Complete Study on Seasonal Variation in the Aleutian Low
and North Pacific High Pressure Systems
Current Status of Accomplishment or Milestone: The study has been completed, with the results summarized in a manuscript “On the Changing Seasonality over the North Pacific,” by Steven Bograd, Franklin Schwing, Roy Mendelssohn, and Phaedra Green-Jessen. The manuscript is in press in Geophysical Research Letters.
Background: Although many marine organisms, and specifically commercial fish species, have life histories adapted to seasonal events in the environment, most studies aimed at understanding biotic responses to environmental variability assume a stationary and deterministic seasonal cycle, or remove it altogether. However, if the seasonal cycles of physical forcing are changing on climate time scales, they may be driving shifts in the seasonal timing of ecosystems. This will impact recruitment and migratory patterns in fishery populations.
Purpose of Activity/Goal of Project: We examined atmospheric sea level pressure (SLP) data for the period 1948-2000 to document significant changes in the amplitude and phase of the seasonal cycle in the Aleutian Low and North Pacific High, the two dominant pressure centers over the north Pacific Ocean. These SLP systems are associated with the surface winds that drive upper ocean circulation processes and control a number of ecological activities.
Description of Accomplishment and Significant Results: The seasonal cycles of both SLP systems were found to have changed substantially since 1948. The Aleutian Low seasonal amplitude, which is dominated by the annual component, has nearly doubled over the past 50 years, mostly due to wintertime deepening. Changes in the amplitude and phase of both the annual and semi-annual components have contributed significantly to the time-varying structure of the North Pacific High. Changes in the phase and amplitude of the seasonal cycle are superimposed on, and in fact appear to be large contributors to, low-frequency climate fluctuations. These changes are not local phenomena, but appear to be linked to global atmospheric teleconnections of climate change.
Significance of Accomplishment (e.g., to the Center, to Management, and to NMFS Strategic plan Goals): Observed long-term changes in the biological community structure and productivity of the north Pacific Ocean may be associated with this changing seasonality. The evidence for a global teleconnectivity of seasonal atmospheric forcing suggests a mechanism for global synchrony of fluctuations in fishery populations.
Problems: None.
Key Contact: Franklin B. Schwing (831-648-9034; Frank.Schwing@noaa.gov)