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

ABSTRACTA 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.