Seasonal and ENSO-related ocean variability in the Panama Bight

In the Panama Bight, a reverse seasonal surface circulation coincides with a strong mean sea level variation, as observed from 27 years of Absolute Dynamic Topography (ADT) and the use of Self-Organizing Maps. From January to April, a cyclonic gyre dominates the basin circulation, forced by the Panama surface wind jet that also produce upwelling, reducing Sea Surface Temperature (SST) and increasing Sea Surface Salinity (SSS), causing an ADT decrease. From June to December, the Choco surface wind jet enhances SST, precipitation and river runoff, which reduces SSS causing an ADT rise, which forces a weak anticyclonic circulation. Interannual variability in the region is strongly affected by ENSO, however this climatic variability does not modify the seasonal circulation patterns in the Panama Bight. On the contrary, ENSO positive (negative) phase increases (decreases) SST and ADT in the Panama Bight, with a mean annual difference of 0.9 °C and 9.1 cm respectively between the two conditions, while its effect in SSS is small. However, as the strong seasonal SST, SSS and ADT ranges are up to 2.2 °C, 2.59 gr kg-1 and 28.5 cm, the seasonal signal dominates over interannual variations in the Bight.