The Nature of the Cold Filaments in the California Current System

Data from the Coastal Transition Zone (CTZ) experiment axe used to describe the velocity fields and water properties associated with cold filaments in the California Current. Combined with previous field surveys and satellite imagery, these show seasonal vaxiability with maximum dynamic height ranges and velocities in summer and minimum values in late winter and early spring. North of Point Arena (between 39øN and 42øN) in spring-summer the flow field on the outer edge of the cold water has the chaxacter of a meandering jet, carrying fresh, nutrient-poor water from farther north on its offshore side and cold, salty, nutrient-rich water on its inshore side. At Point Arena in midsummer, the jet often flows offshore and continues south without meandering back onshore as strongly as it does faxther north. The flow field south of Point Arena in summer takes on more of the chaxacter of a field of mesoscale ddies, although the meandering jet from the north continues to be identifiable. The conceptual model for the May-July period between 36 øN and 42øN is thus of a surface jet that meanders through and interacts with a field of eddies; the eddies are more dominant south of 39øN, where the jet broadens and where multiple jets and filaments axe often present. At the surface, the jet often separates biological communities and may appeax as a barrier to cross-jet transport, especially north of Point Arena early in the season (March-May). However, phytoplankton pigment and nutrients are carried on the inshore flank of the jet, and pigment maxima axe sometimes found in the core of the jet. The biological effect of the jet is to define a convoluted, 100 to 400-km-wide region next to the coast, within which much of the richer water is contained, and also to carry some of that richer water offshore in meanders along the outer edge of that region.