Chapter 6
THE DEEP PACIFIC OCEAN FLOOR
Craig R. SMITH and Amanda W.J. DEMOPOULOS
INTRODUCTION
The Pacific is a vast ocean, stretching 15 000 kilometers
latitudinally from the Philippines to Panama, and
10 000 km longitudinally from the Southern Ocean to
Alaska (Fig. 6.1). It is, by roughly a factor of two,
the largest of all oceans, covering nearly a third of
the Earth’s surface. Because of its size, economic
importance, and proximity to major oceanographic
research centers, scientists have explored the deep
Pacific since the Challenger Expedition of the 1870s.
Portions of the deep Pacific seafloor (for example, the
slope of California, USA) are thus well studied by
deep-sea standards; nonetheless, many other regions of
the deep Pacific are no better known than the surface
of the moon.
In this chapter, we first review the general physical
characteristics of the deep Pacific Ocean. We then
discuss the distribution of key habitat variables, such as
substratum type, bottom-water oxygen, and particulate
organic-carbon flux, which affect the nature and
abundance of life at the ocean floor. We describe the
structure and function of a variety of representative
habitat types (excluding hydrothermal vents and cold
seeps, which are discussed Chapter 4), and speculate on
their distribution in the deep Pacific. Finally, we offer
some conclusions concerning the processes controlling
ecosystem structure and function in the deep Pacific
Ocean and identify research needs for the future.
PHYSICAL CHARACTERISTICS OF THE DEEP
PACIFIC OCEAN
The Pacific Ocean, excluding its adjacent seas (e.g.,
the Coral, China and Bering Seas: see Chapter 8)
covers roughly 166×10
6 km
2 , encompassing 46% of
the world ocean. Its average depth is 4190 m, exceeding
the average ocean depth by about 12%.
The morphology of the Pacific Ocean differs from
that of the other major oceans (the Atlantic and the
Indian) in three important ways. (1) The Pacific is
largely surrounded by deep ocean trenches abutting
on linear mountain chains (e.g., the Andes of South
America) or island arcs (e.g., the Aleutians and the
Marianas) (Fig. 6.1). The trenches, which range in
depth from 6700 to 11 000 m, form the deepest parts
of the ocean, and 11 of the worlds’ total of 14 trenches
occur in the Pacific. Ocean trenches and the marginal
seas behind island arcs act as sediment traps, largely
isolating the deep basins of the Pacific from the influx
of terrigenous (i.e., continental) sediments. Another
factor contributing to limited terrigenous sedimentation
in the Pacific is a low rate of river discharge; the
largest discharges of riverine sediments (e.g., from
the Ganges, Yellow, Indus and Amazon) are into the
Atlantic and Indian Oceans, or into marginal seas
(Berner, 1982; Kennett, 1982). As a consequence,
the Pacific lacks the large deposits of terrigenous
sediments that form smooth continental rises and
abyssal plains in the Atlantic and Indian Oceans. The
margins of the Pacific Ocean are instead typified by
narrow continental shelves and steep slopes, frequently
dissected by submarine canyons. In place of abyssal
plains covered by thick sediments, the basin floor in
most of the Pacific (85%) consists of abyssal hills with
heights of less than 1000 m and widths of 1 to 10 km,
blanketed by less than 100 m of sediment (Kennett,
1982).
Other distinctive morphological features of the
Pacific include (2) vast, continuous expanses of abyssal
seafloor and (3) an abundance of islands and seamounts
(Fig. 6.1). Unlike the Atlantic and Indian Oceans,
which are subdivided into a number of basins by long
179
THE DEEP PACIFIC OCEAN FLOOR
Craig R. SMITH and Amanda W.J. DEMOPOULOS
INTRODUCTION
The Pacific is a vast ocean, stretching 15 000 kilometers
latitudinally from the Philippines to Panama, and
10 000 km longitudinally from the Southern Ocean to
Alaska (Fig. 6.1). It is, by roughly a factor of two,
the largest of all oceans, covering nearly a third of
the Earth’s surface. Because of its size, economic
importance, and proximity to major oceanographic
research centers, scientists have explored the deep
Pacific since the Challenger Expedition of the 1870s.
Portions of the deep Pacific seafloor (for example, the
slope of California, USA) are thus well studied by
deep-sea standards; nonetheless, many other regions of
the deep Pacific are no better known than the surface
of the moon.
In this chapter, we first review the general physical
characteristics of the deep Pacific Ocean. We then
discuss the distribution of key habitat variables, such as
substratum type, bottom-water oxygen, and particulate
organic-carbon flux, which affect the nature and
abundance of life at the ocean floor. We describe the
structure and function of a variety of representative
habitat types (excluding hydrothermal vents and cold
seeps, which are discussed Chapter 4), and speculate on
their distribution in the deep Pacific. Finally, we offer
some conclusions concerning the processes controlling
ecosystem structure and function in the deep Pacific
Ocean and identify research needs for the future.
PHYSICAL CHARACTERISTICS OF THE DEEP
PACIFIC OCEAN
The Pacific Ocean, excluding its adjacent seas (e.g.,
the Coral, China and Bering Seas: see Chapter 8)
covers roughly 166×10
6 km
2 , encompassing 46% of
the world ocean. Its average depth is 4190 m, exceeding
the average ocean depth by about 12%.
The morphology of the Pacific Ocean differs from
that of the other major oceans (the Atlantic and the
Indian) in three important ways. (1) The Pacific is
largely surrounded by deep ocean trenches abutting
on linear mountain chains (e.g., the Andes of South
America) or island arcs (e.g., the Aleutians and the
Marianas) (Fig. 6.1). The trenches, which range in
depth from 6700 to 11 000 m, form the deepest parts
of the ocean, and 11 of the worlds’ total of 14 trenches
occur in the Pacific. Ocean trenches and the marginal
seas behind island arcs act as sediment traps, largely
isolating the deep basins of the Pacific from the influx
of terrigenous (i.e., continental) sediments. Another
factor contributing to limited terrigenous sedimentation
in the Pacific is a low rate of river discharge; the
largest discharges of riverine sediments (e.g., from
the Ganges, Yellow, Indus and Amazon) are into the
Atlantic and Indian Oceans, or into marginal seas
(Berner, 1982; Kennett, 1982). As a consequence,
the Pacific lacks the large deposits of terrigenous
sediments that form smooth continental rises and
abyssal plains in the Atlantic and Indian Oceans. The
margins of the Pacific Ocean are instead typified by
narrow continental shelves and steep slopes, frequently
dissected by submarine canyons. In place of abyssal
plains covered by thick sediments, the basin floor in
most of the Pacific (85%) consists of abyssal hills with
heights of less than 1000 m and widths of 1 to 10 km,
blanketed by less than 100 m of sediment (Kennett,
1982).
Other distinctive morphological features of the
Pacific include (2) vast, continuous expanses of abyssal
seafloor and (3) an abundance of islands and seamounts
(Fig. 6.1). Unlike the Atlantic and Indian Oceans,
which are subdivided into a number of basins by long
179