Instabilities and Vertical Flux Along
the Cyclonic Front of a Filament

John Ryan, Francisco Chavez
(MBARI)

Meandering jets force vertical motions in the atmosphere and ocean. In the Gulf Stream system, along-isopycnal upwelling of ~60 meters/day can occur as waters traverse meanders of the current (Bower and Rossby, 1989). High biological productivity in the upper water column has been associated with this along-isopycnal upwelling in the Gulf Stream, a meandering jet (Hitchcock et al., 1993). Enhanced phytoplankton biomass has also been observed in association with isopycnal upwelling along the shelf-break front off the northeastern United States (Ryan, et al. 1999). This upwelling is forced by the dynamics of the meandering shelf-break frontal jet. Off the southeastern United States, frontal eddies between the Gulf Stream and continental shelf pump nutrients into near-surface waters, fueling high primary production (Yoder et al., 1981). Frontal dynamics over the shelf strongly influence the distributions of phytoplankton biomass (Ryan et al. 1996). Frontal instabilities (meanders and eddies) are important dynamical processes that influence the vertical flux of dissolved and particulate material in upper ocean biogeochemical processes.

Off the California coast, frontal instabilities develop along the cyclonic (southern) boundary of upwelling filaments, and local upwelling of ~ 30 meters/day occurs in association with these instabilities (Washburn and Armi, 1988). However, the biological effects of this upwelling have not been studied. Such strong local upwelling along the filament interior would significantly impact the cycling of nutrients and particles within the evolving filament. Understanding these frontal processes requires combined high-resolution observation of frontal structure both within the water column and at the surface. Such observations would be best performed by AUVs and aircraft, respectively. The AUV sampling pattern useful for mapping the filament would serve well to examine frontal structure and hydrographic/biological distributions. Within the limits of coverage (overpass/clouds), the SeaWiFS and AVHRR satellite observations would provide coarse (~1 km) resolution surface mapping of the evolving filament. In order to capture the synoptic high-resolution surface structure of the filament frontal boundaries, we also conducted an ER-2 aircraft overflight with the AVIRIS instrument.   For information on the AVIRIS instrument, see http://makalu.jpl.nasa.gov/aviris.html.

Bibliography
Bower, A. S. and T. Rossby. 1989. "Evidence of cross-frontal exchange processes in the Gulf Stream based on isopycnal float data", Journal of Physical Oceanography 19:1177-1190.

Hitchcock, G. L. et al. 1993. "Mesoscale pigment fields in the Gulf Stream: observations in a meander crest and trough", Journal of Geophysical Research 98:8425-8445.

Ryan, J. P. and J. A. Yoder. 1996. "Long-term mean and event-related pigment distributions during the unstratified period in South Atlantic Bight outer margin and middle shelf waters", Continental Shelf Research 16:1165-1183.

Ryan, J. P., J. A. Yoder, P. C. Cornillon, and J.A. Barth. 1999. "Chlorophyll enhancement and mixing associated with meanders of the shelfbreak front in the Mid-Atlantic Bight", Journal of Geophysical Research, 104: 23,479-23,493.

Washburn, L. and L. Armi. 1988. "Observations of frontal instabilities on an upwelling filament", Journal of Physical Oceanography, 8:1075-1092.

Yoder, J. A. et al. 1981. "Role of Gulf Stream frontal eddies in forming phytoplankton patches on the outer southeastern shelf", Limnology and Oceanography 26:1103-1110.

Data Index Aircraft AUV CODAR
Drifters Moorings Satellites Ships