Publication of “Mid-latitude Wind Stress: The Energy Source For Climatic Shifts in the North Pacific Ocean” by R.H. Parrish, F.B. Schwing and R. Mendelssohn in Fishery Oceanography.
Current Status of Accomplishment or Milestone: The paper was first visualized in 1994; however, the complex computer analyses were not possible until considerable oceanographic and meterological data sets had been developed at PFEL. The paper was published in Fisheries Oceanography Vol. 9(3), 224-238, 2000.
Background: Researchers have demonstrated regime scale variability in small pelagic fishes in several major current systems and this scale of variability has been shown, in paleo-sediment analyses, to exist thousands of years before to the development of modern fisheries. More recent work has shown that many West Coast fisheries had major alterations in productivity associated with what is now known as the 1976 regime shift.
Purpose of Activity/Goal of Project: Extracts of meterological and sea surface temperature prepared for a 1994 meeting of the Regime Group suggested that large oceanographic data sets could be used to describe the physical setting of known regimes in the productivity of sardines and anchovies in several major current systems. This work was designed to describe this setting.
Description of Accomplishment and Significant Results: Analyses of atmospheric observations in the North Pacific demonstrated extensive decadal-scale variations in the mid latitude winter surface winter stress. In the decade after 1976 winter, eastward wind stress doubled over a broad area in the central North Pacific and the winter zero wind stress curl line was displaced about 6 degrees southward. This resulted in increased southward Ekman transport, increased oceanic upwelling, and increased turbulent mixing as well as a southward expansion of the area of surface divergence. All of these factors contributed to a decadal winter cold anomaly along the subtropical side of the North Pacific Current. The increased gradient in wind stress curl and southward displacement of the zero curl line also resulted in an increase in total North Pacific Current transport that occurred primarily on the equator side of this Current. Thus, surface water entering the California Current of more suptropical origin in the post-1976 decade. Time series of southward (upwelling favorable) wind stress and SST in the area off of San Francisco exhibit at least three different types of decadal departures from mean conditions. In the Gulf of Alaska altered wind direction resulted in an increased advection of productive water into the nearshore regions of the Alaska Current.
Significance of Accomplishment (e.g., to the Center, to Management, and to NMFS Strategic plan Goals): The study provides a physical description of the oceanographic regime shifts that are now known to control the fishery productivity in the Oyashio, California and Alaska Currents. The results of the study suggests that long-term yields of the major North Pacific Fisheries will vary on decadal time scales and that the system is more complex than the simple alteration between two regimes as has been proposed by other researchers.
Problems: None
Key Contact: Richard Parrish (831-648-9033; rparrish@noaa.gov).