COLD-WATER FILAMENTS IN THE CALIFORNIA CURRENT SYSTEM

Prior to the mid 1980s, little was understood about the dynamics of cold filaments and their relation to coastal upwelling. However. during the late 1980s, the Coastal Transition Zone Programme studied these features in detail off California, leading to more information about their physical dynamics and their relation to ecosystem structure. First. the filaments are the surface signature of the offshore-flowing limbs of meanders in the core equatorward jet of the California Current. Modelling studies have shown that the core jet of the California Current is hydrodynamically unstable, leading to these meanders and to the separated eddies which surround the meandering jet. This process of instability has nothing directly to do with the wind field, so it appears that the fundamental dynamics of filaments has little to do with either coastal upwelling or meteorological forcing. Second, it could be asked why a continuous jet does not appear as a continuous meandering band in sea surface temperature or enhanced chlorophyll. The explanation is that water proceeding offshore in a filament subducts at a rate of the order of 10 m.day-1. Therefore, the sea surface signature of the filament is removed before the jet can tum back toward the coast- Finally, observations of phytoplankton and zooplankton community structure demonstrate that the core of the meandering jet represents a continuous ecological boundary.