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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. Highlights • We examined active/quiescent upwelling events in the La Guajira system at different scales. • High-resolution oceanic and atmospheric reanalysis were used in the three-dimensional analysis of upwelling. • Several indices were applied to identify the evolution of each upwelling event. • We provide further insights towards understanding the local mechanisms interrupting upwelling. [ABSTRACT FROM AUTHOR]

The long-term mean annual cycle and interannual variability of the mixed layer heat budget in the Caribbean Sea are quantified by using high resolution oceanic and atmospheric reanalysis products (the GLobal Ocean ReanalYsis and Simulations, GLORYS2V4, and ERA-Interim) for the period spanning from January 1993 to December 2015. In this region the mixed layer depth (MLD) is relatively shallow, oscillating spatially from 10 to 90 m, with maximum values observed during the dry season (December to March), and minimum values during the main rainy season (September to November). The highest MLD values are found in the northwestern part of the basin and the lowest in the Central and northern South American coastal region. The strength and location of greater MLD oscillations over the Caribbean Sea depend on the intensity of the zonal winds and the location of the Caribbean-Low Level Jet (CLLJ). At interannual timescales, reanalysis data shows that the MLD anomalies are associated with extreme phases of the El Niño Southern Oscillation (ENSO); however, low statistical correlation suggests that other factors, such as a Quasi-Biennial Oscillation (QBO), or a weak ENSO cycle with a 2-year periodicity, could influence this region, and induce changes in the depth of the mixed layer and in the heat budget within it. The seasonal ocean heat balance within the mixed layer ranges between −315 and 393 W m −2 in the Caribbean region (monthly means around ±60 W m −2 averaged over the entire domain). The net air-sea heat flux varies seasonally around ±60 W m −2 . Analysis of this term shows that during the dry season (rainy season), when the MLD is deep (shallow) the region loses (gains) heat, with net short wave radiation being the main gain, and the latent heat the main loss at seasonal and interannual timescales. The advection term is an order of magnitude less (monthly means from −2 to 7.5 W m −2 ) but has the highest values during the dry season in the northwest Caribbean Sea, when the winds and surface currents are intense. This term tends to provide small interannual heat variability (up to ±2 W m −2 ). The entrainment is almost negligible in its contribution to the budget. At interannual timescales this flux reduces the stored heat by up to ±1 W m −2 . It is noted that although the MLD is not so clearly related with ENSO, the heat stored in this layer is significantly modulated by El Niño/La Niña remote forcing, especially during the period spanning from 1992 to 2001 when intense ENSO events occurred and affected the air-sea fluxes, and the advection. The CLLJ influences both the MLD and the heat budget in the Caribbean Sea. This jet is being modulated by ENSO and other long-term oscillations. [ABSTRACT FROM AUTHOR]