Abstract
Ocean Colour (OC) sensors have been primarily used in biological studies. More recently, OC information has been attracting the attention of oceanographers, as a potential method for revealing physical structures in the ocean. In this study, OC data obtained from SeaWiFS imagery is used, for the first time, to detect the weak Azores Current (AzC) and the associated Azores Front (AzF). Previous studies show that the frontal interface is well seen on SST imagery only during the cold season, while it is disguised during the warm season through the formation of a strong seasonal thermocline. With SeaWiFS imagery, the frontal interface is well identified around 34° N as an asymmetric zonally stretched band of higher near-surface chlorophyll a (CHL a) values north of the AzF, accompanied by a sharp decrease to the south. Quasi-stationary meanders, previously derived from SST fields for the same region, are also well observed in OC imagery. Monthly-averaged Chl a along a meridional cross-section shows that, from spring to autumn, the front is clearly visible. In winter, differences across the front are less pronounced, and the front is more easily identified on SST fields. OC gradients weaken to the east, corresponding to the general weakening of the AzC. In situ CTD data reveal a sharp and meandering thermohaline and dissolved oxygen front ocated at 33-34.5° N and 31° W. This study suggests that OC imagery, combined with other sensors, provide an important tool to investigate ocean dynamic variability, by helping to detect frontal zones with great precision.