ALBERT

Description: The mid-Holocene (6000 calibrated years before present) is a key period in palaeoclimatology because incoming summer insolation was lower than during the late Holocene in the Southern Hemisphere, whereas the opposite happened in the Northern Hemisphere. However, the effects of the decreased austral summer insolation over South American climate have been poorly discussed by palaeodata syntheses. In addition, only a few of the regional studies have characterised the mid-Holocene climate in South America through a multiproxy approach. Here, we present a multiproxy compilation of mid-Holocene palaeoclimate data for eastern South America. We compiled 120 palaeoclimatological datasets, which were published in 84 different papers. The palaeodata analysed here suggest a water deficit scenario in the majority of eastern South America during the mid-Holocene if compared to the late Holocene, with the exception of northeastern Brazil. Low mid-Holocene austral summer insolation caused a reduced land–sea temperature contrast and hence a weakened South American monsoon system circulation. This scenario is represented by a decrease in precipitation over the South Atlantic Convergence Zone area, saltier conditions along the South American continental margin, and lower lake levels.

Description: This work analyzes the relationship between climatic index and rainfall in the Northeastern (NE) and Southern (S) Brazil, in decadal timescale. The climatic indices were obtained from the reanalysis data from NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research) between 1948 and 2008. Subsequently, (indices and rainfall correlation coefficients derived from the GPCP (Global Precipitation Climatology Project) dataset were calculated using filtered and non-filtered time series, within the decadal frequency). The results show that ElNi ˜no Southern Oscillation (ENSO) is the main phenomenon influencing NE rainfall due to related changes in tropical circulation while the Intertropical Convergence Zone (ITCZ) annual cycle also affects rainfall in the NE to a lesser extent. Meanwhile, in the Southern region, the most important phenomenon is the Southern Annular Mode (SAM) which controls cyclones activity in mid-latitudes. The Tropical Atlantic dipole index (ADI) also influences the rainfall in the Southern, and this might be related to moisture being transported from the ocean to the continent, which is then carried to the South by the Low Level Jet. It is also suggested that the decadal variability of the Tropical Atlantic Ocean and its influence on the precipitation in NE andS regions of Brazil are episodic because no significant correlations were obtained at decadal frequency. Finally, the spectral analysis revealed that the interannual timescale is the main frequency of variability in both studied regions, affecting differently each one of them. RESUMO: Este trabalho analisa as relações entre índices climáticos e a precipitação no Nordeste (NE) e Sul (S) do Brasil, em escala decadal. Os índices climáticos foram obtidos a partir de dados da reanálise do NCEP/NCAR (National Center for Environmental Prediction/National Center for Atmospheric Research), para o período de 1948 a 2008. Posteriormente, foram obtidos os coeficientes de correlação entre os índices e as anomalias de precipitação advindas do banco de dados do GPCP (Global Precipitation Climatology Project) nestas regiões, utilizando séries não filtradas e séries filtradas na frequência decadal. Os resultados sugerem que o principal fenômeno que modula a precipitação no NE é o El Ni˜no-Oscilação Sul (ENOS), devido às alterações na circulação tropical, e também o ciclo anual da Zona de Convergência Intertropical (ZCIT), que modula a estação chuvosa do NE. Na região S, o fenômeno que mais influencia a precipitação em escala decadal é o Modo Anular Sul (SAM),por modular a atividade ciclogenética em latitudes médias, além do índice do dipolo do Atlântico Tropical (DA), que pode estar ligado ao aporte de umidade oceânica para o continente, e levada ao S pelo jato de baixos níveis. Também se sugere que a variabilidade decadal do Atlântico tropical e sua influência na precipitação no NE sejam episódicas, e não periódica, já que não foram obtidas correlações importantes para este índice, na frequência estudada. Finalmente, a análise espectral revelouque a escala interanual é a principal frequência de variabilidade temporal em ambas as regiões, com efeitos diversos em cada uma delas.Palavras-chave: precipitação, ENOS, Atlântico, SAM.