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<p>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^-1in 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^-1and 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.</p><div> </div>

Entre el 6 y el 11 de febrero del 2012, se realizó un levantamiento hidrográfico y batimétrico en la región situada entre Punta Guiones y Cuajiniquil, en el Pacífico norte de Costa Rica. Las temperaturas superficiales se ubicaron entre los 25.5 y 27.5°C, y el rango salino superficial estuvo entre 33.2 y 33.8 PSU. La termoclina se localizó a los 20 m en el extremo norte de la región, mientras que en el extremo sur, desde Ostional hasta Guiones, se observó ligeramente más profunda, alrededor de los 25 m. El espesor de la capa de mezcla fue de 10 m en toda el área estudiada. Dos giros, uno ciclónico y otro anticiclónico, se registraron en la región frente a Ostional. Los estratos superficiales estuvieron ocupados por el Agua Superficial Tropical (AST), con salinidades inferiores a 34 PSU y temperaturas superiores a 26°C, y los niveles intermedios (~ 50 m), por el Agua Subsuperficial Subtropical (ASS), caracterizada por un núcleo salino cercano a las 35 PSU. La batimetría de la región muestra isóbatas paralelas a la costa, con una elevación alrededor de los 20 m de profundidad en el extremo sur de la zona estudiada. El grado de inclinación o pendientes no sobrepasaron los 14.5°. Abstract Between February 6 and 11, 2012, a hydrographic cruise and bathymetric sounding were conducted in the region located between Guiones and Cuajiniquil, in the Northern Pacific area of Costa Rica. The range of surface temperatures is 25.5 to 27.5°C, and the saline surface ranges between 33.2 and 33.8 PSU. The thermocline is located at 20 m at the northern end of the region, while at the southern end, from Ostional up to Guiones, it was observed slightly deeper, approximately 25 m deep. The thickness of the mixed layer was 10 m in virtually all the studied area. Two gyres, one cyclonic and another anticyclonic, were observed in front of Ostional. The surface layers were occupied by the Surface Tropical Water (STW), with salinities below 34 PSU and temperatures greater than 26°C, and the intermediate levels (~ 50 m) by the Subsurface Subtropical Water (SSW), characterized by a saline core near 35 PSU. The bathymetry of the region shows isobaths parallel to the coast, with an elevation close to 20 m deep at the southern end of this area. The degree of inclination did not exceed 14.5°.