Abstract
Eddies and fronts created by geostrophic balance between counter-rotating currents are hydrodynamic processes that concentrate or dilute plankton and suspended material by physical processes of accumulation, retention, or dispersion. Over Campeche Canyon, in the southern Gulf of Mexico, observations revealed an anticyclonic eddy, a cyclonic current off the continental shelf, and an associated thermal front in their common boundary. Along this front there was high Trichodesmium spp. occurrence. Three water masses were found in the upper 120 m layer: Caribbean Tropical Surface Water (CTSW), Caribbean Subtropical Underwater (CSUW), and Gulf Common Water (GCW). The frontal zone between the warm core and cyclonic circulation was observed below the hot summertime mixed layer. The presence of Trichodesmium spp. was associated with the front, indicating its influence on the distribution of this diazotrophic cyanobacterium that enters the Campeche Canyon region via modified CTSW. The associated phytoplankton was dominated by tropical oceanic species of diatoms and dinoflagellates, especially species of Ceratium.
Highlights
IntroducciónCampeche Canyon and De Soto Canyon are the two most important physiographic features of the Gulf of Mexico, but the hydrodynamic conditions associated with them have yet to be studied in detail
The T-S diagram of the upper 120 m layer of the study area shows that Caribbean Tropical Surface Water (CTSW) and Caribbean Subtropical Underwater (CSUW) are modified in the Gulf of Mexico
The current pattern observed in the area may have been generated by at least three factors: (1) the negative wind stress curl over the Gulf of Mexico, which is anticyclonic in the northeastern part of the gulf and cyclonic in the southwestern part (Gutiérrez-de Velasco and Winant 1996); (2) the friction of the current against the continental slope that generates bathystrophic upwelling (Hsueh and O’Brien 1971) and
Summary
IntroducciónCampeche Canyon and De Soto Canyon are the two most important physiographic features of the Gulf of Mexico, but the hydrodynamic conditions associated with them have yet to be studied in detail. It is assumed that these canyons govern the hydrodynamics and distribution of sediments, giving rise to microenvironments (Escobar-Briones et al 2008), and that they play an important role in the regional structure of currents (Salas-de León et al 2004). El Cañón de Campeche y el Cañón De Soto son los dos rasgos fisiográficos más importantes del Golfo de México. Se considera que estos cañones condicionan la hidrodinámica y la distribución de los sedimentos dando origen a micro ambientes (EscobarBriones et al 2008), y que juegan un papel importante en la estructura de las corrientes a nivel regional (Salas-de León et Ciencias Marinas, Vol 35, No 4, 2009 fronts created by geostrophic balance between counter-rotating currents are hydrodynamic processes that concentrate or dilute plankton and suspended material by physical processes of accumulation, retention, or dispersion (Franks 1992). The generation of subsurface eddies and their associated currents and fronts through eddy-continental slope interaction and canyons in the Gulf of Mexico, is a matter of special interest because this phenomenon could explain the occurrence of the unusually intense subsurface currents observed in the Gulf of Mexico (Oey and Zhang 2004) and of the seemingly related phytoplankton filaments
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