Seasonal and Interannual Mixed-Layer Heat Budget Variability in the Western Tropical Atlantic From Argo Floats (2007-2012)

Oceanic and atmospheric processes were investigated in order to explore the causes of seasonal and interannual variability of sea surface temperatures (SST) in the western tropical Atlantic (WTA; 20 degrees S-20 degrees N, 15 degrees W-60 degrees W). A mixed-layer (ML) heat budget was performed by using Argo profiles and supplementary data sets based on satellite and atmospheric products during the period 2007-2012. The WTA is divided into four boxes which represent the main temporal and spatial heterogeneities of this region. An analysis of error of each term pointed out that the mean net surface heat fluxes are systematically underestimated by 20 W m(-2). A correction of this term provides realistic estimates of the vertical mixing which was obtained as residual term. In agreement with previous studies, the results show that surface flux is the most important process that governs the seasonal cycle of the heat content. Changes in shortwave radiation and latent heat fluxes dictate the oceanic response to the meridional migration of the ITCZ. Along the equator, surface fluxes modulate the annual cycle of ML temperature, but are strongly balanced by horizontal advection. The entrainment term proves a small contribution to the cooling of the ML. On an interannual time scale, the strong positive (negative) SST anomalies observed in 2010 (2012) were generated during the previous winter in both years, mainly north of 10 degrees N, during which the wind anomalies were at the origin of intense heat loss anomalies. Horizontal advection may contributes to the maintaining of these SST anomalies in the equatorial zone and south Atlantic.