163 Journal of Oceanography, Vol. 60, pp. 163 to 188, 2004 Keywords: ⋅ Pacific Ocean, ⋅ decadal variability, ⋅ ecosystems, ⋅ climate forcing, ⋅ feedbacks. * Corresponding author. E-mail: ajmiller@ucsd.edu † We consider climate variations with timescales longer than interannual (ENSO) and shorter than centennial (greenhouse- gas forcing) to have “decadal” timescales. Copyright © The Oceanographic Society of Japan. Decadal-Scale Climate and Ecosystem Interactions in the North Pacific Ocean ARTHUR J. MILLER 1 *, FEI CHAI 2 , SANAE CHIBA 3 , JOHN R. MOISAN 4 and DOUGLAS J. NEILSON 1 1 Scripps Institution of Oceanography, La Jolla, CA 92093-0224, U.S.A. 2 School of Marine Sciences, University of Maine, Orono, ME 04469-5741, U.S.A. 3 Frontier Research System for Global Change, Japan Marine Science & Technology Center, Yokohama 236-0001, Japan 4 NASA/GSFC Wallops Flight Facility, Wallops Island, VA 23337-5099, U.S.A. (Received 25 August 2003; in revised form 31 October 2003; accepted 6 November 2003) Decadal-scale climate variations in the Pacific Ocean wield a strong influence on the oceanic ecosystem. Two dominant patterns of large-scale SST variability and one domi- nant pattern of large-scale thermocline variability can be explained as a forced oce- anic response to large-scale changes in the Aleutian Low. The physical mechanisms that generate this decadal variability are still unclear, but stochastic atmospheric forc- ing of the ocean combined with atmospheric teleconnections from the tropics to the midlatitudes and some weak ocean-atmosphere feedbacks processes are the most plau- sible explanation. These observed physical variations organize the oceanic ecosystem response through large-scale basin-wide forcings that exert distinct local influences through many different processes. The regional ecosystem impacts of these local proc- esses are discussed for the Tropical Pacific, the Central North Pacific, the Kuroshio- Oyashio Extension, the Bering Sea, the Gulf of Alaska, and the California Current System regions in the context of the observed decadal climate variability. The physi- cal ocean-atmosphere system and the oceanic ecosystem interact through many dif- ferent processes. These include physical forcing of the ecosystem by changes in solar fluxes, ocean temperature, horizontal current advection, vertical mixing and upwelling, freshwater fluxes, and sea ice. These also include oceanic ecosystem forcing of the climate by attenuation of solar energy by phytoplankton absorption and atmospheric aerosol production by phytoplankton DMS fluxes. A more complete understanding of the complicated feedback processes controlling decadal variability, ocean ecosystems, and biogeochemical cycling requires a concerted and organized long-term observa- tional and modeling effort. timescales increasingly reveal distinct linkages between the physical ocean climate and the oceanic ecosystem. It is imperative to develop a clear understanding of the mechanisms that lead to these physical-biological changes because of the important economical and societal impacts that these variations wield on our global communities. Our objective here is to summarize key aspects of the current state of understanding of the processes con- trolling physical climate decadal variations of the Pacific Ocean, the oceanic ecosystem changes that have been observed to occur in the Pacific with similar timescales, and the mechanisms by which the physical environmen- tal changes may alter the oceanic ecosystem and vice versa. 1. Introduction As observations of the Pacific Ocean physical-bio- logical system accumulate through extensive networks of observing systems, prominent fluctuations on decadal †