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Changes in tropical precipitation over the past millennia have usually been associated with latitudinal displacements of the Intertropical Convergence Zone (ITCZ). Recent studies provide new evidence that contraction and expansion of the tropical rainbelt may also have contributed to ITCZ variability on centennial time scales. Over tropical South America few records point to a similar interpretation, which prevents a clear diagnosis of ITCZ changes in the region. In order to improve our understanding of the equatorial rainbelt variability, our study presents a reconstruction of precipitation for the last 3200 years from the Northeast Brazil (NEB) region, an area solely influenced by ITCZ precipitation. We analyze oxygen isotopes in speleothems that serve as a faithful proxy for the past location of the southern margin of the ITCZ. Our results, in comparison with other ITCZ proxies, indicate that the range of seasonal migration, contraction and expansion of the ITCZ was not symmetrical around the equator. A new NEB ITCZ pattern emerged based on the comparison between two distinct proxies that characterize the ITCZ behavior during the last 2500 years, with an ITCZ zonal pattern between NEB and the eastern Amazon. In NEB, the period related to the Medieval Climate Anomaly (MCA) was characterized by an abrupt transition from wet to dry conditions. These drier conditions persisted until the onset of the period corresponding to the Little Ice Age (LIA), representing the longest dry period over the last 3200 years in NEB. The ITCZ was apparently forced by teleconnections between Atlantic Multidecadal Variability and Pacific Decadal Variability that controlled the position, intensity and width of Walker cell over South America changing the ITCZ zonally, and sea surface temperature changes in both the Pacific and Atlantic, stretching/weaking the ITCZ-related rainfall meridionally over NEB. Wetter conditions started around 1500 CE in NEB. During the last 500 years, our speleothems document the occurrence of some of the strongest drought events for the last millennia, which drastically affected population and environment of NEB during the Portuguese colonial period. The historical droughts were able to affect the karst system, and led to significant impacts over the entire NEB region. [ABSTRACT FROM AUTHOR]

Changes in insolation driven by precession and obliquity are considered the major driver of tropical precipitation on orbital time scales, and responsible for vegetation and physical landscape changes during the Late Holocene over tropical South America. Here we investigate the environmental changes in the karst region of Chapada do Apodi - Northeastern Brazil (NEB), using a multi-proxy approach including carbon (δ13C), oxygen (δ18O) and strontium (87Sr/86Sr) isotopic analyses on speleothems from different caves, carbonate bedrock, and clastic cave deposits. This approach reveals that the balance between soil formation and erosion and their alternating impact on vegetation and precipitation changes occurred in response to variations in the position and intensity of the Intertropical Convergence Zone (ITCZ) over the region. The high δ13C and δ18O and low 87Sr/86Sr values at 4,200 yrs BP indicate a massive episode of soil erosion, resulting in the exposure of carbonate bedrocks over a large area of the karst terrain. This event marks the beginning of the Meghalayan chronozone, characterized as the aridification of this region, decline in soil production, drying out of underground drainages, and increased dominance of dry-adapted flora species, characteristic of a more open vegetation (caatinga). We investigated if the Holocene climatic changes affected human occupation in the NEB and found that the overall demographic course is virtually identical to the well-established curve characterized by population deflation during Middle Holocene. • The combined use of speleothem δ18O, δ13C and 87Sr/86Sr records for paleoenvironmental reconstruction. • Relative changes in soil turnover in response to ITCZ rainfall in Northeastern Brazil. • Evidences of hydrological changes in the ITCZ region from multiproxy cave records. • Increased aridification in Northeastern Brazil coincident with Meghalayan chronozone. • The 4.2 event as marker of abrupt changes in climate and its impact in human population. [ABSTRACT FROM AUTHOR]

Few high-resolution paleoclimate proxy records exist in the region located under the direct influence of the Intertropical Convergence Zone (ITCZ) in South America and most of them were retrieved from the Cariaco Basin off the coast of Venezuela. Here we present new ẟ18O and ẟ13C records of Venezuelan speleothems collected in caves adjacent to Cariaco, covering the mid- and late-Holocene. We document previously undetected secular-to multidecadal-scale climate variability in the core region of the ITCZ, which is compared to other high-resolution records from the North Atlantic, Caribbean and tropical South America. Over the mid-Holocene our record exhibits broad swings between periods of reduced (8.3–8.0, 6.5–5.0, 4.1–3.6 ka BP) and increased (8.5, 8.0–6.5, 4.9–4.2 ka BP) rainfall. In particular, between 5.5 and 5.0 ka BP, increases in polar and subpolar North Atlantic ice rafted debris and a reduction in North Atlantic Deep Water (NADW) formation might have contributed to the southward displacement of the North Atlantic Subtropical High (NASH) and the ITCZ, which led to severe dry conditions in north central Venezuela and an enhancement of the South American Monsoon System (SAMS). During the late-Holocene, contrary to data from Cariaco reported in previous studies, our results point to drier conditions during the Medieval Climate Anomaly (MCA, 900–1100 CE), which were further amplified during positive Atlantic Multidecadal Oscillation (AMO) phases. Wet conditions, however, prevailed during the first part of the Little Ice Age (LIA, 1400–1500 CE). No speleothem deposition occurred during the main LIA period, which might be related to drier conditions in response to a southward displacement of the ITCZ that led to major moisture convergence over the SASM domain. Our new records from Venezuela provide a reliable proxy for ITCZ behavior over the Atlantic – South America domain and document past dynamics in relation to other climate systems (NASH and SAMS), while providing new evidence of ITCZ – North Atlantic teleconnections during the Holocene. • ẟ18O and ẟ13C speleothem records from northern Venezuela for mid- and late- Holocene. • ITCZ meridional migration proxy nearby Cariaco Basin. • Evidence of IRD and NADW forcings on ITCZ rainfall between 6000 and 5000 years BP. • Northern Venezuela presents dry MCA and wet first part of the LIA. • MCA dry conditions further amplified during positive AMO phases. [ABSTRACT FROM AUTHOR]

The paleoclimatic and paleoenvironmental history of the Amazon basin over the last millennia and the behavior of the South American Monsoon System (SAMS) throughout the lowlands have not yet been thoroughly examined due to a lack of records from more central portions of the basin. Here we discuss these past changes based on new high-resolution δ18O and δ13C records from speleothems collected in the southwestern Amazon Basin, at the core region of the convective activity of the SAMS. We demonstrate that the δ18O from these new records is representative of SAMS variations and that this convective system provides distinct precipitation patterns over the basin. The SAMS was in a neutral phase with homogeneous precipitation between 1000 BCE and 300 CE, whereas drier conditions prevailed over the western side of the basin between 700 and 1200 CE and an east-west climatic dipole was established over the Amazon Basin after 1450 CE when wetter conditions prevailed over our study site. The speleothem δ13C record indicates an overall tendency toward a more humid tropical forest during the studied period, except for a drier period which correlates with the Medieval Climate Anomaly (MCA). The dynamics of pre-Columbian cultures from southwestern Amazonia seem to have been related to paleoclimatic and environmental changes reported for the region. • δ18O and δ13C speleothem records from lowland Amazon basin for late-Holocene. • Southwestern Amazonia present dry MCA and wet LIA periods documented by δ18O record. • Amazonia precipitation dipole due to enhanced SAMS activity reinforced by δ18O record. • Rainforest expansion over the last 3000 years documented by the δ13C record. [ABSTRACT FROM AUTHOR]