Seasonal and intraseasonal variability of active and quiescent upwelling events in the Guajira system, southern Caribbean Sea

Abstract

The spatial and temporal variability of upwelling events occurring offshore northern Colombia (southern Caribbean Sea) on seasonal and intraseasonal time scales is analysed in detail for the period 01/1993–12/2015 using high-resolution oceanic and atmospheric reanalysis products. Different methods are applied that together allowed us to identify the upwelling and relaxation events observed in this area and to explain the main dynamic processes that occur within the annual cycle. In this region, the wind impulse directly determines the intensity and occurrence of upwelling. This upward motion can be full, with a clear surface signal during the months of intense northeast winds, or it can be partial during the rainy season, when winds weaken, and cold subsurface waters do not rise to the sea surface. There is evidence of onshore geostrophic flow affecting the Ekman dynamics when the wind impulse is low during the peak of the rainy season. Short-term atmospheric perturbations that interrupt the upwelling process for several days in La Guajira were characterised. On occasions, cold fronts associated with the intrusion of winds from the north (Nortes), and warm fronts associated with air masses coming from the eastern tropical Pacific, induce a favourable downwelling condition in the upper layer off La Guajira. During these short relaxation periods, the mixed layer is warm, and the relatively cold subsurface isotherms are located at greater depths due to the onshore transport of surface waters.