EFFECTS OF INTERDECADAL CLIMATE VARIABILITY ON THE OCEANIC ECOSYSTEMSOF THE NE PACIFIC

A major reorganization of the North-east Pacific biota transpired foll owing a climatic 'regime shift' in the mid 1970s. In this paper, we ch aracterize the effects of interdecadal climate forcing on the oceanic ecosystems of the NE Pacific Ocean. We consider the concept of scale i n terms of both time and space within the North Pacific ecosystem and develop a conceptual model to illustrate how climate variability is li nked 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 ecosyst ems - primary and secondary producers, forage species, and several lev els of predators. They have been undertaken at different time and spac e scales. However, taken together, they reveal a more coherent picture of how decadal-scale climate forcing may affect the large oceanic eco systems of the NE Pacific. Finally, we synthesize the insight gained f rom interpreting these studies. Several general conclusions can be dra wn. 1 There are large-scale, low-frequency, and sometimes very rapid c hanges in the distribution of atmospheric pressure over the North Paci fic which are, in turn, reflected in ocean properties and circulation. 2 Oceanic ecosystems respond on similar time and space scales to vari ations 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 eco system response to climate forcing, they provide only hints of the mec hanisms of interaction. 5 A model whereby ecosystem response to specif ied climate variation can be successfully predicted will be difficult to achieve because of scale mismatches and nonlinearities in the atmos phere-ocean-biosphere system.