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A late Holocene paleoclimate reconstruction from Boqueirao Lake sediments, northeastern Brazil

Abstract : Lake level fluctuations and environmental changes during the late Holocene were inferred from changes in sedimentology, bulk and isotope organic geochemistry, and a diatom based transfer function in a sediment core from Boqueirao Lake, northeast Brazil. The age-depth model was established using fifteen AMS 14C dates. Lake water level began increasing about AD 400, and reached its maximum during the Medieval Climate Anomaly (MCA), AD similar to 900-1100. Low lake water level was recorded during the Little Ice Age (LIA), AD similar to 1400-1820, which allowed macrophyte development in the littoral zone that was recorded by high Corg/Ntotal ratios. Considerable lake level variability was evident during the Current Warm Period (CWP). Humid/dry conditions in northeast Brazil during MCA/LIA, respectively, are related to the southward shift of Inter-Tropical Convergence Zone (ITCZ) during austral summer and fall. Those conditions contrast with records of a decrease/increase in the South American Summer Monsoon (SASM) during these periods. This observation also contrasts with paleoclimate inferences from the circum-Caribbean region indicating a northward shift of the ITCZ northern hemisphere summer position during the MCA and a southward shift during the LIA. We suggest that these shifts in ITCZ seasonality were higher during the MCA and smaller during the LIA. Our aim was to answer whether the zonal atmospheric circulation cell between the Amazon and northeast Brazil was responsible for antiphasing with the SASM. A strong monsoon over South America during the LIA reinforced convection upon Amazon, increasing the northeast low in the upper troposphere and large-scale subsidence over northeast Brazil and the Atlantic Ocean leading to a northward repositioning of the South Atlantic Subtropical Anticyclone. These factors in combination may have limited the southward seasonal shift of ITCZ, and they must have been responsible for drier conditions in northeast Brazil during the LIA.
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Submitted on : Friday, February 10, 2017 - 12:55:23 AM
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João Cláudio Cerqueira Viana, Abdelfettah Sifeddine, Bruno Turcq, Ana Luiza Spadano Albuquerque, Luciane Silva Moreira, et al.. A late Holocene paleoclimate reconstruction from Boqueirao Lake sediments, northeastern Brazil. Palaeogeography, Palaeoclimatology, Palaeoecology, 2014, 415 (no spécial), pp.117-126. ⟨10.1016/j.palaeo.2014.07.010⟩. ⟨ird-01464115⟩



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