This study was conducted in the southeast region of the Central American Pacific, an area of great oceanographic importance due to the presence of various upwelling phenomena and the direct influence of the ENSO on its waters. Its main objective was to contribute to the knowledge of the main factors that modulate the regional dynamics. We describe the geostrophic circulation and thermohaline features along two transects obtained in October 2010 and March 2011, one from Costa Rica at (84°54’ W - 9°37’ N) to the SW of Cocos Island at (88°19’ W - 3°06’ N), and the second oriented zonally across the island from (88°14’ W - 5°33’ N) to (84°33’ W - 5°33’ N). Surface temperatures ranged from 27°C to 29°C and a near isothermal layer, with an average thickness of 40 m, was apparent above the thermocline centered at 60 m. Surface salinities were between 32 and 32.8, typical values of the Tropical Surface Water. In both years, Cocos Island was located in a region of low surface salinities (~32). The salty core of the Subtropical Subsurface Water (~35) was located at an average depth of 150m. In October the circulation between Cocos Island and the continent was dominated by the presence of the North Equatorial Countercurrent (NECC), with speeds above 40 cm s-1 in the upper 50 m of the water column. No flow to the northwest near the coast that could be associated with the Costa Rica Coastal Current (CRCC) in October was observed. The Cocos Island was located in the center of a 150 m deep, 100 km diameter anticyclonic eddy, with surface speeds of 10 cm s-1and 20 cm s-1. In March the study area was again dominated by an anticyclonic cell, with eastward flow between 50 cm s-1 and 60 cm s-1 located between 200 km north and 100 km south of the island. The southern end of this cell, with velocities between 10 cm s-1 and 50 cm s-1 to the northwest, was located 200 km south of Cocos Island. A flow to the NW near the edge of the continental shelf, consistent with the CRCC, was observed in May. Our study contributes to document the oceanography of the eastern end of the Equatorial Current System near the coast of Central America, where regional forcing modifies the zonal flow which prevails west of the study area.
AVISO (2014). SSALTO/DUACS User Handbook: (M) SLA and (M) ADT Near-Real Time and Delayed Time Products, CLS-DOS-NT-06-034. Paris, France: Centre National d´Études Spatiales.
Amador, J., Alfaro, E., Lizano, O., & Magaña, V. (2006). Atmospheric forcing in the Eastern Tropical Pacific: A Review. Progress in Oceanography, 69, 101-142.
Ballestero, D., & Coen, J. (2004). Generation and propagation of anticyclonic rings in the Gulf of Papagayo. International Journal of Remote Sensing, 25, 2217-2224.
Brenes, C. L. (1983). Condiciones de Movimiento Geostrófico en el área del Domo Térmico de Costa Rica. Ciencia y Tecnología, 7(1), 121-152.
Brenes, C., Lavín, M., & Mascarenhas, A. (2008). Geostrophic circulation between the Costa Rica Dome and Central America. Deep-Sea Research I, 55, 608-629.
Chelton, D. B., DeSzoeke, R. A., Schlax, M. G., Naggar, K. E., & Siwertz, N. (1998). Geographical variability of the first baroclinic Rossby radius of deformation. Journal of Physical Oceanography, 28, 433-460.
Chelton, D., Schlax, M., Freilich, M., & Milling, R. (2004). Satellite measurements reveal persistent small-scale features in ocean winds. Science, 303, 978-983.
Díaz, J., & Neshyba, S. (1985). Manifestaciones de El Niño 1982-1983 en el trayecto Nicoya - Isla de El Coco. Uniciencia, 2(1), 53-56.
Fiedler, P. (1992). Seasonal climatologies and variability of Eastern Tropical Pacific surface waters. NOAA Technical Report NMFS 109, 70 pp.
Fiedler, P. (2002). The annual cycle and biological effects of the Costa Rica Dome. Deep-Sea Research I, 49, 231-338.
Fiedler, P., & Talley, L. (2006). Hydrography of the eastern Pacific: a review. Progress in Oceanography, 69, 143-180.
Hansen, D., & Maul, G. (1991). Anticyclonic current rings in the eastern tropical Pacific Ocean. Journal of Geophysical Research, 96, 6965-6979.
Hsin, Y., & Qiu, B. (2012). Seasonal fluctuations of the surface North Equatorial Countercurrent (NECC) across the Pacific basin. Journal of Geophysical Research, 117, 1-17.
Ichii, T., Mahapatra, K., Watanabe, T., Yatsu, A., Inagake, D., & Okada, Y. (2002). Occurrence of jumbo flying squid Dosidicus gigas aggregations associated with the countercurrent ridge o the Costa Rica Dome during 1997 El Niño and 1999 La Niña, Marine Ecology Progress Series, 231, 151-166.
Kessler, W. (2002). Mean three-dimensional circulation in the northeast tropical Pacific. Journal of Physics Oceanography, 32, 2457-2471.
Kessler, W. (2006). The circulation of the Eastern Tropical Pacific: a review. Progress in Oceanography, 69, 181-217.
Lizano, O. (2008). Dinámica de aguas alrededor de la Isla del Coco, Costa Rica. Revista de Biología Tropical, 56(Supplement 2), 31-48.
Murillo, L. M. (1990). La circulación de las Mareas en el Golfo de Nicoya. Tecnología en Marcha, 10(4), 51-76.
Sprintall, J., Kennan, S., Kim, Y., & Niller, P. (2009). Wind-Driven ageostrophic transport in the North Equatorial Countercurrent of the eastern Pacific at 95° W. Journal of Physical Oceanography, 39, 2985-2998.
Trasviña, A., & Andrade, C. (2002). Circulación Costera del Pacífico Tropical Oriental, con énfasis en la Cuenca Cálida Mexicana. En Circulación oceánica y climatología tropical en México y Colombia. Diálogo entre Pares 1 (pp. 9-37). Bogotá, Colombia: Consejo Nacional de Acreditación - Ministerio de Educación, Corcas.
Tsuchiya, M. (1975). Subsurface countercurrents in the eastern equatorial Pacific. Journal of Marine Research, 33(l), 145-175.
Tsuchiya, M., & Talley, L. (1998). A Pacific hydrographic section at 88° W: water-property distribution. Journal of Geophysical Research, 103, 12899-12918.
Wyrtki, K. (1965). Surface currents of the eastern tropical Pacific Ocean. Inter-American Tropical Tuna Commission Bulletin, 9(5), 271-304.
Wyrtki, K. (1966). Oceanography of the Eastern equatorial Pacific Ocean. Oceanography and Marine Biology: Annual Review, 4, 33-68.
Xie, S., Haiming, X., Kessler, W., & Masami, N. (2005). Air-sea interaction over the Eastern Pacific Warm Pool: Gap winds, thermocline dome, and atmospheric convection. Journal of Climate, 18, 5-20.