Quantifying eddy–chlorophyll covariability in the Coastal Gulf of Alaska

Abstract

Many analyses of the interaction between ocean physics and biology in the Coastal Gulf of Alaska (CGOA) resolve chlorophyll variability separately from eddy-induced circulation, but eddy–chlorophyll covariability has not received much attention. The present research quantified eddy–chlorophyll interaction from the covariability of observed chlorophyll and eddy kinetic energy (EKE) in the CGOA for 1998–2002. Analyses with coupled empirical orthogonal functions (CoEOFs) showed that covariability between the two fields resulted in strongly coupled modes—a feature absent from standard-EOF analyses. Timescales of covariability were also incorporated into the analyses. The temporal evolution of each CoEOF mode was decomposed with the cross-wavelet power spectrum, and instances of covariability for synoptic timescales (2–6 months) were attributed to eddy–chlorophyll interaction. Further analyses in the present research included CoEOF decomposition for the output of a coupled physical–biological model in the CGOA. Model-observation comparisons with CoEOFs offer a new and important way to evaluate coupled models for eddy–chlorophyll interaction across multiple temporal and spatial scales. Implications for cross-shelf transport and spatiotemporal sampling for both observation and model data fields are also discussed.