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Chapter 11: The Pacific Ocean
Hemisphere in both oceans. This is, again in a general sense, the zone of winter rather
than spring blooms (McGowan and Williams, 1973; Banse and English, 1993), if indeed
the term bloom is relevant to such very weak chlorophyll enhancement as occurs.
Perhaps most important, we must accommodate the fact that, more strongly than in
the other oceans, Pacific circulation exists in two modes depending on the interannual
variability of trade-wind stress (see Chapter 6). During El Niño-Southern Oscillation
(ENSO) events, when trades weaken and are replaced by westerlies at low latitudes in
the western Pacific, the heat balance of the entire ocean at low latitudes is perturbed
for periods of a few months to 1–2 years. Here, for convenience, we regard this as the
anomalous condition and consider the normal condition to be that obtaining when trade
winds are well developed. The between-year, ENSO-scale alternation between the two
states resembles in many important ways the seasonal response of the tropical Atlantic to
between-season changes in trade-wind stress. This difference between the two oceans is
a consequence of their different zonal dimensions (Philander and Chao, 1991; Philander
and Pacanowski, 1981; Philander, 1985), a fact that has important consequences for
their dynamic biogeography (Longhurst, 1993). We shall encounter reports of long-term
alternations of state in circulation and ecosystem structure more commonly here than in
the other oceans.
The provinces into which it is useful to partition the tropical eastern Pacific during
normal conditions—viz., the Pacific Equatorial Countercurrent (PEEC), Pacific Equatorial
Divergence (PEQD), and North Pacific Tropical Gyre (NPTG) provinces—lose their
defining characteristics partially or completely during an ENSO event. During such
periods, rather uniform conditions with a deeper, warmer mixed layer obtain across the
whole region and I shall refer to this partition, when convenient, as the WARM-ENSO
Province, while recognizing its ephemeral nature and intermittent manifestation.
Because of the dimensions and hence global importance of the Pacific Ocean for
many issues that have evolved over the years, from its fisheries’ potential to oceanatmosphere interactions, climate control, and global carbon fluxes, we are fortunate that
it has attracted at least its fair share of oceanographic effort. We are also fortunate that
much of this work has been centrally planned (and peer-reviewed in the planning) so that
the issues of the day and—more important from our point of view—the key scientific
questions have had a chance of being answered.
Much of this work has been multinational and multiship, an increasingly important
aspect in recent years because the very extensive explorations by Soviet ships, which were
characteristic of Pacific exploration in earlier decades, have unfortunately now almost
ceased. Quite large regions of the ocean have been studied in a systematic way, along
preplanned grids of stations, repeated seasonally where required. Because of the planned
nature of much of the work that has been undertaken, the most important data sets are
already generally available through national data networks.
One of the minor consequences of all this effort is the fact that it is in the Pacific
Ocean that we can best appreciate the gross distribution patterns in the biogeography
of pelagic biota. Here, one has the impression that they have room to breathe and are
much more readily associated with regional oceanography than in the other oceans where
the current systems are less rectilinear, or ideal. Perhaps the maps of John McGowan
(1971) show this best. Here we see superimposed envelopes of distributions of groups of
species of pelagic organisms—plankton to tuna—having subarctic, transitional, central,
and equatorial distributions that, as we shall find, are in general agreement with the
conclusions we reach here on quite different grounds.
A recent multiauthored and on-line publication of PICES reviews the ecology of all
the major regional ecosystems of the North Pacific, but particularly from the point of
view of their between-year and decadal changes of state. The authors assume a knowledge
of the internal structure of each regional ecosystem, and document the changes that have
Chapter 11: The Pacific Ocean
Hemisphere in both oceans. This is, again in a general sense, the zone of winter rather
than spring blooms (McGowan and Williams, 1973; Banse and English, 1993), if indeed
the term bloom is relevant to such very weak chlorophyll enhancement as occurs.
Perhaps most important, we must accommodate the fact that, more strongly than in
the other oceans, Pacific circulation exists in two modes depending on the interannual
variability of trade-wind stress (see Chapter 6). During El Niño-Southern Oscillation
(ENSO) events, when trades weaken and are replaced by westerlies at low latitudes in
the western Pacific, the heat balance of the entire ocean at low latitudes is perturbed
for periods of a few months to 1–2 years. Here, for convenience, we regard this as the
anomalous condition and consider the normal condition to be that obtaining when trade
winds are well developed. The between-year, ENSO-scale alternation between the two
states resembles in many important ways the seasonal response of the tropical Atlantic to
between-season changes in trade-wind stress. This difference between the two oceans is
a consequence of their different zonal dimensions (Philander and Chao, 1991; Philander
and Pacanowski, 1981; Philander, 1985), a fact that has important consequences for
their dynamic biogeography (Longhurst, 1993). We shall encounter reports of long-term
alternations of state in circulation and ecosystem structure more commonly here than in
the other oceans.
The provinces into which it is useful to partition the tropical eastern Pacific during
normal conditions—viz., the Pacific Equatorial Countercurrent (PEEC), Pacific Equatorial
Divergence (PEQD), and North Pacific Tropical Gyre (NPTG) provinces—lose their
defining characteristics partially or completely during an ENSO event. During such
periods, rather uniform conditions with a deeper, warmer mixed layer obtain across the
whole region and I shall refer to this partition, when convenient, as the WARM-ENSO
Province, while recognizing its ephemeral nature and intermittent manifestation.
Because of the dimensions and hence global importance of the Pacific Ocean for
many issues that have evolved over the years, from its fisheries’ potential to oceanatmosphere interactions, climate control, and global carbon fluxes, we are fortunate that
it has attracted at least its fair share of oceanographic effort. We are also fortunate that
much of this work has been centrally planned (and peer-reviewed in the planning) so that
the issues of the day and—more important from our point of view—the key scientific
questions have had a chance of being answered.
Much of this work has been multinational and multiship, an increasingly important
aspect in recent years because the very extensive explorations by Soviet ships, which were
characteristic of Pacific exploration in earlier decades, have unfortunately now almost
ceased. Quite large regions of the ocean have been studied in a systematic way, along
preplanned grids of stations, repeated seasonally where required. Because of the planned
nature of much of the work that has been undertaken, the most important data sets are
already generally available through national data networks.
One of the minor consequences of all this effort is the fact that it is in the Pacific
Ocean that we can best appreciate the gross distribution patterns in the biogeography
of pelagic biota. Here, one has the impression that they have room to breathe and are
much more readily associated with regional oceanography than in the other oceans where
the current systems are less rectilinear, or ideal. Perhaps the maps of John McGowan
(1971) show this best. Here we see superimposed envelopes of distributions of groups of
species of pelagic organisms—plankton to tuna—having subarctic, transitional, central,
and equatorial distributions that, as we shall find, are in general agreement with the
conclusions we reach here on quite different grounds.
A recent multiauthored and on-line publication of PICES reviews the ecology of all
the major regional ecosystems of the North Pacific, but particularly from the point of
view of their between-year and decadal changes of state. The authors assume a knowledge
of the internal structure of each regional ecosystem, and document the changes that have