Chapter 5
THE DEEP ATLANTIC OCEAN
Lisa A. LEVIN and Andrew J. GOODAY
INTRODUCTION
The Atlantic Ocean is a long sinuous ocean which
originated during the Mesozoic following the breakup of the supercontinent of Pangea. For most of its
length, the eastern and western boundaries are clearly
defined by land masses, except where it is separated
from the Caribbean Sea and Gulf of Mexico by troughs
and trenches. The northern and southern limits are
more difficult to define. To the north we consider
the Atlantic to include the subpolar Greenland and
Norwegian Basins. These are linked hydrographically
to the rest of the Atlantic, although they are isolated
topographically by the ridge system extending between
Greenland and Scotland. To the south, the boundary
between the South Atlantic and Southern Ocean is
generally defined hydrologically by the Subtropical
Convergence around 40ºS (e.g., Webb, 1996).
In this chapter we review current knowledge about
the distribution and ecology of organisms on the floor
of the Atlantic Ocean from the continental slope to
the abyss, and describe the environmental setting that
they experience. We focus particularly on the North
Atlantic, since the literature for this hemisphere is
far more voluminous than for the South Atlantic.
As with any large review, we have been selective in
our coverage of the regional literature, concentrating
on aspects with which we are most familiar, or
which have received greatest attention from investigators. Our treatment of the Atlantic intentionally
omits hydrothermal vent and seep settings, which are
covered in Chapter 4 of this volume. Following a
description of the environment of the deep Atlantic,
and of the biological communities region by region,
we have attempted to synthesize general patterns of
faunal density and biomass, community respiration,
bioturbation and succession.
Distinctive features of the Atlantic Ocean
The two margins of the Atlantic separated between
about 175 and 90 million years ago, making it the
youngest of the major world oceans. Because of
its relative youth, the Atlantic is a narrow ocean,
with a relatively high ratio of margin to open water.
The configuration of the eastern and western sides
strongly influences the movement of surface currents
(Longhurst, 1998) and, ultimately, the nature of the
deep-sea biota. Because of the high ratio of margin
to open water in the Atlantic, mass wasting events
on the margins (involving the collapse and slumping
of sediments) affect a considerable fraction of the
deep ocean. Earthquake-induced turbidity flows may
sequester carbon originally deposited on the shallow
margins in deep-sea sediments (Thunell et al., 1999).
Regions such as the Madeira Abyssal Plain (Weaver
et al., 1992), the Grand Banks abyss (Huggett, 1987),
or the Cariaco Basin (Thunell et al., 1999) apparently
contain turbidite
1 sediments originating on the margin.
Despite the frequency of mass wasting along the
margin, the Atlantic is generally less tectonically active
than the Pacific. There are fewer subduction zones
and trenches, and thus less hadal habitat. Hydrocarbon
seeps, which are common along much of the active
Pacific margin, are apparently relatively rare in the
Atlantic, particularly on the eastern margins (Sibuet
and Olu, 1998). Sediment deposition is a dominant
process on the broad slope and rise. Strong bottom
1 Turbidite sediments are produced by deposition from gravity-driven flows of sediment ‘rivers’. They may be homogeneous, or characterized
by fining upward. See Glossary, p. 477.
111
THE DEEP ATLANTIC OCEAN
Lisa A. LEVIN and Andrew J. GOODAY
INTRODUCTION
The Atlantic Ocean is a long sinuous ocean which
originated during the Mesozoic following the breakup of the supercontinent of Pangea. For most of its
length, the eastern and western boundaries are clearly
defined by land masses, except where it is separated
from the Caribbean Sea and Gulf of Mexico by troughs
and trenches. The northern and southern limits are
more difficult to define. To the north we consider
the Atlantic to include the subpolar Greenland and
Norwegian Basins. These are linked hydrographically
to the rest of the Atlantic, although they are isolated
topographically by the ridge system extending between
Greenland and Scotland. To the south, the boundary
between the South Atlantic and Southern Ocean is
generally defined hydrologically by the Subtropical
Convergence around 40ºS (e.g., Webb, 1996).
In this chapter we review current knowledge about
the distribution and ecology of organisms on the floor
of the Atlantic Ocean from the continental slope to
the abyss, and describe the environmental setting that
they experience. We focus particularly on the North
Atlantic, since the literature for this hemisphere is
far more voluminous than for the South Atlantic.
As with any large review, we have been selective in
our coverage of the regional literature, concentrating
on aspects with which we are most familiar, or
which have received greatest attention from investigators. Our treatment of the Atlantic intentionally
omits hydrothermal vent and seep settings, which are
covered in Chapter 4 of this volume. Following a
description of the environment of the deep Atlantic,
and of the biological communities region by region,
we have attempted to synthesize general patterns of
faunal density and biomass, community respiration,
bioturbation and succession.
Distinctive features of the Atlantic Ocean
The two margins of the Atlantic separated between
about 175 and 90 million years ago, making it the
youngest of the major world oceans. Because of
its relative youth, the Atlantic is a narrow ocean,
with a relatively high ratio of margin to open water.
The configuration of the eastern and western sides
strongly influences the movement of surface currents
(Longhurst, 1998) and, ultimately, the nature of the
deep-sea biota. Because of the high ratio of margin
to open water in the Atlantic, mass wasting events
on the margins (involving the collapse and slumping
of sediments) affect a considerable fraction of the
deep ocean. Earthquake-induced turbidity flows may
sequester carbon originally deposited on the shallow
margins in deep-sea sediments (Thunell et al., 1999).
Regions such as the Madeira Abyssal Plain (Weaver
et al., 1992), the Grand Banks abyss (Huggett, 1987),
or the Cariaco Basin (Thunell et al., 1999) apparently
contain turbidite
1 sediments originating on the margin.
Despite the frequency of mass wasting along the
margin, the Atlantic is generally less tectonically active
than the Pacific. There are fewer subduction zones
and trenches, and thus less hadal habitat. Hydrocarbon
seeps, which are common along much of the active
Pacific margin, are apparently relatively rare in the
Atlantic, particularly on the eastern margins (Sibuet
and Olu, 1998). Sediment deposition is a dominant
process on the broad slope and rise. Strong bottom
1 Turbidite sediments are produced by deposition from gravity-driven flows of sediment ‘rivers’. They may be homogeneous, or characterized
by fining upward. See Glossary, p. 477.
111