the canyons. These features meander
across the continental rises and abyssal plains. Canyons
may have an important effect on the composition of
associated biological communities.
Deep-water hydrography
The large-scale hydrography of the Atlantic Ocean is
dominated by the overall northward movement of warm
surface and intermediate water, derived ultimately
from the Pacific and Indian Oceans, through the
South Atlantic and into the North Atlantic, where it
becomes more saline through evaporation (Broecker,
1991; Schmitz, 1995). On reaching the Greenland–
Norwegian Sea, this water is subject to intense winter
cooling and sinks by vertical convection. The resulting
Norwegian Sea deep water spills over the Faroe Bank
Channel and the Faroe–Iceland Ridge and entrains
resident Atlantic water to form Northeast Atlantic
Deep Water (NEADW). This water mass finds its way
into the Northwest Atlantic basin where it mixes with
bottom water flowing through the Denmark Strait and
low–salinity water from the Labrador Sea to form a
composite water mass termed North Atlantic Deep
Water (NADW). North Atlantic Deep Water flows
southwards into the South Atlantic and eventually back
into the Indian and Pacific Oceans via the Circumpolar
Current (Worthington, 1976; Gage and Tyler, 1991).
This ‘thermohaline conveyer belt’ (Broecker, 1991;
Rahmsdorf, 1997) leads to a net transfer of heat from
the south to the north (‘North Atlantic heat piracy’:
Berger and Wefer, 1996).
Other water masses are also present in the North Atlantic. The deep (>4500 m) basins off Northwest Africa
are occupied by Antarctic Bottom Water (AABW),
which enters the North Atlantic via the Vema Gap.
At depths greater than 2000 m, the dominant Northeast
Atlantic water mass is Mediterranean Water, which
flows through the Straits of Gibraltar, around the
Northwest European continental margin, and through