[1] The seasonal evolution of geostrophic currents in the Panama Bight is derived from satellite-borne altimeter data. Current literature describes the circulation in the Bight as being cyclonic only. Our study, instead, reveals two distinct seasonal patterns. In summer the circulation in the Panama Bight is anticyclonic, with a coastal current to the south, whereas in winter, the circulation reverses and is cyclonic with a coastal current to the north, and an oceanic upwelling center in the middle of the Bight. A seasonally changing wind field caused by the meridional migration of the Intertropical Convergence Zone, from 8 -10°N in summer, to about 2°N in winter, controls the circulation of the basin. In summer southeasterly trade winds dominate the region, but in winte rnortheasterly trade winds of the North Atlantic, by means of the Panama Jet, enter the region via the Isthmus of Panama.INDEX TERMS: 4532 Oceanography: Physical: General circulation; 4512 Oceanography: Physical: Currents; 4279 Oceanography: General: Upwelling and convergences. Citation: Rodríguez-Rubio, E., W. Schneider, and R. Abarca del Río, On the seasonal circulation within the Panama Bight derived from satellite observations of wind, altimetry and sea surface temperature, Geophys.

[1] Seasonal circulation and three-dimensional thermohaline structure within the Panama Bight are examined by employing satellite-derived sea surface winds and dense in-situ hydrographic datasets. The northerly Panama wind jet, associated with a dipole structure of wind stress curl that is positive (negative) on its eastern (western) flank, dominates the bight in winter. This wind jet generates a cyclonic eddy with mean geostrophic velocities of 60 cm s À1 , including the poleward flowing coastal Colombia Current, and induces a well pronounced thermocline dome. As a result, temperature (salinity) in the bight is much colder (saltier) than in its surrounding waters. Winds blow from southwesterly directions in summer and the bight is dominated by an anticyclonic eddy associated with a thermocline bowl. Mean geostrophic velocities are on the order of 40 cm s À1 and the Colombia Current is not observed. Temperature (salinity) in the bight is much warmer (fresher) than in its surrounding waters.

RESUMEN. La zona de influencia costera de isla Gorgona es un área marina protegida localizada en el Pacífico Oriental Tropical (POT) de Colombia. Aunque alberga uno de los arrecifes coralinos más desarrollados del POT, la caracterización de las condiciones oceanográficas superficiales locales y su variabilidad temporal y espacial han sido escasamente abordadas. Para incrementar el conocimiento sobre la variabilidad de la temperatura y la salinidad en esta localidad se realizaron registros sistemáticos de estas variables durante cuatro periodos (septiembre 2005, diciembre 2005, marzo 2006 y junio 2006), se instalaron sensores de registro continuo de temperatura a 15 m de profundidad en la zona oriental y occidental de la isla, y se realizó un monitoreo del patrón local de circulación superficial utilizando un perfilador de corrientes (AWAK-ADCP) durante junio 2006 y febrero 2007. Se identificaron dos períodos contrastantes para las condiciones oceanográficas en la capa superficial (0-50 m) de la columna de agua: un período cálido y de baja salinidad superficial entre mayo y diciembre (profundidad termoclina 47 m) y un período frío y salino entre enero y abril (profundidad termoclina 7,5 m). Se descartó la presencia de proceso local de surgencia y los resultados indicaron una fuerte influencia de procesos de mesoescala (surgencia en el Panamá Bight) sobre la variabilidad temporal de las condiciones oceanográficas en la zona de estudio. En este mismo sentido se sugiere que la variabilidad espacial estaría más asociada a procesos climáticos regionales (patrón de precipitación) y la cercanía de la zona de estudio al complejo deltaico río Patía -río Sanquianga.Palabras clave: temperatura, salinidad, oceanografía, isla Gorgona, Colombia, Pacífico Oriental Tropical. Oceanographic conditions off Gorgona Island, eastern tropical Pacific of ColombiaABSTRACT. The near shore zone of Gorgona Island is a protected marine area located in the Eastern Tropical Pacific (ETP) of Colombia. Although this is home to one of the most developed coral reefs in the ETP, the characteristics of the local oceanographic conditions at the surface and their spatial and temporal variability have been poorly studied. In order to increase the information on temperature and salinity variability off Gorgona Island, systematic records of these variables were made during four periods (September 2005, December 2005, March 2006, June 2006. Furthermore, continuous record temperature senors were installed at 15 m depth on the eastern and western sides of the island and the local surface circulation pattern was monitored in June 2006 and February 2007 using a current profiler (AWAC-ADCP). Two contrasting periods were identified in the oceanographic conditions of the surface layer (0-50 m): a warmer and low salinity period between May and December (thermocline depth 47 m), and a colder and high salinity period between January and April (thermocline depth 7.5 m). Local upwelling events were not observed and the results suggest a strong influence of mesoscale...

Variability of the oceanographic conditions in the Colombian Pacific Ocean, a part of the Panama Basin, is subjected to the variability of wind conditions in the equatorial part of the Pacific Ocean. Data of OCTS and NSCAT of ADEOS-I satellite provided as monthly averages for the period November 1996-June 1997 by NASDA, were processed and manipulated. A meridional (N-S) component and a zonal (E-W) component were run in order to analyse the data variability and correlation. It is concluded that the variability of the oceanic surface chlorophyll and SST in the Colombian Pacific is a seasonal event related to the migration of the ITCZ and the generation of a wind jet at the Isthmus of Panama. Upwelling due to the wind rotor is present throughout the whole period, with variable spatial distribution and a tendency to be located towards the eastern part of the basin. In a similar way, high chlorophyll concentrations observed in March coincide with both the intensification of the vertical velocities during that month, and the maximal rise of the thermocline in the northern part of the Panama Basin. Picture series of surface chlorophyll, SST, wind stress and Ekman pumping are provided for the studied area.

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