Improving Understanding of Variability in the
California Current Upper Ocean Structure

Current Status of Accomplishment or Milestone: Completed.

Background: Dramatic declines in the biological production of the California Current (CC) ecosystem over the past several decades have been attributed to changes in the upper ocean structure. This lower productivity may be reflected in declining fishery populations. Despite this evidence, little effort has been placed on characterizing multi-decadal changes in upper ocean structure and thermal stratification in the CC. PFEL research has built sequentially toward a better understanding of the mechanisms by which climate variability is exhibited in upper ocean conditions and ultimately marine populations.

Purpose of Activity/Goal of Project: Scientists at PFEL developed and applied state-space models to detect and characterize changes in the long-term trends and seasonality of ocean temperature and thermal stratification in the upper 200 m of the CC over the period 1950-1993.

Description of Accomplishment and Significant Results: Long-term increases in stratification and a deepening of the thermocline in the coastal CC over the past 50 years implies that nutrient input to the photic layer and overall productivity has declined over time. The magnitude and timing of the seasonal cycle of thermocline strength and depth varies as well, potentially affecting the ambient conditions for seasonal upwelling and the timing of biological cycles in the CC. Two recent peer-reviewed manuscripts describing these results have been published in the Journal of Geophysical Research; “Non-stationary seasonality of upper ocean temperature in the California Current”, and “Long-term and seasonal trends in stratification in the California Current, 1950-1993”.

Significance of Accomplishment (e.g., to the Center, to Management, and to NMFS Strategic plan Goals): This analysis has produced a set of leading environmental indicators for the FATE program. These are currently being used to force lower trophic models for the CC, and will be tested for their utility in explaining past variability in CC fish populations. This continuing work will improve our understanding of how oceanographic changes in the CC affect resource populations and ecosystem structure and production, and ultimately advance our ability to forecast future regime shift effects.

Problems: None.

Key Contact: Franklin B. Schwing (831-648-9034, franklin.schwing@noaa.gov)