Glacial variations of mineral dust in comprehensive climate model simulations

Abstract

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.