U.S. GLOBEC Rationale in the Northeast Pacific
On a wide range of time scales (from seasonal to interdecadal), there are strongly correlated signals in
physical and biological variables along the eastern boundaries of both gyres in the Northeast Pacific
Ocean (NEP)--the currents of the Coastal Gulf of Alaska (CGOA) and the California Current System
(CCS). Tide gauge and altimeter data suggest that the strengths of the boundary currents in these
gyres covary out of phase on annual and interannual time scales (the equatorward CCS strengthens
while the poleward and westward current in the CGOA weakens and vice versa [Chelton and Davis
1982]). Zooplankton volumes in the southern part of the CCS covary in phase with the interannual
changes in the CCS transport, although the mechanisms responsible for the covariance are not clear
(Chelton et al. 1982; Wickett 1967). On interdecadal time scales, there are data suggesting that
zooplankton and salmon both covary out of phase in the two boundary currents (Roemmich and
McGowan 1995; Brodeur and Ware 1992; Francis and Sibley 1991). Sardine in the CCS also covary
in phase with salmon in the CGOA, but out of phase with salmon in the CCS (Kawasaki 1992). The
interdecadal fluctuations of these populations, and others (Beamish, 1993), coincide with basin-scale
physical changes in atmospheric forcing and surface ocean conditions (temperature, mixed-layer
depth), although again the mechanisms responsible for the covariances are not known.
A focus of the first goal is to better understand the mechanism(s) responsible for the covarying, but
out of phase, production dynamics of zooplankton and fish of the CGOA and CCS ecosystems. The
target fish species for U.S. GLOBEC studies in the NEP are salmon. Salmon were selected due to the
economic impact of changes in salmon abundance and because their populations vary concident with
climate variability (Francis and Hare 1994). Zooplankton are important as indicators of the
productivity of the coastal ecosystem. Moreover, zooplankton are directly linked to salmon as their
prey, and indirectly by being alternate prey for some salmon predators (e.g., pollock, hake, some
birds). Thus, the target species for process studies in the coastal regions of both gyres are the juvenile
salmon and the dominant crustacean zooplankton (copepods and euphausiids) upon which salmon and
other predators in the ecosystem rely. While the process studies will focus on these species, other
elements of the program (modeling, retrospective analysis, monitoring) can address other species that
could elucidate NEP ecosystem changes in response to climate change.
- To understand the effects of climate variability and climate change on the distribution, abundance
and production of marine animals (including salmon and other commercially important living marine
resources) in the eastern North Pacific.
- To embody this understanding in diagnostic and prognostic models, capable of elucidating
ecosystem dynamics and responses on a range of time scales, including major climatic fluctuations.
- Production regimes in the Coastal Gulf of Alaska and California Current System covary, and are
coupled through atmospheric and ocean forcing.
- Spatial and temporal variability in mesoscale circulation constitutes the dominant physical
forcing on zooplankton biomass, production, distribution, species interactions, and retention and loss
in coastal regions.
- Ocean survival of salmon is primarily determined by survival of the juveniles in coastal
regions, and is affected by interannual and interdecadal changes in physical forcing and by changes in
ecosystem food web dynamics.
U.S. GLOBEC will study the effects of past and present climate variability on the population ecology
and population dynamics of marine biota and living marine resources, and use this information as a
proxy for how the ecosystems of the eastern North Pacific may respond to future global climate
change. The program plans to use the strong temporal variability in the physical and biological signals
to examine the biophysical mechanisms through which zooplankton and salmon populations respond
to physical forcing and biological interactions in the coastal regions of the two gyres. Annual and
interannual variability will be studied directly through monitoring activities (over a 5-7 year period)
and detailed process studies (over a 5 year period); variability at longer time scales will be examined
through retrospective analysis of directly measured and proxy data. Coupled bio-physical models of
the ecosystems of these regions will be developed and tested using the process studies and data
collected from the monitoring programs, then further tested and improved by hindcasting selected
retrospective data series.
Process studies in the NEP will focus on the causes of salmon mortality in the nearshore region during
the first part of their ocean residence, and will include investigations of bottom-up (zooplankton
production, salmon diet) and top-down interactions (predation by other fish, birds, and mammals).
The geographic locations for the studies will include three types of environments: 1) the predominantly
downwelling environment of the CGOA (surface convergence toward shore); 2) the moderate
upwelling environment off Oregon/Washington (Region I of the CCS, characterized by surface
divergence from shore with a nearly linear alongshore jet that may bar movement offshore but increase
movement alongshore); and 3), the strongly upwelling environment off northern/central California
(Region II of the CCS, characterized by surface divergence from shore with a complex meandering jet
and eddy system that may transport organisms far offshore).
Monitoring and retrospective components of the Northeast Pacific U.S. GLOBEC program will make
use of a broader suite of species than the process studies, especially focusing on species that might
serve as indicators of ecosystem variability in the boundary currents. Examples of such indicators are
the small pelagic fishes and nearshore benthic invertebrates. Population sizes of small pelagic fishes
have been documented to covary interannually and interdecadally with changes in the physical
environment. These relationships can be studied using fishery records and proxy estimates of
abundance recorded in anoxic sediments. Thus, small pelagic fishes are prime candidates for inclusion
in retrospective studies. Salmon ocean survival (a component important in determining year-class
strength) is believed to be determined during their earliest marine phase in the nearshore region. This
is also the region where mortality of benthic invertebrate planktonic larvae affects their rates of
successful settlement back to suitable nearshore adult habitat. Thus, nearshore settlement of benthic
invertebrates from the plankton, which can be monitored inexpensively at shore (intertidal) sites, could
provide finely resolved estimates of spatial and temporal variability in nearshore conditions--including
physical processes (transport, near-shore retention) and biological processes (growth)--important to
salmon growth and survival. The details of the mechanisms causing variable growth and mortality of
benthic invertebrate larvae, holozooplankton, and juvenile salmon need to be better understood in
terms of nearshore transports, mixing dynamics, production and food-web relations. In addition to
examining a broader suite of species, monitoring and retrospective studies should also examine a
wider range of geographic regions in order to encompass basin-scale (retrospective and monitoring)
and multi-decadal (retrospective) climatic processes.
Modeling is a central element of the U.S. GLOBEC NEP program and should also encompass the
broadest suite of species and geographic regions. At the largest scales, models must capture the
basin-scale interannual and interdecadal climate fluctuations, and should reproduce the differential
biological responses (inverse phasing) of the salmon and zooplankton populations and production in
the northern (CGOA) and southern (CCS) domains. Regional models of the boundary currents must
include details of the coastal circulation and biophysical interactions, with connections to the
basin-scale fluctuations. Models are also needed to predict salmon growth and survival during their
early ocean phase, emphasizing the role of ocean conditions, productivity and predator abundances in
determining the year class strength on interannual and longer time scales--i.e., to provide a foundation
for the prediction of salmon recruitment and, ultimately, better management of sustainable salmon
harvests under "non-steady state" ocean conditions.