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The abrupt climate event Younger Dryas (YD) has been extensively studied; however, its structure is still poorly understood. Climate in northeastern Brazil is very sensitive to the latitudinal position of the intertropical convergence zone (ITCZ) associated with abrupt climate change in the Atlantic. Here, we report changes in the ITCZ position within the YD by using precise speleothem multiproxy records from northeastern Brazil. We provide evidence for a gradual northward migration of the ITCZ preceding poleward shifts of the westerlies and the polar front in northern high latitudes within the YD. This can be attributed to gradual increase in atmospheric CO2 concentration as a consequence of the weakening Atlantic Meridional Overturning Circulation (AMOC). We suggest that a persistent increase in atmospheric CO2 might have triggered a resumption of the AMOC and reorganization of the atmosphere circulation in the Atlantic during the mid‐YD. Plain Language Summary: The Younger Dryas (YD) is the most recent millennial‐scale abrupt climate event in Earth history. Although its origin has been extensively studied, its structure is still poorly understood. Climate in northeastern Brazil is very sensitive to the latitudinal position of the intertropical convergence zone (ITCZ) responds to abrupt climate change in the Atlantic (e.g., YD). By using stable isotope and trace element proxy records of speleothem from Toca da Boa Vista Cave, northeastern Brazil, together with other paleoclimatic records in the Atlantic realm, we provide evidence for a gradual northward migration of the ITCZ preceding poleward shifts of the westerlies and the polar front in northern high latitudes within the YD. This can be attributed to a gradual increase in atmospheric CO2 concentration under the situation of weakening Atlantic Meridional Overturning Circulation (AMOC). A persistent increase in atmospheric CO2 concentration might have triggered a resumption of the AMOC and reorganization of the atmosphere circulation in the Atlantic during the mid‐YD. Key Points: Speleothem and other paleoclimate records confirm a wet climate in tropical South America within the Younger DryasPrecise speleothem multiproxy records reflect a bipartition of the Younger Dryas precipitation in northeastern BrazilGradual South‐North climate transition in the Atlantic responded to a gradual increase in atmospheric CO2 within the YD [ABSTRACT FROM AUTHOR]

Due to the many factors controlling δ13C values in stalagmites, complicating their paleoclimatic and paleoenvironmental interpretation, most studies do not present δ13C values, but instead focus mainly on δ18O values. This is also the case for most cave studies from tropical South America, where many new δ18O stalagmite records covering the last millennia were recently published. Here, we test the influence of local hydroclimate, altitude, temperature and changing vegetation types on δ13C values in stalagmites, by employing a new dataset (named δ13C_2k_SA, https://doi.pangaea.de/10.1594/PANGAEA.919050) composed of published and unpublished carbon isotope records from various sites in tropical South America. Most locations were dominated by C3 plants over the last two millennia and are characterized by speleothem δ13C values more depleted than −6 ‰. The main factors influencing δ13C values are associated with the local hydroclimate, followed by minor effects from temperature. Most of the isotopic records show a significant correlation between the δ13C and δ18O values, indicating a close relationship between local hydroclimate and atmospheric convective processes related to the South American Monsoon System. [ABSTRACT FROM AUTHOR]

Locating suitable caves and stalagmites for palaeoenvironmental and palaeoclimatic studies can be challenging. Isotopic geochemical analyses, albeit commonly performed for palaeoclimatic reconstruction, are also time consuming and costly. Therefore, petrographic and non-destructive morphological studies on speleothems are desirable to facilitate sample selection for further analysis. In this study, 20 caves were surveyed in Ban Rai district, Uthai Thani province in western Thailand. After external physical observations in the field, three stalagmite samples were collected from Tham Nam Cave to test their potential for palaeoclimatic research. Firstly, the stalagmites were scanned by X-ray computed tomography ( CT scanning) and subsequently the CT images were compared with petrographic inspections. Columnar fabrics show the highest density, whereas closed and open dendritic fabrics have medium and the lowest densities, respectively. Layers near the top and bottom of the three stalagmites were dated by U-Th mass spectrometric techniques. All three samples were deposited between c. 87 and c. 105 ka ago; therefore, they are probably the oldest stalagmites that have been reported so far from mainland Southeast Asia. However, their physical features indicate that all the samples have suffered from postdepositional dissolution, and are unlikely to be suitable for palaeoclimatic research. The internal dissolution feature of stalagmites, however, cannot be identified by visual inspection of uncut samples. We hereby argue that CT images are useful to characterize stalagmite petrography, in particular fabric, porosity and density. Such features can be used to select the ideal plane of a stalagmite for sectioning, to maximize the chances of robust climatic reconstruction. [ABSTRACT FROM AUTHOR]

Abstract: Speleothem growth requires humid climates sufficiently warm to stimulate soil CO2 production by plants. We compile 283 U/Th dates on 21 stalagmites from six cave systems in the NW coast of Spain to evaluate if there are patterns in stalagmite growth that are evidence of climatic forcing. In the oldest stalagmites, from marine oxygen isotope stage (MIS) 7–5, growth persists through the glacial period. Hiatuses and major reductions in growth rate occur during extreme minima in summer insolation. Stalagmites active during the last interglaciation cease growth at the MIS 5–4 boundary (74ka), when regional sea-surface temperature cooled significantly. During MIS 3, only two stalagmites grew; rates were highest between 50 and 60ka during the maximum in summer insolation. One stalagmite grew briefly at 41ka, 36.5 and 28.6ka, all during warm phases of the Dansgaard–Oeschger cycles. A pronounced Holocene optimum in stalagmite growth occurs from 9 to 6ka. The cessation of most growth by 4.1ka, coincident with broad increases in aridity over the Mediterranean and areas influenced by the North African Monsoon, suggest that regions such as NW Spain, with dominant Atlantic moisture sources, also experienced increased aridity at this time. [Copyright &y& Elsevier]

The regional monsoons of the world have long been viewed as seasonal atmospheric circulation reversal-analogous to a thermally-driven land-sea breeze on a continental scale. This conventional view of monsoons is now being integrated at a global scale and accordingly, a new paradigm has emerged which considers regional monsoons to be manifestations of global-scale seasonal changes in response to overturning of atmospheric circulation in the tropics and subtropics, and henceforth, interactive components of a singular Global Monsoon (GM) system. The paleoclimate community, however, tends to view 'paleomonsoon' (PM), largely in terms of regional circulation phenomena. In the past decade, many high-quality speleothem oxygen isotope (δO) records have been established from the Asian Monsoon and the South American Monsoon regions that primarily reflect changes in the integrated intensities of monsoons on orbital-to-decadal timescales. With the emergence of these high-resolution and absolute-dated records from both sides of the Equator, it is now possible to test a concept of the 'Global-Paleo-Monsoon' (GPM) on a wide-range of timescales. Here we present a comprehensive synthesis of globally-distributed speleothem δO records and highlight three aspects of the GPM that are comparable to the modern GM: (1) the GPM intensity swings on different timescales; (2) their global extent; and (3) an anti-phased inter-hemispheric relationship between the Asian and South American monsoon systems on a wide range of timescales. [ABSTRACT FROM AUTHOR]

The tropics are the main source of the atmosphere's sensible and latent heat, and water vapour, and are therefore important for reconstructions of past climate. But long, accurately dated records of southern tropical palaeoclimate, which would allow the establishment of climatic connections to distant regions, have not been available. Here we present a 210,000-year (210-kyr) record of wet periods in tropical northeastern Brazil-a region that is currently semi-arid. The record is obtained from speleothems and travertine deposits that are accurately dated using the U/Th method. We find wet periods that are synchronous with periods of weak East Asian summer monsoons, cold periods in Greenland, Heinrich events in the North Atlantic and periods of decreased river runoff to the Cariaco basin. We infer that the wet periods may be explained with a southward displacement of the Intertropical Convergence Zone. This widespread synchroneity of climate anomalies suggests a relatively rapid global reorganization of the ocean-atmosphere system. We conclude that the wet periods probably affected rainforest distribution, as plant fossils show that forest expansion occurred during these intermittent wet intervals, and opened a forest corridor between the Amazonian and Atlantic rainforests. [ABSTRACT FROM AUTHOR]

Most precipitation records within the South American Summer Monsoon (SASM) domain bear a trend following the Southern Hemisphere summer insolation (SHSI). However, a growing number of past hydroclimate records have revealed a high degree of spatial variability in rainfall trends across tropical South America. Here we report a new speleothem δ18O record from central Brazil that underlies the South Atlantic Convergence Zone (SACZ). Our record reveals a nearly invariant rainfall trend over the mid-to-late Holocene, suggesting that the SACZ has maintained its latitudinal position and intensity despite the rising SHSI and consequently increasing monsoon strength in the core SASM zone. The record also shows no obvious response in SACZ rainfall to millennial-scale temperature anomalies in the North Atlantic. Instead, the long-term SACZ behaviour is likely dominantly influenced by subtropical South Atlantic sea surface temperatures, which can affect the position and intensity of moisture convergence over the continent. Our central Brazil speleothem record suggests that orbital-scale insolation change is not the dominant control of long-term SACZ rainfall trends. Alternative drivers of hydroclimate change need to be explored to account for regional differences in rainfall patterns within the SASM system. • SACZ rainfall remained insensitive to insolation change over the past 7000 years. • Mid-to-late Holocene North Atlantic events had minimal impact on core SACZ rainfall. • South Atlantic Ocean sea-surface temperatures significantly modulate the SACZ. [ABSTRACT FROM AUTHOR]

Abstract: Caves associated with doline slopes in the tectonically stable area of eastern Brazil display remarkable sequences of clastic sediment intercalated with calcite layers. Sediment erosion has also occurred allowing access to formerly sediment-filled passages. The palaeoenvironmental meaning and chronology of these three processes (i.e. clastic sediment input, clastic sediment erosion, and speleothem precipitation) were studied in both semi-arid Campo Formoso and sub-humid Lagoa Santa areas through 230Th dating and stratigraphical analyses. The dry climate of the Campo Formoso area prevents speleothem deposition at present, but soil erosion results in valley aggradation and cave infilling. Growth periods of speleothems and travertines in this area have allowed the recognition of recurrent past phases of increased humidity correlated with wet conditions recorded in southeastern Brazil speleothem calcite. At the Lagoa Santa area there is limited speleothem precipitation and sediment input at present. However, sediment entrainment is actively exhuming speleothems and exposing cave passages. Sediment erosion inside caves in the area is interpreted as being due to intermediate climatic conditions, not wet enough to favour speleothem deposition and not too dry to allow doline slope erosion and sediment transport into caves. Due to the low rates of denudation and isostatic rebound inherent to tectonically stable areas, cave passages will remain within the range of sediment infill and erosion for a much longer time than in tectonically active areas spanning, in average, at least three full glacial–interglacial cycles. As uplift proceeds, cave passages will be decoupled from the doline bottom and no longer will be affected by erosion or infilling episodes. Sediment filled passages in many caves in the Lagoa Santa region are relict features that display ancient clastic and chemical precipitation. The three processes described above have occurred throughout the life history of the caves, resulting in complex sediment assemblages that can, however, show significant intra- and inter-site variations. [Copyright &y& Elsevier]

Mainland Southeast Asia experiences complex and variable hydroclimatic conditions, mainly due to its location at the intersection of Asian monsoon subsystems. Predicting future changes requires an in-depth understanding of paleoclimatic conditions that is currently hindered by a paucity of records in some regions. In this paper, we present the first speleothem stable isotope records from western Thailand detailing the Bølling-Allerød interstadial, Younger Dryas termination, and early- to mid-Holocene period. We find evidence of higher precipitation during the Bølling-Allerød (14,321–12,824 years before present (1950: BP)) compared to a Younger Dryas termination that starts 11,702–11,674 BP, has a rapid shift centered on 11,660–11,641 BP, and ends 11,603–11,589 BP. In addition, our records show Holocene monsoon intensity peaking at 8250 BP or before, a multi-millennia delay from the Northern Hemisphere summer insolation peak, followed by a trend to drier conditions until at least 750 BP. Assessment of the timing of the Younger Dryas termination in paleoclimate records across Southeast Asia reveals an earlier shift of the Indian Summer Monsoon to global climate shifts when compared to East Asian Summer Monsoon records. The causes of this are currently unknown. Some potentially important aspects include: an Indian Summer Monsoon influence on East Asian Summer Monsoon strength via the Indian Ocean Dipole climate pattern, the role of the Tibetan Plateau in monsoon dynamics, and exposure of the Sundaland shoreline. More high-resolution paleoclimate records, especially on the pathway of Indian Summer Monsoon to East Asian Summer Monsoon, are required for further discussion on the mechanisms controlling the differences between climate regimes. • We present two new speleothem stable isotope records from western Thailand. • Conditions trend wetter during the Bølling-Allerød. • Early and abrupt termination of the Younger Dryas (11,675–11,600 BP, ±73 years). • Change Point Analysis of records finds earlier rapid shift in Indian Summer Monsoon. • Distinct trend of increasing δ18O and δ13C values throughout Holocene. [ABSTRACT FROM AUTHOR]

Abstract Investigating controls on past variability of South American hydroclimate is critical to assessing its response to future warming scenarios. δ18O records from South America offer insight into past variability of the South American Monsoon System (SAMS). The controls, however, on precipitation δ18O values can be decoupled from precipitation amount at a given site and, thereby, limit local moisture condition reconstructions. Here we use a principal components analysis to assess the coherence of speleothem and lake core Holocene δ18O records in tropical and subtropical South America to evaluate the extent to which δ18O variability reflects changes in SAMS intensity at different sites across the region. The main mode of variability across Holocene δ18O records (PC1) closely tracks austral summertime insolation, consistent with existing work. Sites towards the periphery of the continent are heavily weighted on PC1, whereas interior sites as not. Further δ18O variability at interior sites bear little similarity to each other and implicate controls, beyond regional monsoon intensity, on these δ18O records. Further, we develop speleothem 87Sr/86Sr records spanning the Holocene from Tamboril Cave (Brazilian Highlands), Paraíso Cave (eastern Amazon Basin), Jaraguá Cave (Mato Grosso do Sul Plateau), and Botuverá Cave (Atlantic coastal plain) to investigate coupling between reconstructed monsoon variability (reflected by PC1) and local moisture conditions (interpreted from 87Sr/86Sr records). We interpret speleothem 87Sr/86Sr variability as a proxy of local moisture conditions, reflecting the degree of water-rock interaction with the cave host rock as driven by variations in water residence time. Speleothem 87Sr/86Sr records from all the sites, except Botuverá cave, do not co-vary with PC1, suggesting that local moisture conditions do not necessarily follow variations in regional monsoon intensity at these interior sites. These speleothem 87Sr/86Sr records generally suggest dry mid-Holocene conditions relative to the early- and late-Holocene, consistent with interpretations of other paleo-moisture records in the region, but timing of wet-dry transitions varies between sites. These results highlight that controls, in addition to SAMS variability, might influence δ18O variability. Further, our results suggest spatially variable local moisture conditions at interior sites that do not uniformly respond to regional monsoon intensity, and stress the need for δ18O-independent reconstructions of moisture conditions. Highlights • The main mode of speleothem δ18O variability follows austral summertime insolation. • Speleothem 87Sr/86Sr values are a feasible proxy of local moisture conditions at our study sites. • Local moisture conditions are largely decoupled from overall monsoon intensity. • Speleothem 87Sr/86Sr values suggest a widespread mid-Holocene drying across study sites. [ABSTRACT FROM AUTHOR]

A Holocene stalagmite from Botuverá Cave, southeastern Brazil was analyzed by LA-ICPMS for Mg/Ca, Sr/Ca, Ba/Ca. The observed variability in the record was demonstrated to be modulated by prior calcite precipitation, and, thus, is interpreted to reflect monsoon intensity. We find that the calcite δ 18 O is strongly correlated with Sr/Ca, indicating that atmospheric circulation over South America and monsoon intensity have been tightly correlated throughout most of the Holocene, both directly responding to solar precession. Comparison with other contemporaneous high-resolution hydroclimate records reveals that SAMS has shown a degree of complexity during the Holocene not previously detected, with periods where the South American Convergence Zone (SACZ) expanded to cover most of the South American sub-continent, and coincident with periods of low-SST in the north Atlantic. We also detect periods where rainfall amount in northeastern and southeastern Brazil are markedly anti-phased, suggesting a north-south migration of SACZ, which it appears to be mediated by solar irradiance. The high-resolution nature of our record allow us to examine the effect that Holocene climate anomalies had upon SAMS dynamics and hydroclimate in southeastern Brazil, in particular the 8.2 ka event and the Little Ice Age. In addition to confirm the internal structure of the events, we also detect the possible consequences of the climatic anomalies upon ocean–atmosphere interactions through its effects upon SAMS. [ABSTRACT FROM AUTHOR]

Abstract: One of the most important developments in geomagnetism has been the recognition of polarity excursions of the Earth''s magnetic field. Accurate timing of the excursions is a key point for understanding the geodynamo process and for magnetostratigraphic correlation. One of the best-known excursions is the Blake geomagnetic episode, which occurred during marine isotope stage MIS 5, but its morphology and age remain controversial. Here we show, for the first time, the Blake excursion recorded in a stalagmite which was dated using the uranium-series disequilibrium techniques. The characteristic remanent magnetisation is carried by fine-grained magnetite. The event is documented by two reversed intervals (B1 and B2). The age of the event is estimated to be between 116.5±0.7kyr BP and 112.0±1.9kyr BP, slightly younger (∼3–4kyr) than recent estimations from sedimentary records dated by astronomical tuning. Low values of relative palaeointensity during the Blake episode are estimated, but a relative maximum in the palaeofield intensity coeval with the complete reversal during the B2 interval was observed. Duration of the Blake geomagnetic excursion is 4.5kyr, two times lower than single excursions and slightly higher than the estimated diffusion time for the inner core (∼3kyr). [Copyright &y& Elsevier]

Abstract: The geochronology and taphonomy of internationally important fossil bearing cave deposits were studied, both in the semi-arid Northern Bahia area and the subtropical southeastern Lagoa Santa area of Brazil. Taphonomic analysis suggests that the processes responsible for bone accumulation in the Brazilian caves vary between sites, and taphonomic bias can therefore be significant in causing differences in faunal composition. In the Toca da Boa Vista caves the presence of single articulated skeletons, and the entrance-related distribution indicate that random penetration of animals is the main mechanism of fossil accumulation, a process that biases the assemblage to smaller species, and takes place over extended time periods. In nearby Toca dos Ossos cave transport by runoff in the cave river is predominant, and biases the fauna remains to larger more robust bones and species. Deposition probably also occurred only at times of enhanced runoff giving a more contemporaneous assemblage. Similar processes were responsible for emplacement of the copious fossil remains in the more humid Lagoa Santa area, where terrigenous fossil deposits are found intercalated by massive speleothem calcite layers. In this area runoff under a drier climate probably accounts for the sediment emplacement inside caves. In both areas the mode of emplacement implies bias in the fossil record, resulting in fossil assemblages that do not mirror surface faunas, limiting palaeoenvironmental reconstruction. Mass spectrometric U-series analysis of speleothem calcite overlaying fossil remains gives minimum ages for fossil deposition. These ages confirm the previous view that many of the deposits derive from the late glacial, but also show that much older material (some >350,000 yr) is also present. The habitat requirements of critical fossil species such as bats and monkeys strongly suggest that they derive from much wetter periods when forest cover was present in the currently semi-arid Northern Bahia area. Taphonomy exerts a major control on the diversity and mode of emplacement of cave fossil deposits in eastern Brazil and thus detailed sedimentological and hydrological studies coupled with a sound geochronological approach are essential in quantifying the relative importance of each taphonomic processes before faunal and palaeoecological interpretations can be attempted. [Copyright &y& Elsevier]

Due to the many factors controlling δ13C values in stalagmites, complicating their paleoclimatic and paleoenvironmental interpretation, most studies do not present δ13C values, but instead focus mainly on δ18O values. This is also the case for most cave studies from tropical South America, where many new δ18O stalagmite records covering the last millennia were recently published. Here, we review the δ13C values in stalagmites, investigating the influence on this proxy of local hydroclimate, altitude, temperature and vegetation types, by employing a new dataset composed of published and unpublished carbon isotope records from various sites in tropical South America. The main factors influencing δ13C values are associated with the local hydroclimate, followed by minor effects from temperature. Most of the isotopic records show a significant correlation between the δ13C and δ18O values, indicating a close relationship between local hydroclimate and atmospheric convective processes related to the South American Monsoon System. • δ13C values in stalagmites from tropics are related with local hydrology. • Prior calcite precipitation is the main driver for δ13C values in stalagmites. • The mean conditions of local hydroclimate are associated with South American monsoon. • Dataset of δ13C values in stalagmites is useful as paleoclimate record. [ABSTRACT FROM AUTHOR]

Mainland Southeast Asia is located on the moisture transport route of the Indian summer monsoon (ISM) where hydroclimate records from speleothems have rarely been investigated. Here, we present a new multi-proxy (δ18O and δ13C values, trace element concentrations, and grayscale values) data set of stalagmite KPC1 from Khao Prae cave in western Thailand spanning the last 1400 years (500–1900 CE; the Common Era). These multi-proxy data reveal a high variability between the wet and dry periods during 500–850 CE and 1150–1300 CE, stable climate conditions during 850–1150 CE, and overall dry conditions since 1300 CE. The δ13C values, trace elements concentrations, and grayscale values show centennial-scale fluctuations, which were probably driven by local hydrological processes. In contrast, variations in the stalagmite δ18O values reflect integrated changes in rainfall amount from the ISM. The KPC1 record agrees with other speleothem δ18O records of Southeast Asian summer monsoon from the last millennium, as well as the lake multi-proxy and tree-ring PDSI data from Mainland Southeast Asia, but diverges from records from the Indo-Pacific equatorial regions and the western Pacific. We conclude that hydroclimate variability at the western side of Mainland Southeast Asia is mainly driven by changes in moisture transport of the ISM. On socially relevant timescales, the KPC1 data set shows that a period of stable rainfall (850–1150 CE) coincides with the early success of the early empires (e.g., Pagan, Angkor, and Dai Viet) in Mainland Southeast Asia. In line with previous studies in the region, we speculate that the high variability in rainfall between 1150 and 1300 CE and droughts during 1300–1550 CE played a significant role in the demise of ancient societies in Southeast Asia. • Stalagmite multi-proxy record of Thailand covering the last 1400 years. • Unstable conditions with long varying dry and wet phases during 500–850 CE and 1150–1300 CE. • Stable rainfall in 850–1150 CE and dry conditions since 1300 CE. [ABSTRACT FROM AUTHOR]

Karst area located in northwestern Vietnam is geologically well-known as a tectonically extruded block apart from its counterpart: Permian limestone distributed in Yunnan, southern China. It has long been geographically stabilized since its early sinistral movement ceased in middle Miocene. Its distribution covers latitudes roughly from 21 to 23 degree north where is currently located within the summer ITCZ. Enormous karst caves are formed due to the sufficient groundwater replenishment and speleothems are consequently developed including stalactite or stalagmite. With the purpose of understanding the paleo-precipitation changes in respond to the evolution of the global climate change, we collected stalagmites and used geochemical analyses to conduct sequential isotopic values and corresponding ages. Two of them within the age range from 22ka to 33ka display continuous records of precipitation in this period. Global climate events: the Heinrich events II, III and Dansgaard-Oeschger events 3 and 4 can be recognized in our records, similar to other speleothems collected in low latitudes. However, the changing patterns including starting time, rate, and duration are different from place to place when comparing with other geographical records. Also, our high-resolution results obviously exhibit centennial-scale events. According to the previous studies the Oxygen isotope record of speleothem is mainly controlled by the precipitation changes in this latitude. We believe those explicit features found in northwestern Vietnam are related to the strength variation of Asia Summer Monsoon, which is governed by the global climate forcing in both scales of millennium and centennial. [ABSTRACT FROM AUTHOR]