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Physical and biological conditions and processes in the northeast Pacific Ocean
Progress in Oceanography 53 (2002) 105–114 www.elsevier.com/locate/pocean
Editorial
Physical and biological conditions and processes in the northeast Pacific Ocean
Physical and biological variables along the eastern margin of the Pacific in the Northern Hemisphere exhibit strong correlations on a wide range of time scales, ranging from seasonal to interdecadal (Ware & Thomson, 2000; U.S. GLOBEC, 1996). The coastal region extending from the Aleutians to Baja encompasses the eastern domain of two large oceanic gyres (the subtropical North Pacific gyre; subarctic Alaskan gyre), which are separated by the North Pacific Current (West Wind Drift). As the North Pacific Current nears the coast of North America it diverges into a northward flowing current (Alaska Current) and a southward flowing current (California Current). We refer to this region as the Northeast Pacific (NEP) (Fig. 1). The physical structure, transport processes, and biology of the NEP respond strongly to forcings at several time/space scales. For example, El Nin˜o–Southern Oscillations (ENSOs) can result in large interannual changes in sea surface temperature, mixed layer depth, and transport processes for both coastal and offshore regions of North America. At longer time scales, shifts in the position and intensity of atmospheric pressure systems in the Northern Hemisphere create ‘regime shifts’ that dramatically alter ocean structure and physics in the NEP (Fig. 2). Biological responses at several trophic levels to interdecadal or ENSO variability have been recognized in both the California Current System (herafter, CCS) and the Alaska Current System. At the interdecadal time scales, perhaps the best documented biological responses are in the abundance and distribution of fish populations, like the salmonids (see Bailey et al., 1995; Beamish, 1993, collection of papers in 1995; Beamish & McFarlane, 1989; Brodeur & Ware, 1995; Francis & Hare, 1994; Hare & Francis, 1995) and small pelagic fish, such as sardines and anchovies (Kawasaki, 1992; Lluch-Belda et al., 1989) (Fig. 3). Polovina and his colleagues (Polovina et al., 1994; Polovina, Mitchum, & Evans, 1995) (1) documented changes in North Pacific winter and spring mixed layer depth and temperature related to the regime shift of 1976–77; (2) used a plankton production model to suggest that these shifts resulted in higher primary and secondary production in both the subarctic and subtropical gyres; and, (3) documented concurrent increases in the productivity at higher trophic levels (lobsters, birds, seals) in the Hawaiian archipelago. Mackas, Goldblatt, and Lewis (1998) observed continuous (but not stepwise) shifts during the 1970s to 1990s to earlier biomass peaks of Neocalanus plumchrus, one of the dominant copepod species of the subarctic Pacific, possibly resulting from warmer ocean conditions which favored survival of individuals developing earlier in the year. The biological and ecological effects of interdecadal variability of climate forcing, and ocean response, are to some extent geographically specific. Changes in the basin forcing and circulation may impact marine populations in different areas of the NEP in contrasting ways. Francis and Sibley (1991) showed that 0079-6611/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 7 9 - 6 6 1 1 ( 0 2 ) 0 0 0 2 6 - 5
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Fig. 1.
Editorial / Progress in Oceanography 53 (2002) 105–114
Fisheries production domains and general circulation in the NEP Ocean. (Redrawn from Ware & McFarlane, 1989.)
decadal, or longer, periods of high CCS coho abundance tended to be periods of low Gulf of Alaska pink salmon abundance, and vice versa. Fig. 3 shows that total salmon catch (an estimate of salmon population abundance) in the northern realm of the NEP (subarctic gyre or coastal Gulf of Alaska, hereafter CGOA) tends to vary inversely with salmon catches from the California Current region to the south, but in-phase with populations of small pelagic fishes in the CCS. The paper in this issue by Botsford and Lawrence examined more critically the patterns of covariability between salmonid species both within and across regions in the NEP. Similar opposite phase cycles are observed in zooplankton biomass in the Alaska Stream and California Current (Brodeur & Ware, 1992; Roemmich & McGowan, 1995). These out-ofphase population dynamics may be a direct response to eastern boundary current intensities of these two gyres that covary out of phase on annual, interannual and longer time scales. At interannual time scales, Chelton and Davis (1982) proposed that when the equatorward California Current strengthens, the poleward Alaska current weakens and vice versa. Moreover, zooplankton volumes (e.g., biomass) in the Southern California Bight were found to covary in-phase with interannual changes in the California Current southward transport, although the mechanisms responsible for the covariance are unknown (Chelton, Bernal, & McGowan, 1982; Wickett, 1967). The two papers by Strub and James in this issue use satellite altimeterderived circulation fields to examine seasonal and interannual (e.g., El Nin˜ o effects) covariability and linkages between these two gyres in the North Pacific. The most dominant source of interannual variability in the Pacific Ocean is the El Nin˜ o–Southern Oscil-
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Fig. 2. February (top) and August (bottom) SST differences between 1977–86 and 1966–75. Large positive changes (warmer water in more recent regime are red; cooler water is blue) are widespread along the west coast during winter and summer, with largest differences during winter. (Figure courtesy of Franklin Schwing.)
lation (ENSO). ENSO effects begin as abnormal conditions at the equator, but during strong events the impacts of ENSO can propagate poleward to the extratropics. The best documented, strong ENSOs (1982– 83, 1997–98) generated clear physical and/or biological signals in the far northern regions of the NEP (see Mackas & Galbraith, in press; Pearcy, in press; Peterson, Keister, & Feinberg, in press; papers in Wooster & Fluharty, 1985). During the El Nin˜ os of 1982–83 and 1997–98, water temperature in the Northern Gulf of Alaska (Royer, 1985; Royer, pers. comm.) warmed significantly. At lower latitudes (off Oregon, California), coastal water temperature and sea levels were high, and poleward flow anomalously high for several months during each of these events (Huyer & Smith, 1985; Huyer, Smith, & Fleischbein, in press). Changes in nearshore ocean physics and the intensity of poleward flows along the west coast can have
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Fig. 3. (Top) Salmon abundance in northern (Alaska) and southern (WA-OR-CA) regions of the northeast Pacific. (Alaska data are from the Alaska Dept. of Fish and Game records of commercial salmon harvest. WA-OR-CA data are from records compiled by Shepard, Shepard, & Argue, 1985, updated with more recent catches through 1990. Post-1990 harvest of salmon was restricted by regulation, so are not shown.) (Bottom) Historical catches in the sardine fishery (bottom) of Japan, California, and Peru–Chile. (Modified from Kawasaki, 1992, updated with more recent data.) Note different ordinate scales.
significant impacts on the ecosystem. Some of these effects probably arise as a result of local processes, such as decreased or less effective injection of nutrients into the euphotic zone during upwelling. Others may be caused by more remote processes, such as the alongshore advection of species with normally southern affinities to more northern regions. Zooplankton abundance and composition off Oregon and British Columbia change during strong El Nin˜ os, during which either southern or offshore species become more dominant components, whereas normal boreal shelf species are reduced in abundance (Mackas & Galbraith, in press; Miller, Batchelder, Brodeur, & Pearcy, 1985; Peterson et al., in press). Southern species rarely encountered off Oregon can be advected from the south by anomalous coastal currents during an El Nin˜ o. This was the case for the euphausiid, Nyctiphanes simplex (Peterson et al., in press) in 1997–98, and for numerous coastal fish species in 1983 (Pearcy & Schoener, 1987). More than a decade ago, the U.S. Global Ocean Ecosystems Dynamics (U.S. GLOBEC) program began planning research programs in several ocean ecosystem types, including shelf–bank systems, eastern bound-
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ary currents and sea–ice systems. U.S. GLOBEC is a long-term research initiative organized by the oceanographic and fisheries communities, and supported principally by the National Science Foundation, and the Coastal Ocean Program within the National Oceanic and Atmospheric Administration. The principal aim of the program is to understand how climate variability affects the abundances, distribution, and production of animals in the sea. Through extensive discussions and workshops, an implementation plan was developed for a Northeast Pacific (NEP) research program (U.S. GLOBEC, 1996), which encompasses both an upwelling eastern boundary current (within the California Current System), and a buoyancy driven eastern boundary current (in the Coastal Gulf of Alaska). Recent reviews of coastal ocean processes of the CCS and CGOA can be found in Hickey (1998) and Royer (1998), respectively. The NEP was selected as a region for U.S. GLOBEC investigations because it (1) experiences strong interannual and interdecadal variability in ocean conditions, (2) provides a strong contrast between wind-driven upwelling (CCS) and wind/buoyancy driven downwelling (CGOA) systems, and (3) is home to numerous economically important marine resources. The next ten years will be an exciting time for oceanography of the coastal Northeast Pacific Ocean (NEP), because in addition to U.S. GLOBEC plans in the NEP, several other large observational programs (CoOP, EVOS, CLIVAR, PISCO) have targeted the NEP for regional studies, complementing other ongoing long-term studies (CalCOFI, MBARI transect line, Vancouver Island shelf) (Table 1; Fig. 4). These investigations will provide a more complete understanding of the functioning of this dynamic biophysical system. Interest in the NEP region has been stimulated by retrospective analysis of long-term data sets that indicate strongly correlated seasonal-to-interdecadal signals in physical and biological variables along the boundaries of both gyres in the Northeast Pacific Ocean (see above). The core goals of the U.S. GLOBEC NEP program are threefold: (1) to examine how the productivities of the CGOA and CCS covary as they respond to atmospheric and ocean forcing at several time and space scales; (2) to examine specifically the importance of mesoscale (20s–100s km) spatial variability in controlling zooplankton biomass, production, species distributions, vital rates, and retention and loss in coastal regions; and (3) to determine how interannual and interdecadal changes in physical forcing and ecosystems food web dynamics affect survival of juvenile salmon during their period of residence in the coastal ocean. The program focuses on the linkage between large-scale climate forcing, mesoscale physical variability, and biological productivity, with a special emphasis on salmon and their prey and predators. U.S. GLOBEC has specifically selected similar target species (salmon, euphausiids, copepods) and physical processes (mesoscale dynamics, cross-shelf transport, local versus remote production) in the CGOA and CCS so that the results of the investigations can be compared across the eastern North Pacific. Addressing questions about the physical and biological impacts of climate change and variability requires data spanning long time horizons—from the past, present and future. Each of these is a component of U.S. GLOBEC studies. Past variability and change are examined through retrospective analysis of existing datasets and the development of new data sets and proxies for marine conditions. Present time conditions and biophysical interactions are examined through a combination of sustained observations and intensive, shorter duration, process-oriented field studies. Finally, the need to understand future variability and change provides the rationale for initiating frequent, sustained monitoring of the ecosystem at a few selected sites. U.S. GLOBEC studies, alone, are incapable of developing the data sets, process studies, long-term observations and models needed to understand the complex interactions of forcing on ocean conditions and nearcoast ecosystems. Consequently, modeling and synthesis activities will integrate the results from research, monitoring, and retrospective activities (from GLOBEC and other programs on the west coast; see Table 1), so that the consequences of climate variability on coastal ecosystems can be evaluated and, perhaps, projected. Toward that end, the U.S. GLOBEC program has initiated three phases of research in the NEP ecosystem. The first phase supported initial modeling, retrospective and monitoring studies within the region as a whole. The second and third phases are to continue the initial activities, but also specifically to begin
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Table 1 Selected long-term and regional scientific programs in the Northeast Pacific Program
Time period
Region
GLOBEC
1997–2004
CCS & CGOA
California Cooperative Oceanic Fisheries Investigation (CalCOFI) MBARI Moorings and Transect Surveys Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO)
1951–present
Pacific Northwest Coastal Ecosystems Research Study (PNCERS)
ca. 1997–2001
Vancouver Island Shelf
1985–present
Line P
1949–present
Exxon Valdez Oil Spill (EVOS) Sound Ecosystem Assessment (SEA) EVOS Gulf Ecosystem Monitoring (GEM) program
1993–1998
1989–present 1998–2002
2003–? (possibly 100 years)
Coastal Ocean Processes 2001–2004 (CoOP) Coastal Ocean Advances in Shelf Transport (COAST) CoOP Wind Events and Shelf 2000–2004 Transport (WEST) Climate Variability and Predictability (CLIVAR)
1995–2010
Argo
2001–?
Investigaciones Mexicanas de 1997–present la Corriente de California (IMECOCAL)
Focus
Climate forcing of ocean physics and impacts on coastal ecosystems California Current, esp. Southern Hydrography and plankton and California Bight fish distributions and composition Monterey Bay Hydrography, plankton biogeochemistry U.S. West Coast; California Hydrography, marine Current from Oregon to Southern meroplankton distribution; larval California recruitment, and adult benthic invertebrates U.S. West Coast, esp. Willapa Research and outreach on Bay and Grays Harbor, WA, and coastal management issues Tillamook Bay and Coos Bay, OR Shelf West of Vancouver Island Hydrography, nutrients, plankton, birds Transect from Juan de Fuca Strait Hydrography, nutrients, plankton to Ocean Station Papa Prince William Sound, AK Hydrography, productivity, and trophic ecology of marine organisms Prince William Sound, Cook Inlet Hydrography, productivity, and adjacent shelf ecosystem, AK diversity, trophic ecology of zooplankton to birds and mammals Nearshore Oregon shelf Atmospheric forcing, ecosystem hydrography, productivity, cross-shelf transport No. California; Pt. Arena to San Francisco Bay
Atmospheric forcing, ocean response and trophic responses; cross-shelf transport Worldwide; esp.Pacific Basin Climate variability and Extended Climate Study (PBECS) predictability at seasonal to centennial time scales Worldwide; extensive coverage in Heat and freshwater storage and NEP transport in oceanic realm Baja California’s west coast, Climate change impacts on Southern part of the California hydrography, zooplankton, Current System ichthyoplankton and pelagic fish
focused process-oriented field research in the CCS and CGOA, respectively. The 12 papers in this issue present some results from the modeling, retrospective and long-term observations initiated in Phase I. Eight of the contributions in this issue use existing long-term data sets or proxies to examine temporal variability in the NEP ecosystem. Schwing et al. and Mendelssohn and Schwing examine large scale climatological patterns in the eastern Pacific of both the Northern and Southern Hemispheres. Two papers by Strub and James document seasonal and interannual variability, including the response of large-scale surface
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Fig. 4. Map of selected recent, ongoing, or planned ocean research programs in the Northeast Pacific.
circulation to a strong El Nin˜ o. The longest-duration biological data set for the eastern North Pacific is the 50-year record of zooplankton abundance collected by the CalCOFI program. Zooplankton volumes from that time series have been used to document the dramatic 3- to 4-fold decline in zooplankton biomass that occurred off Southern California, beginning at approximately the time of the mid 1970s warming event in the California Current System (Roemmich & McGowan, 1995). To date, there has been little investigation of zooplankton species compositional changes during this period of declining overall biomass. Rebstock and her colleagues are examining this decline, but first she addresses the question of whether a 1978 change in the zooplankton sampling gear had an effect on species-specific capture efficiency. Rebstock reports that the sampling gear change did not introduce species specific biases in sampling efficiency, suggesting that compositional changes that occur during the CalCOFI sampling period were responses to variable or changing ocean conditions. Satterfield and Finney use stable isotope analysis to examine the late 1990s trophic status of five Pacific salmon species, and use isotope analysis of sockeye scales from layered lake sediments spanning 30 years to retrospectively document shifts in trophic level, shift in foraging region, or changes in the isotopic composition at the base of the food web (e.g., a change in ocean conditions). Doyle and her co-authors document regional variations in ichthyoplankton assemblages in the Northeast Pacific Ocean, including the Bering Sea, Northern Gulf of Alaska and California Current. Botsford and Lawrence re-examine the historical records of salmon abundance in the Northeast Pacific, and find that the story is not quite as simple as “salmon populations in the CCS and CGOA covary out-of-phase”.
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Chinook salmon populations remained relatively stable in both the CCS and CGOA, whereas Coho salmon and Dungeness crab populations in the CCS declined during the 1970–80s, generally indicating an adverse response to the generally warmer ocean conditions. The results of two modeling studies are reported. Batchelder et al. use a model to explore the interaction of ontogenetically and physiologically variable diel vertical migration and nearshore cross-shelf flows. They report that nearshore retention, survival and overall population abundance were strongly controlled by the interaction of diel vertical migration and depth varying transports. Hermann et al. describe the coupling of a regional circulation model with a global circulation model, evaluate the impacts of subtidal and tidal forcing, and compare the regional model output to selected oceanographic observations. Finally, there are two papers reporting results from Long-Term Observation Program (LTOP) studies implemented by U.S. GLOBEC off Northern California and Oregon. A paper by Hill and Wheeler documents the spatial variability of organic carbon and nitrogen in different water masses in the region. Peterson and Keister compare abundance, distribution and species composition of zooplankton north and south of a prominent cape, during two years of contrasting ocean conditions. These studies form the foundation for the investigations scheduled in the next decade in the Northeast Pacific Ocean. All of the major types of investments undertaken by U.S. and international GLOBEC programs are covered. Specifically, these preliminary projects provide a first look at various aspects that will be more completely described by data collected in this and other programs in the NEP—a region that seems especially responsive to variable climate forcing.
Acknowledgements This is contribution #194 of the U.S. GLOBEC program, jointly funded by the National Science Foundation and National Oceanic and Atmospheric Administration. The writing of this paper was supported under NSF Grants OCE-0003273 and OCE-0002047. Harold P. Batchelder, College of Oceanic and Atmospheric Science, Oregon State University, 104 Ocean Admin Building, Corvallis, OR 97331-5503, USA E-mail address: [email protected] Thomas M. Powell, University of California, Department of Integrative Biology, 3060 Valley Life Sciences Building, Berkeley, CA 94720-3140, USA PII: S0079-6611(02)00026-5
References Bailey, K. M., Macklin, S. A., Reed, R. K., Brodeur, R. D., Ingraham, W. J., Piatt, J. F., Shima, M., Francis, R. C., Anderson, P. J., Royer, T. C., Hollowed, A. B., Somerton, D. A., & Wooster, W. S. (1995). ENSO events in the northern Gulf of Alaska, and effects on selected marine fisheries. CalCOFI Reports, 36, 78–96. Beamish, R. J. (1993). Climate and exceptional fish production off the west coast of North America. Canadian Journal of Fisheries and Aquatic Sciences, 50, 2270–2291. Beamish, R.J. (Ed.). (1995). Climate change and northern fish populations. Canadian Special Publication of Fisheries and Aquatic Sciences, 121. (739 pp.).
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Beamish, R.J., & McFarlane, G.A. (Eds.). (1989). Effects of ocean variability on recruitment and an evaluation of parameters used in stock assessment models. Canadian Special Publication of Fisheries and Aquatic Sciences, 108. (379 pp.). Brodeur, R. D., & Ware, D. M. (1992). Long-term variability in zooplankton biomass in the subarctic Pacific Ocean. Fisheries Oceanography, 1, 32–38. Brodeur, R. D., & Ware, D. M. (1995). Interdecadal variability in distribution and catch rates of epipelagic nekton in the Northeast Pacific Ocean. In R. J. Beamish (Ed.), Climate change and northern fish populations (pp. 329–356). Canadian Special Publication on Fisheries and Aquatic Sciences, 121. Chelton, D. B., Bernal, P. A., & McGowan, J. A. (1982). Large-scale interannual physical and biological interaction in the California Current. Journal of Marine Research, 40, 1095–1125. Chelton, D. B., & Davis, R. E. (1982). Monthly mean sea-level variability along the west coast of North America. Journal of Physical Oceanography, 12, 757–784. Francis, R. C., & Hare, S. R. (1994). Decadal-scale regime shifts in the large marine ecosystems of the northeast Pacific: a case for historical science. Fisheries Oceanography, 3, 279–291. Francis, R. C., & Sibley, T. H. (1991). Climate change and fisheries: what are the real issues? The Northwest Environmental Journal, 7, 295–307. Hare, S. R., & Francis, R. C. (1995). Climate change and salmon production in the northeast Pacific Ocean. In R. J. Beamish (Ed.), Climate change and northern fish populations (pp. 357–372). Canadian Special Publication of Fisheries and Aquatic Sciences, 121. Hickey, B. M. (1998). Coastal oceanography of western North America from the tip of Baja California to Vancouver Island. In A. R. Robinson, & K. H. Brink (Eds.), (pp. 345–393). The Sea, vol. 11. New York: John Wiley & Sons. Huyer, A., & Smith, R. L. (1985). The signature of El Nin˜ o off Oregon, 1982–83. Journal of Geophysical Research, 90, 7133–7142. Huyer, A., Smith, R. L., & Fleischbein, J. (in press). The coastal ocean off Oregon and northern California during the 1997–98 El Nin˜ o. Progress in Oceanography. Kawasaki, T. (1992). Mechanisms governing fluctuations in pelagic fish populations. South African Journal of Marine Science, 12, 873–879. Lluch-Belda, D., Crawford, R. J. M., Kawasaki, T., MacCall, A. D., Parrish, R. H., Swartzlose, R. A., & Smith, P. E. (1989). World wide fluctuations of sardine and anchovy stocks: the regime problem. South African Journal of Marine Science, 8, 195–205. Mackas, D. L., & Galbraith, M. (in press). Zooplankton community composition along the inner portion of Line P during the 1997– 98 El Nin˜ o event. Progress in Oceanography. Mackas, D. L., Goldblatt, R., & Lewis, A. G. (1998). Interdecadal variation in developmental timing of Neocalanus plumchrus populations at Ocean Station P in the subarctic North Pacific. Canadian Journal of Fisheries and Aquatic Sciences, 55, 1878–1893. Miller, C. B., Batchelder, H. P., Brodeur, R. D., & Pearcy, W. G. (1985). Response of zooplankton and ichthyoplankton off Oregon to the El Nin˜ o event of 1983. In W. S. Wooster, & D. L. Fluharty (Eds.), El Nin˜ o North (pp. 185–187). Seattle, WA: University of Washington. Pearcy, W. G. (in press). Effects of the 1997–98 El Nin˜ o on marine nekton off Oregon. Progress in Oceanography. Pearcy, W. G., & Schoener, A. (1987). Changes in the marine biota coincident with the 1982–83 El Nin˜ o in the northeastern subarctic Pacific Ocean. Journal of Geophysical Research, 92, 14417–14428. Peterson, W. T., Keister, J. E., & Feinberg, L. R. (in press). The effects of the 1997–99 El Nin˜ o/La Nin˜ a events on hydrography and zooplankton off the central Oregon coast. Progress in Oceanography. Polovina, J. J., Mitchum, G. T., & Evans, G. T. (1995). Decadal and basin-scale variation in mixed layer depth and the impact on biological production in the Central and North Pacific, 1960–88. Deep Sea Research, 42, 1701–1716. Polovina, J. J., Mitchum, G. T., Graham, N. E., Craig, M. P., DeMartini, E. E., & Flint, E. N. (1994). Physical and biological consequences of a climate event in the central North Pacific. Fisheries Oceanography, 3, 15–21. Roemmich, D., & McGowan, J. A. (1995). Climate warming and the decline of zooplankton in the California Current. Science, 267, 1324–1326. Royer, T. C. (1985). Coastal temperature and salinity anomalies in the northern Gulf of Alaska, 1970–84. In W. S. Wooster, & D. L. Fluharty (Eds.), El Nin˜ o North (pp. 185–187). Seattle, WA: University of Washington. Royer, T. C. (1998). Coastal processes in the northern North Pacific. In A. R. Robinson, & K. H. Brink (Eds.), (pp. 395–414). The Sea, vol. 11. New York: John Wiley & Sons. Shepard, M. P., Shepard, C. D., & Argue, A. W. (1985). Historic statistics of salmon production around the Pacific rim. Canadian Manuscript Report of Fisheries and Aquatic Sciences, 1819. (297 pp.). U.S. GLOBEC (1996). U.S. GLOBEC Northeast Pacific implementation plan, U.S. GLOBEC Report No. 17. Berkeley: University of California (60 pp.). Ware, D. M., McFarlane, G. A. (1989). Fisheries production domains in the Northeast Pacific Ocean. In R. J. Beamish, & G. A. McFarlane (Eds.) (pp. 359–379). Effects of ocean variability on recruitment and an evaluation of parameters used in stock assessment models. Canadian Special Publication of Fisheries and Aquatic Sciences, 108. Ware, D. M., & Thomson, R. E. (2000). Interannual to multidecadal timescale climate variations in the Northeast Pacific. Journal of Climate, 13, 3209–3220.
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Wickett, W. P. (1967). Ekman transport and zooplankton concentration in the North Pacific. Journal of the Fisheries Research Board of Canada, 24, 581–594. Wooster, W.S., & Fluharty, D.L. (Eds.). (1985). El Nin˜ o North. Seattle, WA: University of Washington (312 pp.).
Editorial
Physical and biological conditions and processes in the northeast Pacific Ocean
Physical and biological variables along the eastern margin of the Pacific in the Northern Hemisphere exhibit strong correlations on a wide range of time scales, ranging from seasonal to interdecadal (Ware & Thomson, 2000; U.S. GLOBEC, 1996). The coastal region extending from the Aleutians to Baja encompasses the eastern domain of two large oceanic gyres (the subtropical North Pacific gyre; subarctic Alaskan gyre), which are separated by the North Pacific Current (West Wind Drift). As the North Pacific Current nears the coast of North America it diverges into a northward flowing current (Alaska Current) and a southward flowing current (California Current). We refer to this region as the Northeast Pacific (NEP) (Fig. 1). The physical structure, transport processes, and biology of the NEP respond strongly to forcings at several time/space scales. For example, El Nin˜o–Southern Oscillations (ENSOs) can result in large interannual changes in sea surface temperature, mixed layer depth, and transport processes for both coastal and offshore regions of North America. At longer time scales, shifts in the position and intensity of atmospheric pressure systems in the Northern Hemisphere create ‘regime shifts’ that dramatically alter ocean structure and physics in the NEP (Fig. 2). Biological responses at several trophic levels to interdecadal or ENSO variability have been recognized in both the California Current System (herafter, CCS) and the Alaska Current System. At the interdecadal time scales, perhaps the best documented biological responses are in the abundance and distribution of fish populations, like the salmonids (see Bailey et al., 1995; Beamish, 1993, collection of papers in 1995; Beamish & McFarlane, 1989; Brodeur & Ware, 1995; Francis & Hare, 1994; Hare & Francis, 1995) and small pelagic fish, such as sardines and anchovies (Kawasaki, 1992; Lluch-Belda et al., 1989) (Fig. 3). Polovina and his colleagues (Polovina et al., 1994; Polovina, Mitchum, & Evans, 1995) (1) documented changes in North Pacific winter and spring mixed layer depth and temperature related to the regime shift of 1976–77; (2) used a plankton production model to suggest that these shifts resulted in higher primary and secondary production in both the subarctic and subtropical gyres; and, (3) documented concurrent increases in the productivity at higher trophic levels (lobsters, birds, seals) in the Hawaiian archipelago. Mackas, Goldblatt, and Lewis (1998) observed continuous (but not stepwise) shifts during the 1970s to 1990s to earlier biomass peaks of Neocalanus plumchrus, one of the dominant copepod species of the subarctic Pacific, possibly resulting from warmer ocean conditions which favored survival of individuals developing earlier in the year. The biological and ecological effects of interdecadal variability of climate forcing, and ocean response, are to some extent geographically specific. Changes in the basin forcing and circulation may impact marine populations in different areas of the NEP in contrasting ways. Francis and Sibley (1991) showed that 0079-6611/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 0 7 9 - 6 6 1 1 ( 0 2 ) 0 0 0 2 6 - 5
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Fig. 1.
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Fisheries production domains and general circulation in the NEP Ocean. (Redrawn from Ware & McFarlane, 1989.)
decadal, or longer, periods of high CCS coho abundance tended to be periods of low Gulf of Alaska pink salmon abundance, and vice versa. Fig. 3 shows that total salmon catch (an estimate of salmon population abundance) in the northern realm of the NEP (subarctic gyre or coastal Gulf of Alaska, hereafter CGOA) tends to vary inversely with salmon catches from the California Current region to the south, but in-phase with populations of small pelagic fishes in the CCS. The paper in this issue by Botsford and Lawrence examined more critically the patterns of covariability between salmonid species both within and across regions in the NEP. Similar opposite phase cycles are observed in zooplankton biomass in the Alaska Stream and California Current (Brodeur & Ware, 1992; Roemmich & McGowan, 1995). These out-ofphase population dynamics may be a direct response to eastern boundary current intensities of these two gyres that covary out of phase on annual, interannual and longer time scales. At interannual time scales, Chelton and Davis (1982) proposed that when the equatorward California Current strengthens, the poleward Alaska current weakens and vice versa. Moreover, zooplankton volumes (e.g., biomass) in the Southern California Bight were found to covary in-phase with interannual changes in the California Current southward transport, although the mechanisms responsible for the covariance are unknown (Chelton, Bernal, & McGowan, 1982; Wickett, 1967). The two papers by Strub and James in this issue use satellite altimeterderived circulation fields to examine seasonal and interannual (e.g., El Nin˜ o effects) covariability and linkages between these two gyres in the North Pacific. The most dominant source of interannual variability in the Pacific Ocean is the El Nin˜ o–Southern Oscil-
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Fig. 2. February (top) and August (bottom) SST differences between 1977–86 and 1966–75. Large positive changes (warmer water in more recent regime are red; cooler water is blue) are widespread along the west coast during winter and summer, with largest differences during winter. (Figure courtesy of Franklin Schwing.)
lation (ENSO). ENSO effects begin as abnormal conditions at the equator, but during strong events the impacts of ENSO can propagate poleward to the extratropics. The best documented, strong ENSOs (1982– 83, 1997–98) generated clear physical and/or biological signals in the far northern regions of the NEP (see Mackas & Galbraith, in press; Pearcy, in press; Peterson, Keister, & Feinberg, in press; papers in Wooster & Fluharty, 1985). During the El Nin˜ os of 1982–83 and 1997–98, water temperature in the Northern Gulf of Alaska (Royer, 1985; Royer, pers. comm.) warmed significantly. At lower latitudes (off Oregon, California), coastal water temperature and sea levels were high, and poleward flow anomalously high for several months during each of these events (Huyer & Smith, 1985; Huyer, Smith, & Fleischbein, in press). Changes in nearshore ocean physics and the intensity of poleward flows along the west coast can have
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Fig. 3. (Top) Salmon abundance in northern (Alaska) and southern (WA-OR-CA) regions of the northeast Pacific. (Alaska data are from the Alaska Dept. of Fish and Game records of commercial salmon harvest. WA-OR-CA data are from records compiled by Shepard, Shepard, & Argue, 1985, updated with more recent catches through 1990. Post-1990 harvest of salmon was restricted by regulation, so are not shown.) (Bottom) Historical catches in the sardine fishery (bottom) of Japan, California, and Peru–Chile. (Modified from Kawasaki, 1992, updated with more recent data.) Note different ordinate scales.
significant impacts on the ecosystem. Some of these effects probably arise as a result of local processes, such as decreased or less effective injection of nutrients into the euphotic zone during upwelling. Others may be caused by more remote processes, such as the alongshore advection of species with normally southern affinities to more northern regions. Zooplankton abundance and composition off Oregon and British Columbia change during strong El Nin˜ os, during which either southern or offshore species become more dominant components, whereas normal boreal shelf species are reduced in abundance (Mackas & Galbraith, in press; Miller, Batchelder, Brodeur, & Pearcy, 1985; Peterson et al., in press). Southern species rarely encountered off Oregon can be advected from the south by anomalous coastal currents during an El Nin˜ o. This was the case for the euphausiid, Nyctiphanes simplex (Peterson et al., in press) in 1997–98, and for numerous coastal fish species in 1983 (Pearcy & Schoener, 1987). More than a decade ago, the U.S. Global Ocean Ecosystems Dynamics (U.S. GLOBEC) program began planning research programs in several ocean ecosystem types, including shelf–bank systems, eastern bound-
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ary currents and sea–ice systems. U.S. GLOBEC is a long-term research initiative organized by the oceanographic and fisheries communities, and supported principally by the National Science Foundation, and the Coastal Ocean Program within the National Oceanic and Atmospheric Administration. The principal aim of the program is to understand how climate variability affects the abundances, distribution, and production of animals in the sea. Through extensive discussions and workshops, an implementation plan was developed for a Northeast Pacific (NEP) research program (U.S. GLOBEC, 1996), which encompasses both an upwelling eastern boundary current (within the California Current System), and a buoyancy driven eastern boundary current (in the Coastal Gulf of Alaska). Recent reviews of coastal ocean processes of the CCS and CGOA can be found in Hickey (1998) and Royer (1998), respectively. The NEP was selected as a region for U.S. GLOBEC investigations because it (1) experiences strong interannual and interdecadal variability in ocean conditions, (2) provides a strong contrast between wind-driven upwelling (CCS) and wind/buoyancy driven downwelling (CGOA) systems, and (3) is home to numerous economically important marine resources. The next ten years will be an exciting time for oceanography of the coastal Northeast Pacific Ocean (NEP), because in addition to U.S. GLOBEC plans in the NEP, several other large observational programs (CoOP, EVOS, CLIVAR, PISCO) have targeted the NEP for regional studies, complementing other ongoing long-term studies (CalCOFI, MBARI transect line, Vancouver Island shelf) (Table 1; Fig. 4). These investigations will provide a more complete understanding of the functioning of this dynamic biophysical system. Interest in the NEP region has been stimulated by retrospective analysis of long-term data sets that indicate strongly correlated seasonal-to-interdecadal signals in physical and biological variables along the boundaries of both gyres in the Northeast Pacific Ocean (see above). The core goals of the U.S. GLOBEC NEP program are threefold: (1) to examine how the productivities of the CGOA and CCS covary as they respond to atmospheric and ocean forcing at several time and space scales; (2) to examine specifically the importance of mesoscale (20s–100s km) spatial variability in controlling zooplankton biomass, production, species distributions, vital rates, and retention and loss in coastal regions; and (3) to determine how interannual and interdecadal changes in physical forcing and ecosystems food web dynamics affect survival of juvenile salmon during their period of residence in the coastal ocean. The program focuses on the linkage between large-scale climate forcing, mesoscale physical variability, and biological productivity, with a special emphasis on salmon and their prey and predators. U.S. GLOBEC has specifically selected similar target species (salmon, euphausiids, copepods) and physical processes (mesoscale dynamics, cross-shelf transport, local versus remote production) in the CGOA and CCS so that the results of the investigations can be compared across the eastern North Pacific. Addressing questions about the physical and biological impacts of climate change and variability requires data spanning long time horizons—from the past, present and future. Each of these is a component of U.S. GLOBEC studies. Past variability and change are examined through retrospective analysis of existing datasets and the development of new data sets and proxies for marine conditions. Present time conditions and biophysical interactions are examined through a combination of sustained observations and intensive, shorter duration, process-oriented field studies. Finally, the need to understand future variability and change provides the rationale for initiating frequent, sustained monitoring of the ecosystem at a few selected sites. U.S. GLOBEC studies, alone, are incapable of developing the data sets, process studies, long-term observations and models needed to understand the complex interactions of forcing on ocean conditions and nearcoast ecosystems. Consequently, modeling and synthesis activities will integrate the results from research, monitoring, and retrospective activities (from GLOBEC and other programs on the west coast; see Table 1), so that the consequences of climate variability on coastal ecosystems can be evaluated and, perhaps, projected. Toward that end, the U.S. GLOBEC program has initiated three phases of research in the NEP ecosystem. The first phase supported initial modeling, retrospective and monitoring studies within the region as a whole. The second and third phases are to continue the initial activities, but also specifically to begin
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Table 1 Selected long-term and regional scientific programs in the Northeast Pacific Program
Time period
Region
GLOBEC
1997–2004
CCS & CGOA
California Cooperative Oceanic Fisheries Investigation (CalCOFI) MBARI Moorings and Transect Surveys Partnership for Interdisciplinary Studies of Coastal Oceans (PISCO)
1951–present
Pacific Northwest Coastal Ecosystems Research Study (PNCERS)
ca. 1997–2001
Vancouver Island Shelf
1985–present
Line P
1949–present
Exxon Valdez Oil Spill (EVOS) Sound Ecosystem Assessment (SEA) EVOS Gulf Ecosystem Monitoring (GEM) program
1993–1998
1989–present 1998–2002
2003–? (possibly 100 years)
Coastal Ocean Processes 2001–2004 (CoOP) Coastal Ocean Advances in Shelf Transport (COAST) CoOP Wind Events and Shelf 2000–2004 Transport (WEST) Climate Variability and Predictability (CLIVAR)
1995–2010
Argo
2001–?
Investigaciones Mexicanas de 1997–present la Corriente de California (IMECOCAL)
Focus
Climate forcing of ocean physics and impacts on coastal ecosystems California Current, esp. Southern Hydrography and plankton and California Bight fish distributions and composition Monterey Bay Hydrography, plankton biogeochemistry U.S. West Coast; California Hydrography, marine Current from Oregon to Southern meroplankton distribution; larval California recruitment, and adult benthic invertebrates U.S. West Coast, esp. Willapa Research and outreach on Bay and Grays Harbor, WA, and coastal management issues Tillamook Bay and Coos Bay, OR Shelf West of Vancouver Island Hydrography, nutrients, plankton, birds Transect from Juan de Fuca Strait Hydrography, nutrients, plankton to Ocean Station Papa Prince William Sound, AK Hydrography, productivity, and trophic ecology of marine organisms Prince William Sound, Cook Inlet Hydrography, productivity, and adjacent shelf ecosystem, AK diversity, trophic ecology of zooplankton to birds and mammals Nearshore Oregon shelf Atmospheric forcing, ecosystem hydrography, productivity, cross-shelf transport No. California; Pt. Arena to San Francisco Bay
Atmospheric forcing, ocean response and trophic responses; cross-shelf transport Worldwide; esp.Pacific Basin Climate variability and Extended Climate Study (PBECS) predictability at seasonal to centennial time scales Worldwide; extensive coverage in Heat and freshwater storage and NEP transport in oceanic realm Baja California’s west coast, Climate change impacts on Southern part of the California hydrography, zooplankton, Current System ichthyoplankton and pelagic fish
focused process-oriented field research in the CCS and CGOA, respectively. The 12 papers in this issue present some results from the modeling, retrospective and long-term observations initiated in Phase I. Eight of the contributions in this issue use existing long-term data sets or proxies to examine temporal variability in the NEP ecosystem. Schwing et al. and Mendelssohn and Schwing examine large scale climatological patterns in the eastern Pacific of both the Northern and Southern Hemispheres. Two papers by Strub and James document seasonal and interannual variability, including the response of large-scale surface
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Fig. 4. Map of selected recent, ongoing, or planned ocean research programs in the Northeast Pacific.
circulation to a strong El Nin˜ o. The longest-duration biological data set for the eastern North Pacific is the 50-year record of zooplankton abundance collected by the CalCOFI program. Zooplankton volumes from that time series have been used to document the dramatic 3- to 4-fold decline in zooplankton biomass that occurred off Southern California, beginning at approximately the time of the mid 1970s warming event in the California Current System (Roemmich & McGowan, 1995). To date, there has been little investigation of zooplankton species compositional changes during this period of declining overall biomass. Rebstock and her colleagues are examining this decline, but first she addresses the question of whether a 1978 change in the zooplankton sampling gear had an effect on species-specific capture efficiency. Rebstock reports that the sampling gear change did not introduce species specific biases in sampling efficiency, suggesting that compositional changes that occur during the CalCOFI sampling period were responses to variable or changing ocean conditions. Satterfield and Finney use stable isotope analysis to examine the late 1990s trophic status of five Pacific salmon species, and use isotope analysis of sockeye scales from layered lake sediments spanning 30 years to retrospectively document shifts in trophic level, shift in foraging region, or changes in the isotopic composition at the base of the food web (e.g., a change in ocean conditions). Doyle and her co-authors document regional variations in ichthyoplankton assemblages in the Northeast Pacific Ocean, including the Bering Sea, Northern Gulf of Alaska and California Current. Botsford and Lawrence re-examine the historical records of salmon abundance in the Northeast Pacific, and find that the story is not quite as simple as “salmon populations in the CCS and CGOA covary out-of-phase”.
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Chinook salmon populations remained relatively stable in both the CCS and CGOA, whereas Coho salmon and Dungeness crab populations in the CCS declined during the 1970–80s, generally indicating an adverse response to the generally warmer ocean conditions. The results of two modeling studies are reported. Batchelder et al. use a model to explore the interaction of ontogenetically and physiologically variable diel vertical migration and nearshore cross-shelf flows. They report that nearshore retention, survival and overall population abundance were strongly controlled by the interaction of diel vertical migration and depth varying transports. Hermann et al. describe the coupling of a regional circulation model with a global circulation model, evaluate the impacts of subtidal and tidal forcing, and compare the regional model output to selected oceanographic observations. Finally, there are two papers reporting results from Long-Term Observation Program (LTOP) studies implemented by U.S. GLOBEC off Northern California and Oregon. A paper by Hill and Wheeler documents the spatial variability of organic carbon and nitrogen in different water masses in the region. Peterson and Keister compare abundance, distribution and species composition of zooplankton north and south of a prominent cape, during two years of contrasting ocean conditions. These studies form the foundation for the investigations scheduled in the next decade in the Northeast Pacific Ocean. All of the major types of investments undertaken by U.S. and international GLOBEC programs are covered. Specifically, these preliminary projects provide a first look at various aspects that will be more completely described by data collected in this and other programs in the NEP—a region that seems especially responsive to variable climate forcing.
Acknowledgements This is contribution #194 of the U.S. GLOBEC program, jointly funded by the National Science Foundation and National Oceanic and Atmospheric Administration. The writing of this paper was supported under NSF Grants OCE-0003273 and OCE-0002047. Harold P. Batchelder, College of Oceanic and Atmospheric Science, Oregon State University, 104 Ocean Admin Building, Corvallis, OR 97331-5503, USA E-mail address: [email protected] Thomas M. Powell, University of California, Department of Integrative Biology, 3060 Valley Life Sciences Building, Berkeley, CA 94720-3140, USA PII: S0079-6611(02)00026-5
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