182
Craig R. SMITH and Amanda W.J. DEMOPOULOS
eastern boundaries of the North and South Pacific. Near
the equator, easterly trade winds impose a westward
stress on surface waters. Because of the Coriolis force,
this stress is converted to northward water transport
in the northern hemisphere and southward transport
in the southern hemisphere, producing a divergence of
surface waters and upwelling of deep waters laden with
nutrients (including iron) along the equator (Tomczak
and Godfrey, 1994; Landry et al., 1997). The upwelled
nutrients stimulate phytoplankton production, yielding
a band of high primary productivity within a few
degrees of the equator, extending from 90ºW to 160ºW
(Longhurst et al., 1995); the underlying abyss in turn
experiences an enhanced flux of particulate organic carbon from biogenic particles sinking from the productive
equatorial euphotic zone (Honjo et al., 1995; Smith
et al., 1997). In addition to upwelling, the equatorial
zone is often characterized by high current velocities
(up to 20 cm s
−1 ) to depths of at least 1500 m (Tomczak
and Godfrey, 1994).
Similar, but more intense, upwelling occurs along
the eastern boundary of the Pacific along the coast
of South America from 10 to 43ºS, and along the
coast of the American states of Washington, Oregon
and California in the northern hemisphere (Tomczak
and Godfrey, 1994). This eastern boundary upwelling
is caused by equatorward, longshore winds in the
coastal zone, which result in offshore transport of
surface waters because of Coriolis forces. Surface
water transported offshore is replaced by upwelling of
nutrient-laden deeper waters, yielding a band of very
high phytoplankton production within about 100 km of
the coast. The Peru–Chile upwelling system is the most
intense in the World Ocean and yields a massive flux
of sinking particulate organic carbon to the shelf and
slope of South America. Near the equator, the Peru–
Chile and equatorial upwelling systems merge to yield
high levels of primary production, and a deep flux
of particulate organic carbon, throughout the eastern
equatorial Pacific. The upwelling system off the west
coast of North America is seasonal (occurring from
April to September) and is less intense, but it still
causes a high flux of particulate organic carbon to the
continental slopes of the states of Washington, Oregon
and California. Shelf and slope waters beneath these
upwelling zones frequently are depleted of oxygen as
a result of high rates of degradation of particulate
organic carbon, and the underlying sediments typically
are organic-rich.
Water masses in contact with the floor of the deep
Pacific Ocean consist of three general types. Below
depths of 3000 m, the Pacific seafloor is bathed in
Antarctic Bottom Water – that is, very cold (0.5–1.5ºC),
relatively saline water formed predominantly in the
Weddell and Ross Seas during sea ice formation in
the Austral winter (Sverdrup et al., 1942; Tomczak
and Godfrey, 1994). This bottom water spills down the
slope of the Antarctic continent and circumnavigates
the globe in the Southern Ocean before moving
northward along the western margin of the Pacific
and slowly spreading eastward to cover the abyssal
Pacific seafloor. Between depths of 1000 and 3000 m,
the Pacific is filled with Pacific Deep Water formed
by slow mixing of Antarctic Bottom Water, North
Atlantic Deep Water advected from the North Atlantic
Ocean, and Intermediate Water from depths of less
than 1000 m (Tomczak and Godfrey, 1994). In the
North Pacific, much of the Deep Water may have last
contacted the atmosphere and taken up oxygen more
than 1000 years ago; as a consequence, this water
mass has relatively low levels of oxygen (although
typically not low enough to be biologically stressful).
Between depths of 500 m and 1000 m, the Pacific
is filled with Intermediate Water formed in either
the Antarctic or Arctic polar frontal regions, which
occur at roughly 60ºS and 40ºN, respectively. These
intermediate waters meet and upwell near the equator,
and are characterized by relatively low salinity and
temperatures that are warm (>3ºC) by deep-sea standards (Tomczak and Godfrey, 1994). In the northern
hemisphere, the intermediate waters are often formed
by subsurface mixing (i.e., they are not in atmospheric
contact during formation) and thus may be relatively
depleted in oxygen, contributing to formation of the
oxygen-minimum zone (see below, pp. 184–185).
KEY HABITAT VARIABLES AND THEIR REGIONAL
VARIATION IN THE PACIFIC
Several habitat variables play key roles in regulating
the nature and abundance of life on the deep-sea floor.
These include (1) substratum type (e.g., rocky versus
soft sediments), (2) near-bottom current velocities,
(3) bottom-water oxygen content, and (4) the vertical
flux of particulate organic carbon to the seafloor.
Substratum type
Substratum type controls, or at least is correlated
Craig R. SMITH and Amanda W.J. DEMOPOULOS
eastern boundaries of the North and South Pacific. Near
the equator, easterly trade winds impose a westward
stress on surface waters. Because of the Coriolis force,
this stress is converted to northward water transport
in the northern hemisphere and southward transport
in the southern hemisphere, producing a divergence of
surface waters and upwelling of deep waters laden with
nutrients (including iron) along the equator (Tomczak
and Godfrey, 1994; Landry et al., 1997). The upwelled
nutrients stimulate phytoplankton production, yielding
a band of high primary productivity within a few
degrees of the equator, extending from 90ºW to 160ºW
(Longhurst et al., 1995); the underlying abyss in turn
experiences an enhanced flux of particulate organic carbon from biogenic particles sinking from the productive
equatorial euphotic zone (Honjo et al., 1995; Smith
et al., 1997). In addition to upwelling, the equatorial
zone is often characterized by high current velocities
(up to 20 cm s
−1 ) to depths of at least 1500 m (Tomczak
and Godfrey, 1994).
Similar, but more intense, upwelling occurs along
the eastern boundary of the Pacific along the coast
of South America from 10 to 43ºS, and along the
coast of the American states of Washington, Oregon
and California in the northern hemisphere (Tomczak
and Godfrey, 1994). This eastern boundary upwelling
is caused by equatorward, longshore winds in the
coastal zone, which result in offshore transport of
surface waters because of Coriolis forces. Surface
water transported offshore is replaced by upwelling of
nutrient-laden deeper waters, yielding a band of very
high phytoplankton production within about 100 km of
the coast. The Peru–Chile upwelling system is the most
intense in the World Ocean and yields a massive flux
of sinking particulate organic carbon to the shelf and
slope of South America. Near the equator, the Peru–
Chile and equatorial upwelling systems merge to yield
high levels of primary production, and a deep flux
of particulate organic carbon, throughout the eastern
equatorial Pacific. The upwelling system off the west
coast of North America is seasonal (occurring from
April to September) and is less intense, but it still
causes a high flux of particulate organic carbon to the
continental slopes of the states of Washington, Oregon
and California. Shelf and slope waters beneath these
upwelling zones frequently are depleted of oxygen as
a result of high rates of degradation of particulate
organic carbon, and the underlying sediments typically
are organic-rich.
Water masses in contact with the floor of the deep
Pacific Ocean consist of three general types. Below
depths of 3000 m, the Pacific seafloor is bathed in
Antarctic Bottom Water – that is, very cold (0.5–1.5ºC),
relatively saline water formed predominantly in the
Weddell and Ross Seas during sea ice formation in
the Austral winter (Sverdrup et al., 1942; Tomczak
and Godfrey, 1994). This bottom water spills down the
slope of the Antarctic continent and circumnavigates
the globe in the Southern Ocean before moving
northward along the western margin of the Pacific
and slowly spreading eastward to cover the abyssal
Pacific seafloor. Between depths of 1000 and 3000 m,
the Pacific is filled with Pacific Deep Water formed
by slow mixing of Antarctic Bottom Water, North
Atlantic Deep Water advected from the North Atlantic
Ocean, and Intermediate Water from depths of less
than 1000 m (Tomczak and Godfrey, 1994). In the
North Pacific, much of the Deep Water may have last
contacted the atmosphere and taken up oxygen more
than 1000 years ago; as a consequence, this water
mass has relatively low levels of oxygen (although
typically not low enough to be biologically stressful).
Between depths of 500 m and 1000 m, the Pacific
is filled with Intermediate Water formed in either
the Antarctic or Arctic polar frontal regions, which
occur at roughly 60ºS and 40ºN, respectively. These
intermediate waters meet and upwell near the equator,
and are characterized by relatively low salinity and
temperatures that are warm (>3ºC) by deep-sea standards (Tomczak and Godfrey, 1994). In the northern
hemisphere, the intermediate waters are often formed
by subsurface mixing (i.e., they are not in atmospheric
contact during formation) and thus may be relatively
depleted in oxygen, contributing to formation of the
oxygen-minimum zone (see below, pp. 184–185).
KEY HABITAT VARIABLES AND THEIR REGIONAL
VARIATION IN THE PACIFIC
Several habitat variables play key roles in regulating
the nature and abundance of life on the deep-sea floor.
These include (1) substratum type (e.g., rocky versus
soft sediments), (2) near-bottom current velocities,
(3) bottom-water oxygen content, and (4) the vertical
flux of particulate organic carbon to the seafloor.
Substratum type
Substratum type controls, or at least is correlated