Phytoplankton Variability in Eastern Boundary Currents: Connections to Physical Forcing

Overview and Introduction:
Coastal upwelling of nutrient rich subsurface water makes eastern boundary currents (EBCs) among the most biologically productive regions of the global ocean. The California, Canary, Peru/Chile and the Benguela Current regimes each have highly productive and commercially valuable fisheries. The wind driven upwelling and resultant hydrographic and biological patterns appear to be coupled with the large scale flow in a complex and still undetermined manner (Strub et al. 1991). All three processes have marked seasonal and latitudinal variability. Superimposed on this variability are strong interannual differences imposed on the system via non-local forcing (Hill et al. 1997). Quantification and separation of these linkages is difficult with traditional sampling strategies due to the wide range of time / space scales involved. Satellite data provide the ability to identify the scales at which linkages occur, the times and/or latitudes where variability is maximum and the locations where climate change induced variability might preferentially act or present the strongest signal. This is the first step towards effective application or design of both process oriented studies and measurement / monitoring schemes.

Research Specifics:
We provide a systematic comparison of the relationships between physical forcing and biological response between the four major EBC regimes of the globe, the California Current, Canary Current, Peru/Chile Current and Benguela Current, based on EOS era satellite data products. We have built the biological analysis and biological-physical coupling component onto ongoing analyses of physical variability in EBCs, strongly leveraging the required funding. In each region, we form coincident, co-registered and appropriately subset satellite derived geophysical fields and calculate statistical relationships in time and space between them. The primary goal is to identify the dominant modes of variability in each EBC region, providing quantitative linkages between the basin / interannual scales and local / event scales. Analysis begun with event scale relationships and associated coupling and variability and progresses to seasonal and interannual variability as the period of available data increases. We use our previous experience and continuing investigations of patterns and relationships in the California Current System to pose hypotheses and as a basis for comparison.