The transition zone chlorophyll front, a dynamic global feature defining migration and forage habitat for marine resources

Pelagic ecosystem dynamics on all temporal scales may be driven by the dyna mics of very specialized oceanic habitats. One such habitat is the basin-wi de chlorophyll front located at the boundary between the low chlorophyll su btropical gyres and the high chlorophyll subarctic gyres. Global satellite maps of surface chlorophyll clearly show this feature in all oceans. In the North Pacific, the front is over 8000 km long and seasonally migrates nort h and south about 1000 km. In the winter this front is located at about 30- 35 degreesN latitude and in the summer at about 40-45 degreesN. It is a zon e of surface convergence where cool, vertically mixed, high chlorophyll, su rface water on the north side sinks beneath warm, stratified, low chlorophy ll water on the south side. Satellite telemetry data on movements of logger head turtles and detailed fisheries data for albacore tuna show that both a pex predators travel along this front as they migrate across the North Paci fic. The front is easily monitored with ocean color satellite remote sensin g. A change in the position of the TZCF between 1997 and 1998 appears Lo ha ve altered the spatial distribution of loggerhead turtles. The position and dynamics of the front varied substantially between the 1998 El Nino and th e 1999 La Nina. For example, from May to July 1999 the transition zone chlo rophyll front (TZCF) remained between about 35 degreesN and 40 degreesN lat itude showing very little meandering, whereas in 1998, during the same peri od, the TZCF exhibited considerable meandering and greater monthly latitudi nal movement. Catch rates for albacore were considerably higher in 1998 tha n in 1999, and we hypothesize that a meandering TZCF creates regions of con vergence, which enhances the foraging habitat for apex predators along the front. Published by Elsevier Science Ltd.