Evidence for enhanced primary production resulting from relative vorticity induced upwelling in the Catalan Current
Keywords:vorticity, meanders, Catalan Current, new production, primary production
In baroclinic fronts, jets and eddies, potential vorticity, P = (V + f) / D, connects horizontal motions of planetary vorticity, f, and relative vorticity, V, to vertical transport through increases and decreases of the water column height, D. In this paper we present evidence that positive changes in relative vorticity of the SW flowing Catalan Current and meandering of the coastal jet follow the 500 m isobath and are associated with topographic steering by offshore canyons. Generally, positive relative vorticity is a result of cyclonic torque that generates cyclonic flow causing the water column to upwell since both P and the volume of the flow are conserved. With coastal jets that flow over abrupt topographies, such as deep canyons, D increases and flow must take on a cyclonic circulation, favoring upwelling conditions. In the case of a westward flowing current, we would expect the flow to acquire a cyclonic vorticity upstream of the canyon but to enter at the canyon obliquely (Cushman-Roisin, 1994) causing downwelling. Upwelling in meandering coastal jets can also occur when horizontal streamlines diverge, unable to adjust to relative vorticity changes, and fluid parcels near the edge of the front separate. Using pycnocline thickness as an indicator of D, we show that deep canyons stretch the water column causing cyclonic meandering (positive relative vorticity), upstream of the canyon during the FRONTS cruises 1991 to 1993. This phenomena has been shown to cause upwelling upstream of meander troughs (Onken, 1992) which in this case would mean upstream of canyons. We hypothesize that the increased relative vorticity, associated with upwelling in the pycnocline, fuels episodic primary production across the front accounting for more than 30% of the new production in this coastal zone.
How to Cite
Copyright (c) 2004 Consejo Superior de Investigaciones Científicas (CSIC)
This work is licensed under a Creative Commons Attribution 4.0 International License.© CSIC. Manuscripts published in both the printed and online versions of this Journal are the property of Consejo Superior de Investigaciones Científicas, and quoting this source is a requirement for any partial or full reproduction.
All contents of this electronic edition, except where otherwise noted, are distributed under a “Creative Commons Attribution 4.0 International” (CC BY 4.0) License. You may read here the basic information and the legal text of the license. The indication of the CC BY 4.0 License must be expressly stated in this way when necessary.
Self-archiving in repositories, personal webpages or similar, of any version other than the published by the Editor, is not allowed.