Evidence gleaned from the instrumental record of climate data identifies a robust, recurring pattern of ocean–atmosphere climate variability centered over the midlatitude North Pacific basin. Over the past century, the amplitude of this climate pattern has varied irregularly at interannual-to-interdecadal timescales. There is evidence of reversals in the prevailing polarity of the oscillation occurring around 1925, 1947, and 1977; the last two reversals correspond to 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.

/pdf/a-pacific-interdecadal-climate-oscillation-with-impacts-on-4w6o1eb1un.pdf

A Pacific interdecadal climate oscillation with impacts on salmon production

All ecosystems are exposed to gradual changes in climate, nutrient loading, habitat fragmentation or biotic exploitation. Nature is usually assumed to respond to gradual change in a smooth way. However, studies on lakes, coral reefs, oceans, forests and arid lands have shown that smooth change can be interrupted by sudden drastic switches to a contrasting state. Although diverse events can trigger such shifts, recent studies show that a loss of resilience usually paves the way for a switch to an alternative state. This suggests that strategies for sustainable management of such ecosystems should focus on maintaining resilience.

/pdf/catastrophic-shifts-in-ecosystems-2yv2mwzdwb.pdf

Catastrophic shifts in ecosystems.

Ecological extinction caused by overfishing precedes all other pervasive human disturbance to coastal ecosystems, including pollution, degradation of water quality, and anthropogenic climate change. Historical abundances of large consumer species were fantastically large in comparison with recent observations. Paleoecological, archaeological, and historical data show that time lags of decades to centuries occurred between the onset of overfishing and consequent changes in ecological communities, because unfished species of similar trophic level assumed the ecological roles of overfished species until they too were overfished or died of epidemic diseases related to overcrowding. Retrospective data not only help to clarify underlying causes and rates of ecological change, but they also demonstrate achievable goals for restoration and management of coastal ecosystems that could not even be contemplated based on the limited perspective of recent observations alone.

/pdf/historical-overfishing-and-the-recent-collapse-of-coastal-28k1p5mqjm.pdf

Historical overfishing and the recent collapse of coastal ecosystems.

A review of drought concepts

Fisheries have rarely been 'sustainable'. Rather, fishing has induced serial depletions, long masked by improved technology, geographic expansion and exploitation of previously spurned species lower in the food web. With global catches declining since the late 1980s, continuation of present trends will lead to supply shortfall, for which aquaculture cannot be expected to compensate, and may well exacerbate. Reducing fishing capacity to appropriate levels will require strong reductions of subsidies. Zoning the oceans into unfished marine reserves and areas with limited levels of fishing effort would allow sustainable fisheries, based on resources embedded in functional, diverse ecosystems.

/pdf/towards-sustainability-in-world-fisheries-26u29h5wj5.pdf

Towards sustainability in world fisheries

The Pacific Decadal Oscillation (PDO) has been described by some as a long-lived El Nino-like pattern of Pacific climate variability, and by others as a blend of two sometimes independent modes having distinct spatial and temporal characteristics of North Pacific sea surface temperature (SST) variability. A growing body of evidence highlights a strong tendency for PDO impacts in the Southern Hemisphere, with important surface climate anomalies over the mid-latitude South Pacific Ocean, Australia and South America. Several independent studies find evidence for just two full PDO cycles in the past century: “cool” PDO regimes prevailed from 1890–1924 and again from 1947–1976, while “warm” PDO regimes dominated from 1925–1946 and from 1977 through (at least) the mid-1990's. Interdecadal changes in Pacific climate have widespread impacts on natural systems, including water resources in the Americas and many marine fisheries in the North Pacific. Tree-ring and Pacific coral based climate reconstructions suggest that PDO variations—at a range of varying time scales—can be traced back to at least 1600, although there are important differences between different proxy reconstructions. While 20th Century PDO fluctuations were most energetic in two general periodicities—one from 15-to-25 years, and the other from 50-to-70 years—the mechanisms causing PDO variability remain unclear. To date, there is little in the way of observational evidence to support a mid-latitude coupled air-sea interaction for PDO, though there are several well-understood mechanisms that promote multi-year persistence in North Pacific upper ocean temperature anomalies.

https://link.springer.com/content/pdf/10.1023%2FA%3A1015820616384.pdf

The Pacific Decadal Oscillation

Empirical evidence for North Pacific regime shifts in 1977 and 1989

There are two fundamental ways of doing science: the experimental-predictive and the historical-descriptive. The experimental-predictive approach uses the techniques of controlled experiment, the reduction of natural complexity to a minimal set of general causes, and presupposes that all times can be treated alike and adequately simulated in the laboratory. The historical-descriptive approach uses a mode of analysis which is rooted in the comparative and observational richness of our data, is holistic in its treatment of systems and events, and assumes that the final result being studied is unique, i.e. dependent or contingent upon everything that came before. We suggest that one of the real difficulties we have in understanding ecosystem properties is our inability to deal with scale, and we show how historical science allows us to approach the issue of scale through the interpretation of pattern in time and space. We then use the techniques of the historical-descriptive approach to doing science in the context of our own and other research on climate change and biological production in the North-east Pacific Ocean. In particular, we examine rapid decadal-scale shifts in the abundance and distribution of two major components–salmon and zooplankton - of the large marine ecosystem of the North-east Pacific, and how they relate to similar shifts in North Pacific atmosphere and ocean climate. We conclude that they are all related, and that climate-driven regime shifts, such as those we have identified in the North-east Pacific, can cause major reorganizations of ecological relationships over vast oceanic regions.

Decadal-scale regime shifts in the large marine ecosystems of the North-east Pacific: a case for historical science

A major reorganization of the North-east Paciﬁc biotatranspired following a climatic ‘regime shift’ in the mid1970s. In this paper, we characterize the effects ofinterdecadal climate forcing on the oceanic ecosys-tems of the NE Paciﬁc Ocean. We consider the con-cept of scale in terms of both time and space withinthe North Paciﬁc ecosystem and develop a conceptualmodel to illustrate how climate variability is linked toecosystem change. Next we describe a number of re-cent studies relating climate to marine ecosystem dy-namics in the NE Paciﬁc Ocean. These studies havefocused on most major components of marine ecosys-tems – primary and secondary producers, forage spe-cies, and several levels of predators. They have beenundertaken at different time and space scales. How-ever, taken together, they reveal a more coherentpicture of how decadal-scale climate forcing may affectthe large oceanic ecosystems of the NE Paciﬁc. Finally,we synthesize the insight gained from interpretingthese studies. Several general conclusions can bedrawn.1 There are large-scale, low-frequency, and some-times very rapid changes in the distribution of atmo-spheric pressure over the North Paciﬁc which are, inturn, reﬂected in ocean properties and circulation.2 Oceanic ecosystems respond on similar time andspace scales to variations in physical conditions.3 Linkages between the atmosphere/ocean physicsand biological responses are often different across timeand space scales.4 While the cases presented here demonstrateoceanic ecosystem response to climate forcing, theyprovide only hints of the mechanisms of interaction.5 A model whereby ecosystem response to speciﬁedclimate variation can be successfully predicted will bedifﬁcult to achieve because of scale mismatches andnonlinearities in the atmosphere–ocean–biospheresystem.INTRODUCTIONIn this paper, we characterize the effects of interde-cadal climate forcing on the oceanic ecosystems of theNE Paciﬁc Ocean. Our approach is ﬁrst to reﬂect on anumber of recent studies relating climate to marineecosystem dynamics. These studies have focused onmost major components of marine ecosystems – pri-mary and secondary producers; primary, secondary andtop-level predators. They have been undertaken atdifferent time and space scales. However, taken to-gether they begin to reveal a more coherent picture ofhow decadal-scale climate forcing may affect the largeoceanic ecosystems of the NE Paciﬁc. We then syn-thesize the insight gained from these studies with whatwe know about atmospheric and oceanic physics andhow they affect these marine ecosystems.Of particular importance to this paper is the con-cept of scale. Ricklefs (1990) deﬁnes scale as thecharacteristic distance or time associated with varia-tion in natural systems. He goes on to make threeimportant points about why the concept of scale is soimportant to developing an understanding of ecosys-tem structure and dynamics.Every process and pattern has a temporal andspatial extent.

Steven R. Hare

Papers

A Pacific interdecadal climate oscillation with impacts on salmon production

The Pacific Decadal Oscillation

Empirical evidence for North Pacific regime shifts in 1977 and 1989

Decadal-scale regime shifts in the large marine ecosystems of the North-east Pacific: a case for historical science

Effects of interdecadal climate variability on the oceanic ecosystems of the NE Pacific