112
Lisa A. LEVIN and Andrew J. GOODAY
flows, sometimes reaching storm proportions, are more
prevalent in the Atlantic than in other oceans. These
play an important role in redistributing sediments and
organic matter in deep water, leading to the formation
of vast sediment drifts (Hollister et al., 1984).
Atlantic water masses exhibit distinctive properties.
There is a strong flow of cold abyssal water from
both polar regions, whereas very little deep arctic
water directly enters the Pacific Ocean. The North
Atlantic is the source of much of the World Ocean’s
deep water. These young, near-bottom water masses
are better oxygenated, and the calcium compensation
depth
2 is much deeper, than in the Pacific and Indian
Oceans. This affects the distribution of sediment types.
Carbonate oozes are the dominant sediments in the
Atlantic, and carbonate-free red clays, which cover vast
tracts of the deep Pacific, are confined to relatively
small areas. Sedimentation rates are higher in the
central parts of the Atlantic, and manganese nodule
fields are less extensive than in the other oceans.
Massive upwelling, characteristic of eastern boundaries
in the Pacific and Indian Oceans, is less extensive in the
Atlantic, and the intense oxygen-minimum zones that
develop in these other oceans are limited to a small area
off West Africa.
The processes in the upper water column that drive
the timing and magnitude of primary production in
the Atlantic are different from those operating in the
Pacific (Longhurst, 1995, 1998). The spring bloom is
more intense and widespread in the North Atlantic than
anywhere else in the oceans, leading to a greater degree
of seasonality in surface production and to relatively
predictable seasonal inputs of phytodetritus to the deep
seabed. Particularly in marginal environments, much
of the marine primary production is deposited on the
seafloor, making the Atlantic margins highly dynamic
settings, with important roles in organic-matter cycling.
There is evidence that these inputs are more likely to
meet the respiratory demands of the benthos than in the
Pacific Ocean.
The youth of the Atlantic may also influence zoogeographic patterns. About a third of the benthic species
present in deep water appear to be endemic, and the degree of endemism increases with depth (Vinogradova,
1997). Some major groups are apparently absent or
poorly represented in the Atlantic. Different families
dominate the demersal fish fauna in the Atlantic
(in ranked order, the Macrouridae, Alepocephalidae,
Ophidiidae, Gadidae and Ragidae), and the NE Pacific (in ranked order, the Scorpaenidae, Liparidae,
Zoarcidae, Ragidae, Pleuronectidae and Macrouridae)
(Merrett and Haedrich, 1997). Among the protists, the
xenophyophore order Stannomida, which is common
and diverse in the Pacific, is represented in the
Atlantic by a single species. Atlantic vent faunas have
distinctive features as well. Vestimentiferans, common
in the Pacific, are absent from the Atlantic, whereas
bresiliid shrimps are a dominant element in the Atlantic
but not the Pacific (Gebruk et al., 1997). Because
many researchers and nations have concentrated their
efforts in one ocean or another, there are relatively
few investigations that compare deep-sea processes in
a global context. Future efforts to compare and contrast
the Atlantic with other world oceans and seas will
undoubtedly reveal additional unique features, as well
as unexpected commonalities.
HISTORY OF RESEARCH
The North Atlantic was a cradle for the development
of deep-sea biology both during the latter part of the
19th century and in recent decades. To some extent, this
reflects proximity to population centers and academic
institutions in western Europe and North America.
By the 1860s, a considerable number of observations, many of them made serendipitously during
sounding operations in the North Atlantic, strongly
suggested that animals could live on the ocean floor
(Rice, 1975; Rice et al., 1976; Mills, 1983). However,
the first concerted attempts to sample deep-sea animals
by means of dredges were made in the late 1860s in
the waters to the north and west of the British Isles,
initially from H.M.S. Lightning (1868) but principally
from H.M.S. Porcupine (1869, 1870). The deepest
sample taken during these early cruises demonstrated
that animal life could flourish at a depth of 4289 m.
It was these dredging activities which finally and
belatedly disproved the azoic theory of Forbes (1844).
They also paved the way for the great world-wide
Challenger Expedition of 1872–1876, which in turn
stimulated other European deep-sea campaigns such as
the French Travailleur and Talisman expeditions in the
Northeast Atlantic and Mediterranean, and the work of
Albert I of Monaco who introduced many innovative
methods into deep-sea biology (Mills, 1983). The
2 The calcium carbonate (calcite) compensation depth (CCD) is the depth at which <20% of skeletal carbonate is preserved in the sediment.
Lisa A. LEVIN and Andrew J. GOODAY
flows, sometimes reaching storm proportions, are more
prevalent in the Atlantic than in other oceans. These
play an important role in redistributing sediments and
organic matter in deep water, leading to the formation
of vast sediment drifts (Hollister et al., 1984).
Atlantic water masses exhibit distinctive properties.
There is a strong flow of cold abyssal water from
both polar regions, whereas very little deep arctic
water directly enters the Pacific Ocean. The North
Atlantic is the source of much of the World Ocean’s
deep water. These young, near-bottom water masses
are better oxygenated, and the calcium compensation
depth
2 is much deeper, than in the Pacific and Indian
Oceans. This affects the distribution of sediment types.
Carbonate oozes are the dominant sediments in the
Atlantic, and carbonate-free red clays, which cover vast
tracts of the deep Pacific, are confined to relatively
small areas. Sedimentation rates are higher in the
central parts of the Atlantic, and manganese nodule
fields are less extensive than in the other oceans.
Massive upwelling, characteristic of eastern boundaries
in the Pacific and Indian Oceans, is less extensive in the
Atlantic, and the intense oxygen-minimum zones that
develop in these other oceans are limited to a small area
off West Africa.
The processes in the upper water column that drive
the timing and magnitude of primary production in
the Atlantic are different from those operating in the
Pacific (Longhurst, 1995, 1998). The spring bloom is
more intense and widespread in the North Atlantic than
anywhere else in the oceans, leading to a greater degree
of seasonality in surface production and to relatively
predictable seasonal inputs of phytodetritus to the deep
seabed. Particularly in marginal environments, much
of the marine primary production is deposited on the
seafloor, making the Atlantic margins highly dynamic
settings, with important roles in organic-matter cycling.
There is evidence that these inputs are more likely to
meet the respiratory demands of the benthos than in the
Pacific Ocean.
The youth of the Atlantic may also influence zoogeographic patterns. About a third of the benthic species
present in deep water appear to be endemic, and the degree of endemism increases with depth (Vinogradova,
1997). Some major groups are apparently absent or
poorly represented in the Atlantic. Different families
dominate the demersal fish fauna in the Atlantic
(in ranked order, the Macrouridae, Alepocephalidae,
Ophidiidae, Gadidae and Ragidae), and the NE Pacific (in ranked order, the Scorpaenidae, Liparidae,
Zoarcidae, Ragidae, Pleuronectidae and Macrouridae)
(Merrett and Haedrich, 1997). Among the protists, the
xenophyophore order Stannomida, which is common
and diverse in the Pacific, is represented in the
Atlantic by a single species. Atlantic vent faunas have
distinctive features as well. Vestimentiferans, common
in the Pacific, are absent from the Atlantic, whereas
bresiliid shrimps are a dominant element in the Atlantic
but not the Pacific (Gebruk et al., 1997). Because
many researchers and nations have concentrated their
efforts in one ocean or another, there are relatively
few investigations that compare deep-sea processes in
a global context. Future efforts to compare and contrast
the Atlantic with other world oceans and seas will
undoubtedly reveal additional unique features, as well
as unexpected commonalities.
HISTORY OF RESEARCH
The North Atlantic was a cradle for the development
of deep-sea biology both during the latter part of the
19th century and in recent decades. To some extent, this
reflects proximity to population centers and academic
institutions in western Europe and North America.
By the 1860s, a considerable number of observations, many of them made serendipitously during
sounding operations in the North Atlantic, strongly
suggested that animals could live on the ocean floor
(Rice, 1975; Rice et al., 1976; Mills, 1983). However,
the first concerted attempts to sample deep-sea animals
by means of dredges were made in the late 1860s in
the waters to the north and west of the British Isles,
initially from H.M.S. Lightning (1868) but principally
from H.M.S. Porcupine (1869, 1870). The deepest
sample taken during these early cruises demonstrated
that animal life could flourish at a depth of 4289 m.
It was these dredging activities which finally and
belatedly disproved the azoic theory of Forbes (1844).
They also paved the way for the great world-wide
Challenger Expedition of 1872–1876, which in turn
stimulated other European deep-sea campaigns such as
the French Travailleur and Talisman expeditions in the
Northeast Atlantic and Mediterranean, and the work of
Albert I of Monaco who introduced many innovative
methods into deep-sea biology (Mills, 1983). The
2 The calcium carbonate (calcite) compensation depth (CCD) is the depth at which <20% of skeletal carbonate is preserved in the sediment.