Multidecadal climate variability in Brazil's Nordeste during the last 3000 years based on speleothem isotope records

Abstract

We present the first high resolution, approximately ∼4 years sample spacing, precipitation record from northeastern Brazil (hereafter referred to as ‘Nordeste’) covering the last ∼3000 yrs from 230Th‐dated stalagmites oxygen isotope records. Our record shows abrupt fluctuations in rainfall tied to variations in the intensity of the South American summer monsoon (SASM), including the periods corresponding to the Little Ice Age (LIA), the Medieval Climate Anomaly (MCA) and an event around 2800 yr B.P. Unlike other monsoon records in southern tropical South America, dry conditions prevailed during the LIA in the Nordeste. Our record suggests that the region is currently undergoing drought conditions that are unprecedented over the past 3 millennia, rivaled only by the LIA period. Using spectral, wavelet and cross‐wavelet analyses we show that changes in SASM activity in the region are mainly associated with variations of the Atlantic Multidecadal Oscillation (AMO) and to a lesser degree caused by fluctuations in tropical Pacific SST. Our record also shows a distinct periodicity around 210 years, which has been linked to solar variability.

New Insights From Pre-Columbian Land Use and Fire Management in Amazonian Dark Earth Forests

“…Disentangling climate and pre-Columbian drivers of the late Holocene expansion of Mauritia/Mauritiella and other useful plants is complicated by the synchroneity of changes in regional climate (Baker et al, 2001b;Cruz et al, 2009;Novello et al, 2012;Wang et al, 2017) and the apex of pre-Columbian activity in lowland Amazon during this time (Roosevelt, 1999;Schaan, 2010Schaan, , 2012Gomes, 2011;Schaan et al, 2012;Stenborg et al, 2012). Paleoclimate records indicate an anti-phasing in regional precipitation patterns between the eastern Amazon and other areas of lowland South America (Baker et al, 2001b;Cruz et al, 2009;Novello et al, 2012;Wang et al, 2017). As many regions transition toward wetter conditions in the late Holocene (Baker et al, 2001a), the eastern Amazon exhibits the driest Holocene conditions after ∼2,000 cal yr B.P.…”

Groundwater isotopic data as potential proxy for Holocene paleohydroclimatic and paleoecological models in NE Brazil

“…Although calibration (against modern hydrometeorological data) and corrections (of long-term isotopic effects on moisture sources) are still discussed (Baker and Fritz, 2015;Moquet et al, 2016), these proxies are relevant, in term of time resolution, for detailed multidecadal and millenial variations of the SASM over the Nordeste (Cruz et al, 2009;Novello et al, 2012;Cheng et al, 2013), and contributed to describe the large scale drivers of SASM changes during the Holocene and the complexity of their interactions.…”

“…(SA) paleoclimatic reconstruction, available proxies are still considered to be sparse for the area if they are compared to records from Northern Hemisphere (Vuille et al, 2012;Prado et al, 2013a;.…”

“…Over the last two decades, the Holocene climate reconstructions for South-America Monsoon System (SASM) historically poor, have been subject to increasing investigation (Vimieux et al, 2009;Vuille et al, 2012;Prado et al, 2013a;Baker and Fritz, 2015). These reconstructions are based on combination of large-scale numerical models (e.g., IPSL-CM5A-LR, Kageyama et al, [2012] and references therein; MIROC-ESM, Watanabe et al…”

“…These proxies include dated pollens records (e.g., Oliveira et al, 1999;Auler et al, 2004), lake sediment geochemical analyses (e.g., Viana et al, 2014), terrigenous pulses in ocean cores (e.g., Arz et al, 1999), travertine deposits (e.g., Wang et al, 2004), tree rings (e.g., Ferrero et al, 2015), ice core δ 18 O variability investigations (mainly in the Andes; e.g., Thompson et al, 2013) and speleothem δ 18 O analyses (e.g., Cruz et al,2005;2009;Novello et al, 2012;Cheng et al,2013). However, despite the current increasing interest in the South America…”