Climate Change and...
Effects of Climate Change
- Climate Variability
- Climate Models
Effects of Climate Change
R. C. Smith, D. Ainley, K. Baker, E. Domack, S. Emslie, B. Fraser, J. Kennett, A. Leventer, E. Mosley-Thompson, S. Stammerjohn, M. Vernet (1999). Marine ecosystem sensitivity to climate change. BioScience 49 (5): 393-404
ABSTRACT: Mounting evidence suggests that the earth is experiencing a period of rapid climate change. Never before has it been so important to understand how environmental change influences the earth’s biota and to distinguish anthropogenic change from natural variability. Long-term studies in the western Antarctic Peninsula (WAP) region provide the opportunity to observe how changes in the physical environment are related to changes in the marine ecosystem. Analyses of paleoclimate records (Mosley-Thompson 1992, Peel 1992, Domack et al. 1993, Thompson et al. 1994, Dai et al. 1995, Domack and McClennen 1996, Leventer et al. 1996) have shown that the WAP region has moved from a relatively cold regime between approximately 2700 BP and 100 BP, to a relatively warm regime during the current century. Air temperature records from the last half-century show a dramatic warming trend, confirming the rapidity of change in the WAP area (Sansom 1989, Stark 1994, Rott et al. 1996, Smith et al. 1996). Significantly, polar ecosystem research over the last few decades (Fraser et al. 1992, Trivelpiece and Fraser 1996) and paleoecological records for the past 500 years (Emslie 1995, Emslie et al. 1998) reveal ecological transitions that have occurred in response to this climate change.
In this article, we summarize the available data on climate variability and trends in the WAP region and discuss these data in the context of long-term climate variability during the last 8000 years of the Holocene. We then compare the available data on ecosystem change in the WAP region to the data on climate variability. Both historical and paleoenvironmental records indicate a climate gradient along the WAP that includes a dry, cold continental regime to the south and a wet, warm maritime regime to the north. The position of this climate gradient has shifted over time in response to the dominant climate regime, and it makes the WAP region a highly sensitive location for assessing ecological responses to climate variability. Our findings show that this century’s rapid climate warming has occurred concurrently with a shift in the population size and distribution of penguin species.
ABSTRACT: Understanding how climate change will affect the planet is a key issue worldwide. Questions concerning the pace and impacts of climate change are thus central to many ecological and biogeochemical studies, and addressing the consequences of climate change is now high on the list of priorities for funding agencies. Here, we review the interactions between climate change and plankton communities, focusing on systematic changes in plankton community structure, abundance, distribution and phenology over recent decades. We examine the potential socioeconomic impacts of these plankton changes, such as the effects of bottom-up forcing on commercially exploited fish stocks (i.e. plankton as food for fish). We also consider the crucial roles that plankton might have in dictating the future pace of climate change via feedback mechanisms responding to elevated atmospheric CO2 levels. An important message emerges from this review: ongoing plankton monitoring programmes worldwide will act as sentinels to identify future changes in marine ecosystems.
J. C. Orr, V. J. Fabry, O. Aumont, L. Bopp, S. C. Doney, R. A. Feely, A. Gnanadesikan, N. Gruber, A. Ishida, F. Joos, R. M. Key, K. Lindsay, E. Maier-Reimer, R. Matear, P. Monfray, A. Mouchet, R. G. Najjar, G. Plattner, K. B. Rodgers, C. L. Sabine, J. L. Sarmiento, R. Schlitzer, R. D. Slater, I. J. Totterdell, M. Weirig, Y. Yamanaka, A. Yool (2005). Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437 (29 September): 681-686
ABSTRACT: Today's surface ocean is saturated with respect to calcium carbonate, but increasing atmospheric carbon dioxide concentrations are reducing ocean pH and carbonate ion concentrations, and thus the level of calcium carbonate saturation. Experimental evidence suggests that if these trends continue, key marine organisms—such as corals and some plankton—will have difficulty maintaining their external calcium carbonate skeletons. Here we use 13 models of the ocean–carbon cycle to assess calcium carbonate saturation under the IS92a 'business-as-usual' scenario for future emissions of anthropogenic carbon dioxide. In our projections, Southern Ocean surface waters will begin to become undersaturated with respect to aragonite, a metastable form of calcium carbonate, by the year 2050. By 2100, this undersaturation could extend throughout the entire Southern Ocean and into the subarctic Pacific Ocean. When live pteropods were exposed to our predicted level of undersaturation during a two-day shipboard experiment, their aragonite shells showed notable dissolution. Our findings indicate that conditions detrimental to high-latitude ecosystems could develop within decades, not centuries as suggested previously.
ABSTRACT: This paper presents a discussion of the status of the field of coral geochemistry as it relates to the recovery of past records of ocean chemistry, ocean circulation, and climate. The first part is a brief review of coral biology, density banding, and other important factors involved in understanding corals as proxies of environmental variables. The second part is a synthesis of the information available to date on extracting records of the carbon cycle and climate change. It is clear from these proxy records that decade time-scale variability of mixing processes in the oceans is a dominant signal. That Western and Eastern tropical Pacific El Niño-Southern Oscillation (ENSO) records differ is an important piece of the puzzle for understanding regional and global climate change. Input of anthropogenic CO2 to the oceans as observed by13 C and14 C isotopes in corals is partially obscured by natural variability. Nonetheless, the general trend over time toward lowerd18O values at numerous sites in the world’s tropical oceans suggests a gradual warming and/or freshening of the surface ocean over the past century.
ABSTRACT: General circulation models predict that freshwater discharge from the Mississippi River (USA) to the coastal ocean would increase 20% if atmospheric CO2 concentration doubles. Here we use a coupled physical-biological 2-box model to investigate the potential impacts of increased freshwater and nutrient inputs on the production and decay of organic matter in the coastal waters of the northern Gulf of Mexico. Model results for a doubled CO2 climate indicate that the annual net productivity of the upper water column (NP, 0 to 10 m) is likely to increase by 65 g C m-2 yr-1 , relative to a 1985-1992 average (122 g C m-2 yr-1 ). Interestingly, this projected increase is of the same magnitude as the one that has occurred slnce the 1940s due to the introduction of anthropogenlc nutrients. An increase in annual NP of 32 g C m-2 yr-1 was observed during the Great Mississippi River Flood of 1993, thus indicating the general validity of a doubled CO2 scenario. The total oxygen uptake in the lower water column (10 to 20 m), in contrast, is likely to remain at its present value of about 200 g O2 m-2 yr-1 . Thus, carbon export and burial, rather than in situ respiration, are likely to be the dominant processes balancing coastal carbon budgets, leading perhaps to an expanded extent of the hypoxic zone.
ABSTRACT: Sea temperatures in many tropical regions have increased by almost 1°C over the past 100 years, and are currently increasing at ~1–2°C per century. Coral bleaching occurs when the thermal tolerance of corals and their photosynthetic symbionts (zooxanthellae) is exceeded. Mass coral bleaching has occurred in association with episodes of elevated sea temperatures over the past 20 years and involves the loss of the zooxanthellae following chronic photoinhibition. Mass bleaching has resulted in significant losses of live coral in many parts of the world. This paper considers the biochemical, physiological and ecological perspectives of coral bleaching. It also uses the outputs of four runs from three models of global climate change which simulate changes in sea temperature and hence how the frequency and intensity of bleaching events will change over the next 100 years. The results suggest that the thermal tolerances of reef-building corals are likely to be exceeded every year within the next few decades. Events as severe as the 1998 event, the worst on record, are likely to become commonplace within 20 years. Most information suggests that the capacity for acclimation by corals has already been exceeded, and that adaptation will be too slow to avert a decline in the quality of the world’s reefs. The rapidity of the changes that are predicted indicates a major problem for tropical marine ecosystems and suggests that unrestrained warming cannot occur without the loss and degradation of coral reefs on a global scale.
ABSTRACT: Observations show that wind-driven upwelling along the California coast has increased over the past 30 years. Some have postulated that the increase in wind-driven upwelling is due largely to increased greenhouse gas forcing, but such an association has been speculative. Since global and regional simulations of future wind-driven upwelling do not exist for the California coast, we used a regional climate model (RCM) to estimate changes in wind-driven upwelling under increased CO2 concentrations. Here we show in both equilibrium and transient climate experiments that there is an intensified upwelling season, with some changes in seasonality of upwelling. This intensification may lead to enhanced productivity along the coast of California and possibly ameliorate increases in sea surface temperature due to greenhouse gas forcing.
ABSTRACT: Major changes in species distribution and abundance in North Pacific marine ecosystems are often correlated with climatic shifts in the twentieth century. Species affected in the past include halibut in the Gulf of Alaska, sardine near Japan, and various species along the Oregon/California coast. Because these changes can affect the fishing industry, we have investigated possible future climate patterns in the North Pacific based on the evaluation of 22 coupled atmosphere-ocean general circulation models (GCMs). These GCMs were made available to the science community for independent evaluation in preparation for the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC).
INTRODUCTION: Climatic variations and climate change may affect the abundance, availability and even the continued existence of a wide range of natural resources. Many of these resources are not owned and controlled as private property. Rather, they are common or public property resources that are managed with varying degrees of effectiveness by local, national or international public authorities. Marine fisheries, particularly those exploited by more than one nation, are notable examples of climate-sensitive resources whose management is complicated by the difficulty of defining and enforcing exclusive rights to the resource.
The Pacific salmon stocks of North America are transboundary resources in that they cross state and international boundaries in their oceanic migrations. There are five species of Pacific salmon (chinook, coho, sockeye, pink and chum), with a multitude of distinct breeding populations. While the various species, and even different stocks of the same species, follow somewhat different life histories, all Pacific salmon are anadromous. In other words, they spawn in freshwater streams. The juveniles migrate to the ocean where they often traverse enormous distances as they feed and mature. Mature salmon then return to their natal streams to spawn and die. Their anadromous nature makes salmon sensitive to changes both in the ocean and stream environments. It also creates a perplexing set of difficulties for effective management.
The United States and Canada have a long and rocky history of alternating between cooperating on joint management of Pacific salmon harvests and squabbling over their respective shares of the catch. The most recent breakdown in cooperation began in 1993, when the two nations became embroiled in an extended dispute that left them unable to agree on a full set of salmon "fishing regimes" under the terms of the Pacific Salmon Treaty. A new Agreement, signed on June 30, 1999, may end the conflict, but it is too early to judge its likelihood of success. The Canadians remain bitterly divided over the merits of the Agreement, which has been labeled a "sellout" by Canadian fishing interests, and the arrangement is still contingent on U.S. Congressional approval of $140 million for two jointly managed endowment funds to be used for scientific cooperation, stock enhancement and habitat restoration (Culbert and Beatty, 1999). The Agreement is also contingent on a U.S. Federal Government determination, by December 31,1999, that the Agreement satisfies the legal requirements of the Endangered Species Act (U.S. Department of State, 1999).
The recent acrimony began when northern salmon runs increased dramatically while southern runs declined, leading to a change in the overall balance of "interceptions " between the U.S. and Canada. These trends appear to be influenced by the effects of climatic variations on the ocean and stream environments, but climate is not the only source of harvest variability. Because it is difficult to disentangle natural and anthropogenic sources of variability, the negotiation process has been complicated by differences of opinion over the biological "facts". When marine survival rates for chinook and coho salmon originating in Washington, Oregon and British Columbia declined sharply during the early 1990s, the Parties proved unable to quickly and effectively constrain harvests (PSC-JCTC, 1994; PSC, 1995; 1996; Confederated Tribes and Bands v. Baldridge [W.D. Wash. September 7, 1995]). This almost certainly contributed to the current imperiled state of some of these stocks, culminating in recent listings of some Columbia Basin and Puget Sound chinook stocks under the Endangered Species Act (Shaffer, 1998; Whitman, 1999).
The complex role of an extended climatic regime-shift (Hare and Francis, 1995; Mantua et al., 1997) in this dispute suggests that future efforts to adapt to greenhouse gas-induced climate change may encounter analogous pitfalls. A better understanding of the role of unanticipated climatic trends or shifts in current resource-management disputes may help to smooth the path of adaptation, for example, by encouraging the development of more flexible allocation rules. Accordingly, this paper has two goals. The first is to summarize the nature of the possible impacts of anthropogenic climate change on Pacific salmon. The second is to draw lessons from the Treaty dispute regarding the process of adaptation in the case of transboundary fishery resources.
P. W. Mote, E. A. Parson, A. F. Hamlet, W. S. Keeton, D. Lettenmaier, N. Mantua, E. L. Miles, D. W. Peterson, D. L. Peterson, R. Slaughter, A. K. Snover (2003). Preparing for climatic change: the water, salmon, and forests of the Pacific Northwest. Climatic Change 61 (1-2): 45-88
ABSTRACT: The impacts of year-to-year and decade-to-decade climatic variations on some of the Pacific Northwest's key natural resources can be quantified to estimate sensitivity to regional climatic changes expected as part of anthropogenic global climatic change. Warmer, drier years, often associated with El Niño events and/or the warm phase of the Pacific Decadal Oscillation, tend to be associated with below-average snowpack, streamflow, and flood risk, below-average salmon survival, below-average forest growth, and above-average risk of forest fire. During the 20th century, the region experienced a warming of 0.8 °C. Using output from eight climate models, we project a further warming of 0.5–2.5 °C (central estimate 1.5 °C) by the 2020s, 1.5–3.2 °C (2.3 °C) by the 2040s, and an increase in precipitation except in summer. The foremost impact of a warming climate will be the reduction of regional snowpack, which presently supplies water for ecosystems and human uses during the dry summers. Our understanding of past climate also illustrates the responses of human management systems to climatic stresses, and suggests that a warming of the rate projected would pose significant challenges to the management of natural resources. Resource managers and planners currently have few plans for adapting to or mitigating the ecological and economic effects of climatic change.
ABSTRACT: Retrospective analyses of Pacific Basin climate records highlight the existence of a pan-Pacific interdecadal climate oscillation. We find strong evidence for coherent patterns of interdecadal variability in Pacific winds, sea level pressures, and upper ocean temperatures. Collectively, the ocean-atmosphere pattern of variability has been labeled the “Pacific Decadal Oscillation”, or PDO. An index for the PDO has been developed from an empirical orthogonal function (EOF) analysis of north Pacific SST records dating back to 1900.
An analysis of Pacific coast salmon catch records suggests that the dominant pattern of salmon production is driven by low-frequency climate variations associated with the PDO. The characteristics of this salmon production pattern of variability include a preferentially interdecadal time scale of variation that is coherent with our PDO index, and a north-south inverse production pattern in which Alaska stocks tend to be productive while those in the Pacific northwest are relatively unproductive (and vice versa).
Mantua, N.J., S.R. Hare, Y. Zhang, J.M. Wallace, R.C. Francis (1997). A Pacific decadal climate oscillation with impacts on salmon production. Bulletin of the American Meteorological Society 78 (6): 1069-1079
ABSTRACT: Evidence gleaned from the instrumental record of climate data identifies a robust, recurring pattern of ocean-atmosphere climate variability centered over the mid-latitude Pacific basin. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal time scales. There is evidence of reversals in the prevailing polarity of the oscillation occurring around 1925, 1947, and 1977; the last two reversals correspond with dramatic shifts in salmon production regimes in the North Pacific Ocean. This climate pattern also affects coastal sea and continental surface air temperatures, as well as streamflow in major west coast river systems, from Alaska to California.
ABSTRACT: This paper explores the effects of the interaction of anthropogenic trends and climate cycles on salmon declines in the Columbia and Snake river basins. A basic population model, including anthropogenic and environmental factors, is discussed and literature relating decadal scale climate patterns and the response of the North Pacific ecosystem is reviewed. From this background a ratchet-like decline in Columbia and Snake river salmon production resulted from the interactions of human activities and climatic regime shifts. These interactions are illustrated using hundred year patterns in spring chinook salmon (Oncorhynchus tshawytscha ) catch, the Columbia River hydroelectric generating capacity, and a climate index characterizing the shifts between a cool/wet regime favorable to West Coast salmon and a warm/dry regime unfavorable to West Coast salmon. A half century correlation of the climate index and chinook catch suggest that a favorable climate regime counteracted detrimental impacts of hydrosystem development between 1945 and 1977, while an unfavorable climate regime negated beneficial effects of salmon mitigation efforts after 1977. This hypothesis is elaborated by a comparison of changes in the climate index relative to changes in Snake River salmon survival indicators.
Proposed Snake River salmon restoration plans are considered in terms of this counteractive effects hypothesis. The recent declines of salmon stocks have led a number of groups to propose plans that discontinue the present recovery actions, especially transportation of juveniles salmon around the dams. This paper hypothesizes that salmon recovery efforts, in part, have been limited by recent poor climate/ocean conditions. If this hypothesis is true, then eliminating the transportation program could be detrimental to fish. If the hypothesis is false, then eliminating transportation may be a viable recovery measure. In either case resolving the issue of counteracting processes is essential prior to making major changes to the hydrosystem operations.
ABSTRACT: Changes in oceanic primary production, linked to changes in the network of global biogeochemical cycles, have profoundly influenced the geochemistry of Earth for over 3 billion years. In the contemporary ocean, photosynthetic carbon fixation by marine phytoplankton leads to formation of ~45 gigatons of organic carbon per annum, of which 16 gigatons are exported to the ocean interior. Changes in the magnitude of total and export production can strongly influence atmospheric CO2 levels (and hence climate) on geological time scales, as well as set upper bounds for sustainable fisheries harvest. The two fluxes are critically dependent on geophysical processes that determine mixed-layer depth, nutrient fluxes to and within the ocean, and food-web structure. Because the average turnover time of phytoplankton carbon in the ocean is on the order of a week or less, total and export production are extremely sensitive to external forcing and consequently are seldom in steady state. Elucidating the biogeochemical controls and feedbacks on primary production is essential to understanding how oceanic biota responded to and affected natural climatic variability in the geological past, and will respond to anthropogenically influenced changes in coming decades. One of the most crucial feedbacks results from changes in radiative forcing on the hydrological cycle, which influences the aeolian iron flux and, in turn, affects nitrogen fixation and primary production in the oceans.
ABSTRACT: Historical catch records suggest that climatic variability has had basin-wide effects on the northern Pacific and its fish populations, such as salmon, sardines and anchovies. However, these records are too short to define the nature and frequency of patterns. We reconstructed similar to 2,200-year records of sockeye salmon abundance from sediment cores obtained from salmon nursery lakes on Kodiak Island, Alaska. Large shifts in abundance, which far exceed the decadal-scale variability recorded during the past 300 years, occurred over the past two millennia. A marked, multi-centennial decline in Alaskan sockeye salmon was apparent from ~ 100 BC to AD 800, but salmon were consistently more abundant from AD 1200 to 1900. Over the past two millennia, the abundances of Pacific sardine and Northern anchovy off the California coast, and of Alaskan salmon, show several synchronous patterns of variability. But sardines and anchovies vary out of phase with Alaskan salmon over low frequency, which differs from the pattern detected in historical records. The coherent patterns observed across large regions demonstrate the strong role of climatic forcing in regulating northeastern Pacific fish stocks.
Finney, B. P., I. Gregory-Eaves, J. Sweetman, M.S.V. Douglas, J.P. Smol (2000). Impacts of climatic change and fishing on Pacific salmon abundance over the past 300 years. Science 290 (27 October): 795-799
ABSTRACT: The effects of climate variability on Pacific salmon abundance are uncertain because historical records are short and are complicated by commercial harvesting and habitat alteration. We use lake sediment records ofd15 N and biological indicators to reconstruct sockeye salmon abundance in the Bristol Bay and Kodiak Island regions of Alaska over the past 300 years. Marked shifts in populations occurred over decades during this period, and some pronounced changes appear to be related to climatic change. Variations in salmon returns due to climate or harvesting can have strong impacts on sockeye nursery lake productivity in systems where adult salmon carcasses are important nutrient sources.
ABSTRACT: Pink (Oncorhynchus gorbuscha ), chum (O. keta ), and sockeye salmon (O. nerka ) represent approximately 90% of the commercial catch of Pacific salmon taken each year by Canada, Japan, the United States, and Russia. Annual all-nation catches of the three species and of each species, from 1925 to 1989, exhibited long-term parallel trends. National catches, in most cases, exhibited similar but weaker trends. The strong similarity of the pattern of the all-nation pink, chum, and sockeye salmon catches suggests that common events over a vast area affect the production of salmon in the North Pacific Ocean. The climate over the northern North Pacific Ocean is dominated in the winter and spring by the Aleutian Low pressure system. The long-term pattern of the Aleutian Low pressure system corresponded to the trends in salmon catch, to copepod production, and to other climate indices, indicating that climate and the marine environment may play an important role in salmon production.
R. J. Beamish, J. T. Schnute, A. J. Cass, C. M. Neville, R. M. Sweeting (2004). The influence of climate on the stock and recruitment of pink and sockeye salmon from the Fraser River, British Columbia, Canada. Transactions of the American Fisheries Society 133 (6): 1396-1412
ABSTRACT: The relationships between the spawning stock and the subsequent recruitment of pink salmonOncorhynchus gorbuscha and sockeye salmonO. nerka from the Fraser River improve significantly when the data are separated by climate and ocean regimes. Our analyses show changes in these relationships as regimes shift, indicating that the trend in marine survival of pink and sockeye salmon changes on a decadal scale. In general, the climate and ocean regime from 1977 to 1988 was productive for pink and sockeye salmon. However, the regime in the 1990s was characterized by reduced productivity for both species. The occurrence of a natural shift in the trend of pink and sockeye salmon production on a decadal scale should be incorporated into the management of Pacific salmon stocks to ensure that annual catches, escapements, and planned stock abundances are consistent with the productivity of a particular regime.
ABSTRACT: Benthic foraminiferal assemblages from Santa Barbara Basin exhibit major faunal and ecological switches associated with late Quaternary millennial- to decadal-scale global climate oscillations. Repeated turnovers of entire faunas occurred rapidly (<40–400 yr) without extinction or speciation in conjunction with Dansgaard-Oeschger shifts in thermohaline circulation, ventilation, and climate, confirming evolutionary model predictions of Roy et al. Consistent faunal successions of dysoxic taxa during successive interstadials reflect the extreme sensitivity and adaptation of the benthic ecosystem to the rapid environmental changes that marked the late Quaternary and possibly other transitional intervals in the history of the Earth’s oceanatmosphere-cryosphere system. These data support the hypothesis that broad segments of the biosphere are well adapted to rapid climate change.
Dolloff, C.A., P.A. Flebbe, M.D. Owen (1994). Fish habitat and fish populations in a southern Appalachian watershed before and after Hurricane Hugo. Transactions of the American Fisheries Society 123 (4): 668-678
ABSTRACT: Habitat features and relative abundance of all fish species were estimated in 8.4 km of a small mountain stream system before and 11 months after Hurricane Hugo crossed the southern Appalachians in September 1989. There was no change in the total amount (area) of each habitat type but the total number of habitat units decreased and average size and depth of habitat units increased. Transport and sorting of streambed sediments was evident from the increased proportion of habitat units in which cobbles and small boulders were the most common constituents. Large woody debris more than doubled from 228 to 559 pieces/km of stream channel. At the watershed scale, there were only minor changes in the fish community 11 months after the hurricane, Eleven species were found both before and after the storm, and most species were uncommon. Among common species, densities increased in riffles for dartersEtheostoma spp., increased in pools for blacknose dace Rhinichthys atratulus, and were largely unaffected for rainbow troutOncorhynchus mykiss . The results of this case study suggest that the effects of catastrophic disturbances on fish habitat and populations depend on the predisturbance condition of instream and riparian habitat, timing of the disturbance, and life histories of individual species.
D. Justic, N. N. Rabalais, R. E. Turner (1996). Effects of climate change on hypoxia in coastal waters: a doubled CO2 scenario for the northern Gulf of Mexico. Limnology and Oceanography 41 (5): 992-1003
ABSTRACT: Projections of general circulation models suggest that freshwater discharge from the Mississippi River to the coastal ocean will increase 20% CO2 concentration doubles. This result is likely to affect water column stability, surface productivity, and global oxygen cycling in the northern Gulf of Mexico, which is the site of the largest (up to 16,500 km2 ) and most severe hypoxic zone ( < 2 mg O2 liter-1 ) in the western Atlantic Ocean. We use a coupled physical-biological two-box model to investigate potential effects of climate change on seasonal oxygen cycling and hypoxia in river-dominated coastal waters. The model was developed and calibrated using comprehensive environmental data sets collected on the Mississippi River and in the northern Gulf of Mexico between 1985 and 1993. The relative magnitude of changes in river runoff and severity of hypoxia during the 1993 Mississippi River flooding provide an excellent data set for model verification. Model simulations for a doubled CO2 climate predict a 30-60% decrease in summertime subpycnoclinal oxygen content, relative to a 1985-1992 average. Under those conditions, the hypoxic zone in the northern Gulf of Mexico will expand and encompass an area greater than that of summer 1993.
ABSTRACT: Conservation management is always a political, as well as a biological, problem. Oregon's coastal natural coho salmon (Oncorhynchus kisutch ) populations have drawn political attention because abundances are at critically low levels. One of the underlying problems is a long-term trend of habitat degradation. In addition, decadal-scale cycles in ocean survival of coho salmon may lead to cycles in abundance that are independent of freshwater habitat trends. Programs to restore coho salmon populations through stream restoration will take decades to produce long-lasting results. When population abundance varies widely over time, a rise in abundance following the initiation of recovery measures can be taken as an indication of success even when the increase in numbers was independent of the actions taken. Support for recovery efforts must be sustained through the cycle of higher abundance. The true measure of success for such projects is the continued survival of the population through subsequent episodes of low abundance.
ABSTRACT: The role of climatic variation in regulating marine populations and communities is not well understood. To improve our knowledge, the sign, amplitude, and frequency of climatic and biotic variations should be compared as a necessary first step. It is shown that there have been large interannual and interdecadal sea-surface temperature changes off the West Coast of North America during the past 80 years. Interannual anomalies appear and disappear rather suddenly and synchronously along the entire coastline. The frequency of warm events has increased since 1977. Although extensive, serial, biological observations are often incomplete, it is clear that climate-ocean variations have disturbed and changed our coastal ecosystems.
ABSTRACT: The ocean's carrying capacity for anadromous salmonids is dynamic in time and space. It is constantly changing on interannual, decadal, centennial, and millennial time scales. Since 1976 a major change has occurred in the Northeast pacific Ocean, with unfavorable ocean conditions for salmonids in the Coastal Upwelling Domain, and highly favorable conditions farther north in the Coastal Downwelling and Central Subarctic domains and the Bering Sea. High sea levels and warm temperatures along the coast, an intense Aleutian Low and weak upwelling are associated with these recent changes. During the 1960s and 1970s, when hatchery releases of smolts were increased to compensate for loss of freshwater habitat, the opposite trend prevailed, with good ocean survival in the Coastal Upwelling Domain and lower survival in the Gulf of Alaska. Although the exact mechanisms that affect high or low salmon production are still speculative, ocean climate is clearly implicated and should be considered in management decisions. Favorable ocean conditions will be required for full recovery of many depressed stocks.
INTRODUCTION: In the mid-1970s, ocean conditions in the North Pacific Ocean underwent a dramatic and abrupt change (Graham 1994). Coincident with the physical regime shift, Alaskan salmonids entered an era of greatly increased production that has persisted into the 1990s (Fig. 1). Throughout their long (over 100 yr) commercial exploitation history, several of the Alaskan salmon species have demonstrated "red noise" variability, wherein periods of high (low) production tend to persist for a lengthy period before abruptly reversing to the opposite state. For example, in the 1930s and early 1940s, salmon landings were high, followed by an era of low catches from the late 1940s to late 1970s. As Alaskan landings increased in the late 1970s, several North American west coast stocks, notably Oregon coho salmon (Oncorhynchus kisutch ; Pearcy 1992), went into a prolonged period of decline.
Much early research on variability in salmon survival (and therefore production and catch) focused on the freshwater stage of their life cycle, attempting to link survival to conditions in their spawning and rearing habitat. The period spent at sea was regarded as relatively unimportant. There is now a growing awareness of the importance of the marine environment in determining salmon production (e.g. Pearcy 1984; Beamish and McFarlane 1989).
Variability in marine survival of salmon is poorly understood (Mathews 1984). Numerous studies have attempted to correlate survival with environmental factors, though few have proven useful in predicting salmon abundance or assisting in management decision making (Pearcy 1992). Part of the difficulty in elucidating the driving factors of survival is that the relationship between the environment and survival is clouded by many factors. Biotic (e.g. intra- and inter-specific competition, prey availability, predation) and abiotic (environmental variables, habitat) factors not only exhibit complex relationships with survival (non-linear, threshold) but are themselves often highly correlated.
Despite these drawbacks, the importance of attempting to understand the causes of variable survival should not be underestimated (Francis and Sibley 1991). In particular, understanding large-scale and long-term variability would benefit both fishery managers and fishermen (Shepherd et al. 1984).
Large marine ecosystems fluctuate in response to physical forcings that occur over a number of time intervals. There appears to be a nested hierarchy of interacting processes occurring on different time scales that are relevant to their dynamics, ranging from relatively discrete processes that occur over times on the order of 1 yr or less (e.g., the 1970 North Pacific winter atmospheric circulation pattern (Hollowed and Wooster 1992)), to processes that persist over long time periods and fluctuate at the inter-century level (Baumgartner et al. 1992). What we are most interested in identifying in this analysis are regimes that define points in time, separated by intervals on the order of decades, where major jumps or shifts in the level of abundance occur in large marine ecosystems. Therefore, in examining the interannual dynamics of various biological components of large marine ecosystems, what we see are responses to these nested hierarchies of interacting processes occurring at different time scales and working synergistically to create pattern. In this analysis, it is pattern at the regime level that we are trying to interpret.
We hypothesize that regional variability in salmon production is driven by large-scale climate change, reflected in North Pacific atmospheric-oceanic regime shifts. Under this hypothesis, salmon populations exhibit two characteristics: relatively stable production while a particular regime persists, followed by a rapid transition to a new production level in response to the physical regime shift. If large-scale salmon production is closely related to North Pacific climate processes, we should find coherent shifts in mean production levels across both species and area.
In addition to the late 1970s regime shift, we surmise that an earlier shift, opposite in character, occurred in the late 1940s. Based on evidence summarized in the Discussion, we tentatively identify the regime shifts as taking place in the winters of 1946-47 and 1976-77. Our hypothesis suggests that two shifts in Alaskan salmon production should be detectable: a decrease in the late 1940s and an increase in the late 1970s.
To test this hypothesis, we proceed by statistically analyzing the historical production dynamics of four major Alaskan salmon stocks: western and central sockeye salmon (Oncorhynchus nerka ), southeast and central pink salmon (Oncorhynchus gorbuscha ). While many researchers have noted the aforementioned swings in production (e.g., Beamish and Bouillon 1994), there remained the possibility that the changes might be either random processes or nonsignificant, in a statistical sense. Owing to the high serial correlation (lack of independence between successive observations), the t-test for equality of means cannot be used to test for production shifts. We utilize a time-series technique known as intervention analysis to identify the significance, magnitude, and form of structural shifts (interventions) in the four time series. We identify and test the timing of the interventions by matching the onset of the physical regimes with the life history of the different species of salmon. Intervention analysis is a relatively recent statistical technique recommended as a method for detecting and quantifying non-random change in an unreplicated experiment (Carpenter 1990).
To test for interventions, we fitted univariate time-series models of the Box-Jenkins (1976) autoregressive integrated moving average (ARIMA) class. These ARIMA models provide a baseline fit to the correlation structure exhibited by the time series. Interventions are subsequently identified by analyzing model residuals. Model parameters are re-estimated incorporating the intervention(s), and the models compared on the basis of several criteria. After identifying the timing and nature of the interventions, we then review the evidence for synchronous large-scale physical regime shifts in the North Pacific.
Beamish, R. J., Neville, C. M., Cass, A. J. (1997). Production of Fraser River sockeye salmon (Oncorhynchus nerka ) in relation to decadal-scale changes in the climate and the ocean. Canadian Journal of Fisheries and Aquatic Sciences 54 (3): 543-554
ABSTRACT: The abundance of Fraser River sockeye salmon (Oncorhynchus nerka ) stocks was low in the 1960s, increased to high levels in the 1980s, and possibly entered a period of low abundance in recent years. The abundance changes of the combined stocks can be separated into productivity regimes that correspond to changes in climate trends. The most distinct change occurred when there was a major change in the climate over the Pacific Ocean in the winter of 1976-1977. The existence of natural shifts in abundance trends means that the high returns that occur during periods of high productivity would not be expected to occur during the low-productivity periods. The response of Fraser River sockeye to climate changes may be a specific example of a more general response by a number of species of fishes in the Pacific and perhaps in other oceans. Because the shift from one regime to the other occurred quickly in the 1970s, future shifts could also occur quickly. It is necessary to detect natural shifts in productivity when attempting to manage fishing impacts to ensure that economic expectations are sound and that overfishing does not occur.
ABSTRACT: A major reorganization of the North-east Pacific biota transpired following a climatic `regime shift' in the mid 1970s. In this paper, we characterize the effects of interdecadal climate forcing on the oceanic ecosystems of the NE Pacific Ocean. We consider the concept of scale in terms of both time and space within the North Pacific ecosystem and develop a conceptual model to illustrate how climate variability is linked to ecosystem change. Next we describe a number of recent studies relating climate to marine ecosystem dynamics in the NE Pacific Ocean. These studies have focused on most major components of marine ecosystems – primary and secondary producers, forage species, and several levels of predators. They have been undertaken at different time and space scales. However, taken together, they reveal a more coherent picture of how decadal-scale climate forcing may affect the large oceanic ecosystems of the NE Pacific. Finally, we synthesize the insight gained from interpreting these studies. Several general conclusions can be drawn.
1 There are large-scale, low-frequency, and sometimes very rapid changes in the distribution of atmospheric pressure over the North Pacific which are, in turn, reflected in ocean properties and circulation.
2 Oceanic ecosystems respond on similar time and space scales to variations in physical conditions.
3 Linkages between the atmosphere/ocean physics and biological responses are often different across time and space scales.
4 While the cases presented here demonstrate oceanic ecosystem response to climate forcing, they provide only hints of the mechanisms of interaction.
5 A model whereby ecosystem response to specified climate variation can be successfully predicted will be difficult to achieve because of scale mismatches and nonlinearities in the atmosphere–ocean–biosphere system.
ABSTRACT: Principal component analysis reveals that Pacific salmon catches in Alaska have varied inversely with catches from the U.S. West Coast during the past 70 years. If variations in catch reflect variations in salmon production, then results of our analysis suggest that the spatial and temporal characteristics of this “inverse” catch/production pattern are related to climate forcing associated with the Pacific Decadal Oscillation, a recurring pattern of pan-Pacific atmosphere-ocean variability. Temporally, both the physical and biological variability are best characterized as alternating 20-to 30-year-long regimes punctuated by abrupt reversals. From 1977 to the early 1990s, ocean conditions have generally favored Alaska stocks and disfavored West Coast stocks. Unfavorable ocean conditions are likely confounding recent management efforts focused on increasing West Coast Pacific salmon production. Recovery of at-risk (threatened and endangered) stocks may await the next reversal of the Pacific Decadal Oscillation. Managers should continue to limit harvests, improve hatchery practices, and restore freshwater and estuarine habitats to protect these populations during periods of poor ocean productivity.
J.D. Ortiz, S.B. O'Connell, J. DelViscio, W. Dean, J.D. Carriquiry, T. Marchitto, Y. Zheng, van Geen, A. (2004). Enhanced marine productivity off western North America during warm climate intervals of the past 52 k.y.. Geology 32 (6): 521-524
ABSTRACT: Studies of the Santa Barbara Basin off the coast of California have linked changes in its bottom-water oxygen content to millennial-scale climate changes as recorded by the oxygen isotope composition of Greenland ice. Through the use of detailed records from a sediment core collected off the Magdalena Margin of Baja California, Mexico, we demonstrate that this teleconnection predominantly arose from changes in marine productivity, rather than changes in ventilation of the North Pacific, as was originally proposed. One possible interpretation is that the modern balance of El Niño–La Niña conditions that favors a shallow nutricline and high productivity today and during warm climate intervals of the past 52 k.y. was altered toward more frequent, deep nutricline, low productivity, El Niño–like conditions during cool climate intervals.
EXECUTIVE SUMMARY: Over the past one hundred and fifty years, the landscape and ecosystems of the Pacific Northwest coastal region, already subject to many variable natural forces, have been profoundly affected by human activities. In virtually every coastal watershed from the Strait of Juan de Fuca to Cape Mendocino, settlement, exploitation and development of resources have altered natural ecosystems. Vast, complex forests that once covered the region have been largely replaced by tree plantations or converted to non-forest conditions. Narrow coastal valleys, once filled with wetlands and braided streams that tempered storm runoff and provided salmon habitat, were drained, filled, or have otherwise been altered to create land for agriculture and other uses. Tideflats and saltmarshes in both large and small estuaries were filled for industrial, commercial, and other urban uses. Many estuaries, including that of the Columbia River, have been channeled, deepened, and jettied to provide for safe, reliable navigation. The prodigious rainfall in the region, once buffered by dense vegetation and complex river and stream habitat, now surges down simplified stream channels laden with increased burdens of sediment and debris. Although these and many other changes have occurred incrementally over time and in widely separated areas, their sum can now be seen to have significantly affected the natural productivity of the region and, as a consequence, changed the economic structure of its human communities.
This activity has taken place in a region already shaped by many interacting and dynamic natural forces. Large-scale ocean circulation patterns, which vary over long time periods, determine the strength and location of currents along the coast, and thus affect conditions in the nearshore ocean and estuaries throughout the region. Periodic seasonal differences in the weather and ocean act on shorter time scales; winters are typically wet with storms from the southwest while summers tend to be dry with winds from the northwest. Some phenomena are episodic, such as El Niño events, which alter weather, marine habitats, and the distribution and survival of marine organisms. Other oceanic and atmospheric changes operate more slowly; over time scales of decades, centuries, and longer. Episodic geologic events also punctuate the region, such as volcanic eruptions that discharge widespread blankets of ash, frequent minor earthquakes, and major subduction zone earthquakes each 300 to 500 years that release accumulated tectonic strain, dropping stretches of ocean shoreline, inundating estuaries and coastal valleys, and triggering landslides that reshape stream profiles. While these many natural processes have altered, sometimes dramatically, the Pacific Northwest coastal region, these same processes have formed productive marine and coastal ecosystems, and many of the species in these systems have adapted to the variable environmental conditions of the region to ensure their long-term survival. The combination of these many natural processes has resulted in highly productive marine and coastal ecosystems that are adapted to the widely variable conditions of the region.
The economy and culture of the Pacific Northwest coastal region continue to depend to a large degree upon natural resources. As the landscape and coastal resources continue to be developed and, in some cases, depleted, the economic and social systems that depend on a stable, predictable set of environmental conditions to provide goods and services are increasingly vulnerable to environmental change, whether natural, human-caused, or both. Changes in environmental conditions and consequent disruptions of ecosystem functions trigger reactions in political, social, and economic systems that can consume immense amounts of social, political, and economic capital. The decline of coastal salmon stocks, for instance, has resulted in a significant effort by the Oregon and Washington state governors and agencies, Federal agencies, and local communities to find "the cause", and "restore" these stocks in coastal streams. Developing and carrying out resource management programs that are ecosystem-sensitive and have public support requires that scientists and managers work together to significantly improve understanding of the function and variability of coastal ecosystems, the effects of management practices, and the economic and social, as well as ecological, consequences of change.
Bradford, M.J., J. R. Irvine (2000). Land use, fishing, climate change, and the decline of Thompson River, British Columbia, coho salmon. Canadian Journal of Fisheries and Aquatic Sciences 57 (1): 13-16
ABSTRACT: We investigated a recent, major decline in the abundance of a large aggregate of coho salmon (Oncorhynchus kisutch ) spawning in the Thompson River, British Columbia, watershed. We found that the decline could be attributed to a declining trend in productivity likely related to changing ocean conditions, overfishing, and freshwater habitat alteration. Among individual watersheds, rates of decline in adult coho salmon abundance were correlated with agricultural land use, road density, and a qualitative measure of stream habitat status but not with the proportion of land recently logged. The recovery of these populations will require the prudent regulation of fishing, the restoration of salmon producing watersheds, and an improvement in ocean conditions.
Hunt, G.L., Jr., P. Stabeno, G. Walters, E. Sinclair, R. D. Brodeur, J. M. Napp, N. A. Bond (2002). Climate change and control of the southeastern Bering Sea pelagic ecosystem. Deep Sea Research Part II: Topical Studies in Oceanography 49 (26): 5821-5853
ABSTRACT: We propose a new hypothesis, the Oscillating Control Hypothesis (OCH), which predicts that pelagic ecosystem function in the southeastern Bering Sea will alternate between primarily bottom-up control in cold regimes and primarily top-down control in warm regimes. The timing of spring primary production is determined predominately by the timing of ice retreat. Late ice retreat (late March or later) leads to an early, ice-associated bloom in cold water (e.g., 1995, 1997, 1999), whereas no ice, or early ice retreat before mid-March, leads to an open-water bloom in May or June in warm water (e.g., 1996, 1998, 2000). Zooplankton populations are not closely coupled to the spring bloom, but are sensitive to water temperature. In years when the spring bloom occurs in cold water, low temperatures limit the production of zooplankton, the survival of larval/juvenile fish, and their recruitment into the populations of species of large piscivorous fish, such as walleye pollock (Theragra chalcogramma ), Pacific cod (Gadus macrocephalus ) and arrowtooth flounder (Atheresthes stomias ). When continued over decadal scales, this will lead to bottom-up limitation and a decreased biomass of piscivorous fish. Alternatively, in periods when the bloom occurs in warm water, zooplankton populations should grow rapidly, providing plentiful prey for larval and juvenile fish. Abundant zooplankton will support strong recruitment of fish and will lead to abundant predatory fish that control forage fish, including, in the case of pollock, their own juveniles. Piscivorous marine birds and pinnipeds may achieve higher production of young and survival in cold regimes, when there is less competition from large piscivorous fish for cold-water forage fish such as capelin (Mallotus villosus ). Piscivorous seabirds and pinnipeds also may be expected to have high productivity in periods of transition from cold regimes to warm regimes, when young of large predatory species of fish are numerous enough to provide forage. The OCH predicts that the ability of large predatory fish populations to sustain fishing pressure will vary between warm and cold regimes.
The OCH points to the importance of the timing of ice retreat and water temperatures during the spring bloom for the productivity of zooplankton, and the degree and direction of coupling between zooplankton and forage fish. Forage fish (e.g., juvenile pollock, capelin, Pacific herring [Clupea pallasii ]) are key prey for adult pollock and other apex predators. In the southeastern Bering Sea, important changes in the biota since the mid-1970s include a marked increase in the biomass of large piscivorous fish and a concurrent decline in the biomass of forage fish, including age-1 walleye pollock, particularly over the southern portion of the shelf. Populations of northern fur seals (Callorhinus ursinus ) and seabirds such as kittiwakes (Rissa spp.) at the Pribilof Islands have declined, most probably in response to a diminished prey base. The available evidence suggests that these changes are unlikely the result of a decrease in total annual new primary production, though the possibility of reduced post-bloom production during summer remains. An ecosystem approach to management of the Bering Sea and its fisheries is of great importance if all of the ecosystem components valued by society are to thrive. Cognizance of how climate regimes may alter relationships within this ecosystem will facilitate reaching that goal.