The impacts of Amazon deforestation on climate change are investigated through the use of twin numerical experiments with an Atmospheric General Circulation Model (AGCM) with prescribed global sea surface temperature and the same AGCM coupled to an ocean GCM over the global-tropics (CGCM).An ensemble approach is adopted, with ten member ensemble-averages of a control simulation compared with perturbed simulations for three scenarios of Amazon deforestation. The latest 20 years of simulation from each experiment are analyzed. Local surface warming and rainfall reduction are simulated by both models over the Amazon basin, with the coupled model presenting rainfall reduction that is nearly 60% larger compared to its control run than those obtained by the AGCM. The results also indicated that both the fraction of the deforested area and the spatial continuity of vegetated area might be important for modulating global climate variability and change. Additionally, significant remote atmospheric responses to Amazon deforestation scenarios are detectable for the coupled simulations, which revealed global ocean and atmosphere circulation changes conducive to enhanced ocean-atmosphere variability over the Pacific Ocean. This, in turn, is interpreted as a manifestation of enhanced El Niño-Southern Oscillation (ENSO) activity over the Pacific and a positive feedback contributing to the extra rainfall reduction over the Amazon on the coupled simulations.

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[1] The temporal evolution of the coupled variability between the South Atlantic Convergence Zone (SACZ) and the underlying sea surface temperature (SST) during austral summer is investigated using monthly data from the NCEP/ NCAR reanalysis. A maximum covariance analysis shows that the SACZ is intensified [weakened] by warm [cold] SST anomalies in the beginning of summer, drifting northward. This migration is accompanied by the cooling [warming] of the original oceanic anomalies. The results confirm earlier analyses using numerical models that suggest the existence of a negative feedback between the SACZ and the underlying South Atlantic SST field. A linear regression of daily anomalies of SST and omega at 500 hPa to the equations of a stochastic oscillator reveals a negative ocean -atmosphere feedback in the western South Atlantic, stronger during January and February directly underneath the oceanic band of the SACZ. Citation:

[1] The western Equatorial Undercurrent (EUC) and North Equatorial Countercurrent (NECC) are investigated at 38°W using contemporaneous subsurface (ADCP) and high-resolution near-surface (drifters + satellite altimeter) velocity measurements, together with hydrographic (CTDO 2 ) data that were collected from 1998 to 2006. The observations reveal an EUC with a strong semiannual pattern of intensification. Direct measurements also confirm the existence of a northern branch of the NECC (nNECC), observed here for the first time in the western tropical Atlantic. The NECC displays an annual cycle of northward migration on the basin, driven by the Sverdrup transport generated by the wind field. In this cycle the nNECC is a semipersistent feature fed by waters from the Northern Hemisphere and the residual nNECC flow from the previous year.

The biogeochemical dynamics of carbon in the ocean is a subject of fundamental interest to environmental studies. In this context, we have implemented a ten year run of the Brazilian Earth System Coupled Ocean-Atmosphere Model (BESM-OA2.3) integrated with TOPAZ biogeochemical model for the Atlantic basin. The modeled ΔpCO 2 for the tropical Atlantic shows very clearly a high dominance of positive fluxes, that is, the CO 2 fluxes are sea-to-air throughout the tropical region and for both winter and summer periods. In the mid-latitudes regions negatives fluxes (air-to-sea) were observed for both seasons. An exception to this pattern is an extensive negative tongue on the latitude 10˚N. The occurrence of this negative ΔpCO 2 tongue region in the Tropical Atlantic is highly correlated to negative Evaporation-Precipitation values during this season. In the northern hemisphere (NH) summer the negative values of ΔpCO 2 in the tropical Atlantic region are concentrated in the adjacent zone of the Amazon river mouth due to the North Equatorial Counter Current intensification. This process favors the formation of a carbon sink in the adjacent region of the Amazon river mouth. Model results show lowest values of dissolved inorganic carbon (DIC) in a surface layer (100-150 m). Highest DIC values are observed in deeper layers and concentrated in an equatorial band. The chlorophyll bloom in equatorial zones was well represented by the model. These blooms are the result of equatorial upwelling that brings the high concentration tongues of DIC present in the equatorial band towards the euphotic zone. This is the first published paper about the BESM-OA2.3 integrated with TOPAZ. The presented results suggest that this modeling system is able to reproduce the main regional carbon dynamics features of the mid-latitude/tropical Atlantic.