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Fungal studies are scant within this region of Borneo, and the potential effects of anthropogenic disturbance on fungal communities in Sabahan caves have not been explored. This study involved opportunistic sampling of guano, speleothems, and cavern water from four caves in Sabah, Malaysia, categorised according to the level of anthropogenic activity. The dilution method was used for fungal isolation and abundance calculations. Morphological identification of axenic cultures was conducted, and DNA barcoding of the ITS region of cryptic species corroborated identification. A total of 170 axenic cultures were attained, composed of 69 morphological taxonomic units (MTUs), 33 genera, ten orders, and two divisions -- Ascomycota and Basidiomycota. Fifty-seven of the 69 MTUs were identified to the species level. The genera Aspergillus and Penicillium were particularly prevalent, with a combined total of 86 isolations (50.6%). Notably, twelve species were documented for the first time in cave ecosystems of Sabah. The average fungal abundance across all substrates and fungal taxa occurrence was found to be higher in samples found in active caves. A significant difference in relative abundance was observed between active and non-active cave conditions. Beta regression modelling indicated that anthropogenic activity is a significant factor influencing the composition of cave fungal communities. While anthropogenic activity seems to affect cave mycobiomes, especially by selecting for ubiquitous fungi, it is likely not the sole influencing determinant of their composition. [ABSTRACT FROM AUTHOR]

This study investigates the dissolution characteristics of a stalactite from Küpeli Cave in southern Turkey, employing a holistic approach that includes macroscopic and microscopic analyses alongside advanced techniques such as X-ray diffraction, and scanning electron microscopy. The studied stalactite exhibits distinct morphological features: an upper main body with visible growth layers and dissolution channels, and a lower pendant made of solid sparite calcite crystals. The outer surface of the main body exhibits partial dissolution corrosion and protrusion-like structures resulting from channel infilling resisting corrosion. Notably, the pendant section of the stalactite remains largely unaffected by the dissolution, preserving its original structure. The longitudinal cross-section of the main body reveals dissolution channels along the growth layer's surface, partially filled with calcite cement. Secondary channels branch off the main channels, some connected to the outer surface at certain points, allowing cave water to enter. The dissolution processes also lead to microscale changes in the primary microfabrics, including the widening of intercrystalline pores, microperforated zones, microchannels, rhombohedral microcrystalline blocks, spiky calcite, pits, and abiotic micritization. The recurring dissolution features inside the stalactite indicate synchronous dissolution during stalactite formation, where the precipitation/dissolution conditions repeat cyclically. Dissolution typically occurs during the rainy season when cave water is unsaturated with calcite, otherwise, calcite precipitates, forming overgrowth layers and/or cement. [ABSTRACT FROM AUTHOR]

The regional impact of abrupt glacial climate variability remains poorly constrained for arid southwestern Asia, particularly winter dynamics during Marine Isotope Stage 3, due to limited paleoarchives in the Middle East. Here, we present continuous speleothem records of δ18O and δ13C with robust chronologies for southwestern and central Iran, spanning ∼50–30 ka. Stable‐isotope signals in the two stalagmites are generally uncorrelated and do not exhibit a consistent response to Greenland stadials or interstadials; however, both show a positive δ18O excursion that coincides with Heinrich event 4. We explore the potential mechanisms for intermittent coupling of speleothem δ18O across Iran through isotope‐enabled atmospheric modeling outputs, from which we utilize the spatial δ18O gradient as a proxy for wintertime westerly versus southerly jet strength. Our results suggest that during Heinrich event 4 and several Greenland stadials, stronger westerly winds enhanced Mediterranean moisture contributions to both sites and reduced aridity in southern Iran. Plain Language Summary: Stalagmites are useful archives to reconstruct the climate of the past. In order to shed light on the past climate of western Asia and the response of this region to the rapid climate changes, here we present two stalagmites from central and southwestern Iran that span 50,000 to 30,000 yrs ago. Our findings suggest that during extreme cold events, the moisture originates mostly from the west, whereas out of these extraordinarily cold periods moisture comes mostly from the south. Key Points: Continuous high‐resolution speleothem record of climatic change in southwestern and central Iran between 50 and 30 kaDecoupled responses of stable‐isotope gradients in central and southern Iran to glacial climate variability, except during Heinrich event 4Decreased impact of southerly moisture sources and reinforced westerlies during extreme cold events [ABSTRACT FROM AUTHOR]

We present a continuous high-resolution precisely dated multiproxy record of hydroclimate variability at Anjohibe cave in northwestern Madagascar using speleothem AB13. The record spans from ~4484 y BP to ~2863 y BP. Stalagmite δ18O, δ13C and Sr/Ca ratios show very similar changes in hydroclimate. The mechanism controlling Sr/Ca changes, however, from prior calcite precipitation to degree of dolomite dissolution at about 4 ky BP. Our record is also in good agreement with previously published speleothem records from the same area. This agreement and multiproxy consensus indicate that AB13 provides a robust record of hydroclimate variability, including a continuous record of hydroclimate variability across the 4.2 ka event. This 4.2 ka event in Madagascar is marked by two distinct periods of drying between ~3900 y BP to 4300 y BP. A dry 4.2 ka event at this Southern Hemisphere site helps limit possible mechanisms for the event, indicating that a meridional shift to the south in the ITCZ is not responsible for the 4.2 ka event. In addition, the 4.2 ka event does not stand out as a unique dry period in our record. The longest and driest period of the record lasted ~300 years with peak dryness at ~3000 y BP. Our record differs significantly from a speleothem record from Rodrigues Island, located ~1800 km to the east of our study area in Madagascar suggesting different climatological controls on northwest Madagascar and more oceanic sites to the east. [ABSTRACT FROM AUTHOR]

The Indo-Pacific, a vast biogeographic of Earth, is influenced by both the Indian and East Asian monsoons. Despite its geographical importance, this region has been less studied compared to East Asia and India. Here, we present speleothem records from southern Thailand that cover the last 1500 years, including a hiatus during the Little Ice Age, providing insights into the interactions among climate dynamics, human influences, and ecological responses to climate change. Notably, our records lack the characteristic cold and warm periods observed in other regions, such as the Dark Ages Cold Period and Medieval Warm Period, which may reflect the complexity of the tropical climate system or the region's unique topography. The analysis reveals a link between ENSO multi-decadal variability and hydroclimate conditions in southern Thailand, as evidenced by speleothem δ18O. Furthermore, a comparison between speleothem δ13C and the Normalized Difference Vegetation Index (NDVI) indicates significant vegetation changes in the last three decades, corresponding with increased atmospheric CO2 levels and expansion of agricultural land due to human activities during the Current Warm Period. Additionally, our study suggests that an abrupt increase in sea surface temperatures may enhance vegetation growth in the Indo-Pacific by influencing atmospheric circulation and increasing precipitation. [ABSTRACT FROM AUTHOR]

Background: Moonmilk represents complex secondary structures and model systems to investigate the interaction between microorganisms and carbonatic rocks. Grotta Nera is characterized by numerous moonmilk speleothems of exceptional size hanging from the ceiling, reaching over two meters in length. In this work we combined microbiological analyses with analytical pyrolysis and carbon stable isotope data to determine the molecular composition of these complex moonmilk structures as well as the composition of the associated microbiota. Results: Three moonmilk structures were dissected into the apical, lateral, and core parts, which shared similar values of microbial abundance, richness, and carbon isotopes but different water content, microbiota composition, and organic matter. Moonmilk parts/niches showed higher values of microbial biomass and biodiversity compared to the bedrock (not showing moonmilk development signs) and the waters (collected below dripping moonmilk), indicating the presence of more complex microbial communities linked to carbonate rock interactions and biomineralization processes. Although each moonmilk niche was characterized by a specific microbiota as well as a distinct organic carbon profile, statistical analyses clustered the samples in two main groups, one including the moonmilk lateral part and the bedrock and the other including the core and apical parts of the speleothem. The organic matter profile of both these groups showed two well-differentiated organic carbon groups, one from cave microbial activity and the other from the leaching of vascular plant litter above the cave. Correlation between organic matter composition and microbial taxa in the different moonmilk niches were found, linking the presence of condensed organic compounds in the apical part with the orders Nitrospirales and Nitrosopumilales, while different taxa were correlated with aromatic, lignin, and polysaccharides in the moonmilk core. These findings are in line with the metabolic potential of these microbial taxa suggesting how the molecular composition of the preserved organic matter drives the microbiota colonizing the different moonmilk niches. Furthermore, distinct bacterial and archaeal taxa known to be involved in the metabolism of inorganic nitrogen and C1 gases (CO2 and CH4) (Nitrospira, Nitrosopumilaceae, Nitrosomonadaceae, Nitrosococcaceae, and novel taxa of Methylomirabilota and Methanomassiliicoccales) were enriched in the core and apical parts of the moonmilk, probably in association with their contribution to biogeochemical cycles in Grotta Nera ecosystem and moonmilk development. Conclusions: The moonmilk deposits can be divided into diverse niches following oxygen and water gradients, which are characterized by specific microbial taxa and organic matter composition originating from microbial activities or deriving from soil and vegetation above the cave. The metabolic capacities allowing the biodegradation of complex polymers from the vegetation above the cave and the use of inorganic nitrogen and atmospheric gases might have fueled the development of complex microbial communities that, by interacting with the carbonatic rock, led to the formation of these massive moonmilk speleothems in Grotta Nera. [ABSTRACT FROM AUTHOR]

We present a 500‐year precipitation‐sensitive record based on co‐varying speleothem δ18O values and Mg/Ca ratios from Larga cave in Puerto Rico. This multi‐proxy record shows that the evolution of rainfall in the northeastern Caribbean was characterized by alternating centennial dry and wet phases corresponding to reduced versus enhanced convective activity. These phases occurred synchronous with relatively cool and warm tropical Atlantic sea‐surface temperatures (SSTs), respectively. While the observed pattern suggests a close link of northeastern Caribbean rainfall to the Atlantic Multidecadal Variability, a regional comparison reveals intermittent regional heterogeneity especially on decadal timescales, which may be related to a superimposing influence of the Pacific and Atlantic basins. Furthermore, the speleothem‐based hydroclimate reconstruction indicates a significant volcanic impact during the past two centuries, and further reveals a potential solar signal in the preceding three centuries. We posit that the forcing likely shifted from solar to volcanic during the eighteenth century in being an important source of multidecadal to centennial Caribbean rainfall variability. The link between convective rainfall and natural forcing may be explained through a modulation of SST variations in the tropical Atlantic and Pacific oceans. Plain Language Summary: Climate change is expected to affect rainfall throughout the Caribbean and Central America, where over 200 million people are heavily dependent upon rain as their main source of freshwater. We have looked at how the amount of rainfall in the Caribbean has changed through time, and possible reasons for these changes, to inform predictions of future rainfall patterns for the region. Cave mineral deposits, also known as speleothems, can be used to assess the amount of regional rainfall in the past by looking at their slight changes over time in the mineral's chemical composition. We created a record of Caribbean rainfall spanning the last five centuries using a speleothem from Puerto Rico. Our results indicate that rainfall changes since the sixteenth century were strongly influenced by changes in temperatures of the surface waters of the Atlantic Ocean. We further found that changes in the sun's brightness and volcanic eruptions may alter Atlantic Ocean sea‐surface temperature, which in turn affect the overall changes in Caribbean rainfall patterns. Key Points: Speleothem‐based Puerto Rican rainfall reconstruction shows prominent multidecadal‐to‐centennial variability during the past five centuriesPuerto Rican rainfall fluctuations are linked to solar variations before the eighteenth century and volcanic forcing thereafterCaribbean Sea‐surface temperature anomalies as part of the Atlantic Multidecadal Variability emerge as robust precursor of rainfall amounts [ABSTRACT FROM AUTHOR]

The timing and geographic extent of a potential "4.2 ky event" remain highly contested. Here we present records of ENSO variability at 3.8 kyBP and 4.1 kyBP derived from a Borneo stalagmite, which suggest a significant change in ENSO properties between these time intervals. The Borneo records show evidence of significantly reduced ENSO activity at 4.1 kyBP, relative to other measured windows within the Holocene. This reduced ENSO activity coincides with a period of drier conditions and enhanced dust events in the Middle East that took place ∼4.0–4.3 kyBP. The Borneo records show evidence of enhanced ENSO activity at 3.8 kyBP. Various hydroclimate changes attributed to the "4.2 ky event" in many regions may thus be reflecting a shift from reduced to enhanced El Niño activity that occurred between 3.8 kyBP to 4.0 kyBP. Plain Language Summary: Research suggests that a significant climate shift may have occurred around 4,000 years ago, though the exact timing and global extent of the event remain uncertain. A change in the frequency or magnitude of the El Niño‐Southern Oscillation (ENSO) is one hypothesized cause, however there are currently few high‐resolution records which resolve ENSO variability 4,000 years ago. We present a new western tropical Pacific stalagmite‐based record of ENSO activity, which shows a significant minimum in ENSO variability around 4,100 years ago. This reduced ENSO activity coincides with a centennial‐scale climate event in the Middle East characterized by drier conditions and enhanced dust events. The Borneo record also shows a significant increase in El Niño/La Niña activity that took place by 3,800 years ago. Hydroclimate changes around 4,000 years ago found in records from multiple regions around the world may therefore reflect a shift from reduced to enhanced El Niño activity. Key Points: Borneo stalagmite record shows anomalously low El Niño‐Southern Oscillation variability in a 135‐year‐long window, centered at 4.1 kyBPBorneo stalagmite record suggests an abrupt shift from low to high El Niño‐Southern Oscillation variability between 3.8 and 4.0 kyBPRecords of tropical hydroclimate change ∼4,000 years ago may reflect a significant increase in El Niño variability [ABSTRACT FROM AUTHOR]

A speleothem collected from Palco Cave (Puerto Rico) spans the 8.2 ka event, a time interval associated with fluctuations of Atlantic Ocean circulation and possible drying in the Caribbean region. While stalagmite δ18O, δ13C, and Mg/Ca data do not show a sustained change in mean state over the 8.2 ka event, the proxies provide robust evidence for three abrupt fluctuations toward drier conditions in rapid succession, each lasting less than two decades, occurring at 8.20, 8.14, and 8.02 ka BP. A cave monitoring program at Palco Cave supports the interpretation of the speleothem proxy records. Because changes in the position of the Intertropical Convergence Zone (ITCZ) are directly coupled to sea-surface temperature variations in the North Atlantic, we hypothesize that cold events in the North Atlantic temporarily limited the northward migration of the ITCZ and tropical rain belt in boreal summer during these abrupt drying periods. The speleothem record suggests that the 8.2 ka event was associated with rapid rainfall fluctuations in the northern Caribbean followed by a comparably warm and wet phase after the 8.2 ka event. This enhanced variability during the transitional period of the deglaciation appears to be linked to a fast coupling between interacting oceanic and atmospheric processes. This involves, in particular, the Atlantic Meridional Overturning Circulation in modulating interhemispheric heat transport. [ABSTRACT FROM AUTHOR]

Recent research has shown the potential of speleothem δ13C to record a range of environmental processes. Here, we report on 230Th-dated stalagmite δ13C records for southwest Sulawesi, Indonesia, over the last 40,000 yr to investigate the relationship between tropical vegetation productivity and atmospheric methane concentrations. We demonstrate that the Sulawesi stalagmite δ13C record is driven by changes in vegetation productivity and soil respiration and explore the link between soil respiration and tropical methane emissions using HadCM3 and the Sheffield Dynamic Global Vegetation Model. The model indicates that changes in soil respiration are primarily driven by changes in temperature and CO2, in line with our interpretation of stalagmite δ13C. In turn, modelled methane emissions are driven by soil respiration, providing a mechanism that links methane to stalagmite δ13C. This relationship is particularly strong during the last glaciation, indicating a key role for the tropics in controlling atmospheric methane when emissions from high-latitude boreal wetlands were suppressed. With further investigation, the link between δ13C in stalagmites and tropical methane could provide a low-latitude proxy complementary to polar ice core records to improve our understanding of the glacial–interglacial methane budget. [ABSTRACT FROM AUTHOR]

Speleothem fluorescence can provide insights into past vegetation dynamics and stalagmite chronology. However, its origin and especially the formation of fluorescent laminations in stalagmites are poorly understood. We conducted a year-long monthly monitoring of drip water fluorescence in La Vallina Cave (northern Iberian Peninsula) and compared the results to drip water chemistry and active speleothems from the same sites. Drip waters were analyzed using fluorescence spectroscopy and parallel factor analysis (PARAFAC). The resulting five-component model indicates contributions from vegetation, microbial activity, and bedrock. Intra-site fluorescence variability is mainly influenced by changes in overlying vegetation, water reservoir time, and respiration rates. Contrary to prevailing views, we find no systematic increase in drip water fluorescence during rainy conditions across drip sites and seasonal variations in drip water fluorescence are absent at a location where present-day speleothem layers form. Our findings challenge the notion of a higher abundance of humic-like fluorescence during the rainy season as the primary cause for layer formation and suggest additional controls on drip water fluorescence, such as bedrock interaction and microbial reprocessing. We also propose that growth rate may control the dilation of the fluorescence signal in stalagmites, indicating other potential mechanisms for fluorescent layer formation. [ABSTRACT FROM AUTHOR]

This study presents the results of a detailed paleoclimate investigation on stalagmite YL-1 (Yelini Cave, Türkiye). YL-1 grew between 117.13 (+0.57/−0.44) ka and 114.87 (+1.63/−2.89) ka within Greenland Stadial 26, indicating a positive moisture balance during the stadial conditions in this semi-arid region. Rainfall is significantly affected by sub-cloud and surface evaporation and decreasing net effective winter precipitation is recorded by high isotope values. Enriched δ18O and δ13C at 116.65 (+0.51/−0.39) ka are interpreted as a drought event that took place ca. 400 years before the end of the MIS 5e. This event, which was reported simultaneously in marine and terrestrial archives in the Northern Hemisphere, is a result of decreased cyclone activity linked to weakening of the Atlantic meridional overturning circulation. 87Sr/86Sr values of YL-1 are close to the host-rock values. Decreased 87Sr/86Sr ratio at 116.67 (+0.54/−0.38) ka reflects the intensified water–rock interaction due to lower precipitation. Along with prior calcite precipitation effect, this is also observed by increased Mg/Ca and Sr/Ca, while low P, Cu, Be, Y, and Zr concentrations indicate a lowered amount of soil-derived colloidal material. The MIS 5e/5d transition is marked by reduced insolation and enriched δ18O at 116.24 (+0.53/−0.86) ka. The Greenland Interstadial 25 phase at 115.87 (+0.83/−1.71) ka is represented by more negative δ18O and δ13C. [ABSTRACT FROM AUTHOR]

This study utilizes speleothem trace elements as climate proxies to reconstruct hydroclimate variability over approximately 350 years in the Southern Cook Islands. Stalagmites Pu17 and Pu4 from Pouatea cave were analyzed using high-resolution LA-ICP-MS for trace elements (Mg, Na, Sr, P, U, Y). By monitoring cave dripwater and conducting regression analysis, we found that Mg, Sr, and Na in Pouatea dripwater mostly originated from marine aerosols, while Sr and Ba were primarily from bedrock, with additional Ba coming from marine aerosols and weathered oceanic basalt leaching. Mg was identified as the most reliable element for hydroclimate reconstruction due to its predominantly marine aerosol origin. Infiltration, via dilution of marine aerosols and bedrock inputs, was identified as the main driver of trace element variations in Pouatea at a seasonal scale. Transfer functions were established between each trace element and effective infiltration was calculated, with Mg showing the strongest correlation. The reconstructed infiltration data were compared with climate indices, showing an overarching role of the SPCZ and ENSO in controlling rainfall in the South Pacific. This research demonstrates the potential of speleothem trace elements for paleohydroclimate reconstructions, improving understanding of rainfall variability in the climatically vulnerable South Pacific Islands over the past millennia. [ABSTRACT FROM AUTHOR]

A stalagmite was collected in northern Hungary from the Vacska Cave, where monitoring and ventilation-based site selection had been conducted. The stalagmite covers the 10–8 ka (relative to AD 1950) period, including the so-called 8.2 ka event, and showed preceding signs of climate change that were evaluated by petrographic observations, 14C activities, Sr concentrations, and stable isotope compositions of calcite and inclusion-hosted water. Comparisons of speleothem records show that isotope peaks at ca. 8.5 ka are related to a regional climate anomaly, rather than to a continental-scale event. In accordance with regional proxy records, the 8.2 ka event was associated with a series of temperature and precipitation amount changes, starting with cooling and a reduction in the winter-to-summer precipitation ratio, and then becoming a humid and warm phase at 8.15 ka. X-ray diffraction-based crystallinity parameter (FWHM) values provided evidence for diagenetic alteration of the stable oxygen isotope compositions of inclusion waters. Nevertheless, the stable hydrogen isotope compositions of inclusion waters and the oxygen isotope values of the host calcite revealed elevated d-excess values, and therefore increased Mediterranean moisture contribution during the 8.2 ka event, which indirectly indicate the southward displacement of moisture transport from the Atlantic Ocean. [ABSTRACT FROM AUTHOR]

Pollen preserved in caves provides a little-appreciated opportunity to study past vegetation and climate changes in regions where conventional wetland sediments are either unavailable, contain little organic matter, and/or are difficult to date accurately. Most palynology in caves has focused on clastic infill sediments, but pollen preserved in growing speleothems provides important new opportunities to develop vegetation and climatic records that can be dated accurately with radiometric methods. However, when pollen is present in speleothems, concentrations can vary by orders of magnitude, highlighting how little we know about the processes that transport pollen into caves and onto speleothem surfaces, and that determine the pollen's preservation probability. To explore these aspects of speleothem pollen taphonomy, we investigated the distribution of pollen and microscopic charcoal within several stalagmites from southwest Australia. We examined spatial patterns in pollen and charcoal preservation in order to distinguish whether observed gradients result from preservation or are products of systematic transport processes working along stalagmite surfaces. We find that pollen grains and charcoal fragments are located preferentially on the flanks of most stalagmites. This suggests that pollen grain and charcoal deposition on speleothems is influenced by transport and accumulation of detrital debris on growing surfaces. These insights will assist in future sampling campaigns focusing on speleothem pollen and charcoal contents. [ABSTRACT FROM AUTHOR]

The 8.2 ka event is the most significant global climate anomaly of the Holocene epoch, but a lack of records from Mainland Southeast Asia (MSEA) currently limits our understanding of the spatial and temporal extent of the climate response. A newly developed speleothem record from Tham Doun Mai Cave, Northern Laos provides the first high‐resolution record of this event in MSEA. Our multiproxy record (δ18O, δ13C, Mg/Ca, Sr/Ca, and petrographic data), anchored in time by 9 U‐Th ages, reveals a significant reduction in local rainfall amount and weakening of the monsoon at the event onset at ∼8.29 ± 0.03 ka BP. This response lasts for a minimum of ∼170 years, similar to event length estimates from other speleothem δ18O monsoon records. Interestingly, however, our δ13C and Mg/Ca data, proxies for local hydrology, show that abrupt changes to local rainfall amounts began decades earlier (∼70 years) than registered in the δ18O. Moreover, the δ13C and Mg/Ca also show that reductions in rainfall continued for at least ∼200 years longer than the weakening of the monsoon inferred from the δ18O. Our interpretations suggest that drier conditions brought on by the 8.2 ka event in MSEA were felt beyond the temporal boundaries defined by δ18O‐inferred monsoon intensity, and an initial wet period (or precursor event) may have preceded the local drying. Most existing Asian Monsoon proxy records of the 8.2 ka event may lack the resolution and/or multiproxy information necessary to establish local and regional hydrological sensitivity to abrupt climate change. Plain Language Summary: The most significant global climate event in the last ∼11,000 years occurred ∼8,200 years ago (the "8.2 ka event"). Many globally distributed records of past climate (paleoclimate) document significant changes during the event, but there are few from Mainland Southeast Asia available to reconstruct the climate impacts in this region. We present a new speleothem (cave sample) record from Tham Doun Mai Cave, Northern Laos that uses multiple geochemical and physical signals (proxies) to document local and regional climate effects of the 8.2 ka event at a high resolution. Using oxygen isotopes, we find that the 8.2 ka event weakened regional monsoon intensity for at least ∼170 years, which resembles findings from other studies. However, other proxies suggest local rainfall changed abruptly decades before the signal of monsoon weakening. Additionally, local drying may have lasted much longer than current estimates of 8.2 ka event responses. Most proxy records of the 8.2 ka event in monsoon regions lack similar multiproxy information and/or do not have high enough resolution to fully capture the climatic response. Additional records like ours from monsoon regions may assist in establishing how sensitive local and regional rainfall is to abrupt climate change. Key Points: High‐resolution speleothem record of the 8.2 ka event in northern Laos shows weakened monsoon intensity and reduced local rainfall amountsMultiproxy data suggest the disruption to local rainfall amounts started decades before the weakened monsoon intensity inferred from δ18OPrevious monsoon records of the event lack the resolution and/or multiproxy dimensions needed to reconstruct local hydrologic changes [ABSTRACT FROM AUTHOR]

Ice core records from Greenland provide evidence for multiple abrupt cold–warm– cold events recurring at millennial time scales during the last glacial interval. Although climate variations resembling Dansgaard–Oeschger (DO) oscillations have been identified in climate archives across the globe, our understanding of the climate and ecosystem impacts of the Greenland warming events in lower latitudes remains incomplete. Here, we investigate the influence of DO-cold-to-warm transitions on the global atmospheric circulation pattern. We comprehensively analyze δ18O changes during DO transitions in a globally distributed dataset of speleothems and set those in context with simulations of a comprehensive high-resolution climate model featuring internal millennial-scale variations of similar magnitude. Across the globe, speleothem δ18O signals and model results indicate consistent large-scale changes in precipitation amount, moisture source, or seasonality of precipitation associated with the DO transitions, in agreement with northward shifts of the Hadley circulation. Furthermore, we identify a decreasing trend in the amplitude of DO transitions with increasing distances from the North Atlantic region. This provides quantitative observational evidence for previous suggestions of the North Atlantic region being the focal point for these archetypes of past abrupt climate changes. [ABSTRACT FROM AUTHOR]

The central part of the Western Desert of Egypt, where the Bahariya and Farafra oases are situated, possesses many notable geological features. However, to date the related geoheritage information remains incomplete. Field investigation has permitted the characterization of ten localities representing Quaternary environments, which were rather humid and, thus, differed from the present hyper-arid conditions. Lacustrine-palustrine calcretes and dolocretes, lake (playa) deposits, fluvial tufa and travertines, speleothems (cavern deposits), and aeolian nebkha facies are among the features of these localities. Tentatively, a geosite with a new form is proposed for the studied entity of the localities, namely a serial geosite; this term signifies geosites embracing localities representing the same geological phenomenon, but scattered in the study area. The managerial implications of this study are recommendations for careful planning based on the geosite descriptions. [ABSTRACT FROM AUTHOR]

Most paleoclimate studies of Mainland Southeast Asia hydroclimate focus on the summer monsoon, with few studies investigating rainfall in other seasons. Here, we present a multiproxy stalagmite record (45,000 to 4,000 years) from central Vietnam, a region that receives most of its annual rainfall in autumn (September- November). We find evidence of a prolonged dry period spanning the last glacial maximum that is punctuated by an abrupt shift to wetter conditions during the deglaciation at ~14 ka. Paired with climate model simulations, we show that sea- level change drives autumn monsoon rainfall variability on glacial- orbital timescales. Consistent with the dry signal in the stalagmite record, climate model simulations reveal that lower glacial sea level exposes land in the Gulf of Tonkin and along the South China Shelf, reducing convection and moisture delivery to central Vietnam. When sea level rises and these landmasses flood at ~14 ka, moisture delivery to central Vietnam increases, causing an abrupt shift from dry to wet conditions. On millennial timescales, we find signatures of well- known Heinrich Stadials (HS) (dry conditions) and Dansgaard--Oeschger Events (wet conditions). Model simulations show that during the dry HS, changes in sea surface temperature related to meltwater forcing cause the formation of an anomalous anticyclone in the Western Pacific, which advects dry air across central Vietnam, decreasing autumn rainfall. Notably, sea level modulates the magnitude of millennial- scale dry and wet phases by muting dry events and enhancing wet events during periods of low sea level, highlighting the importance of this mechanism to autumn monsoon variability. [ABSTRACT FROM AUTHOR]

Aim: The geography and genesis of diversity remain an enduring topic in ecology and evolution. Mediterranean Climate Ecosystems (MCEs), with their high plant diversities in winter rainfall climates, pose a challenge to popular hypotheses evoking high water availability and temperature as necessary for the evolution of high diversity. We test the hypothesis of environmental stability as a driver for the evolution of regional‐scale floristic diversity using speleothem oxygen (δ18O) and carbon (δ13C) isotopic values as proxies for past climatic variability in the Cape Floristic Region (CFR) and other MCEs. Location: south‐western Africa, California, Mediterranean Basin. Taxon: Plantae. Methods: We present new speleothem δ18O and δ13C records from a cave near Robertson in the western CFR. Stable isotope samples included in the analyses cover the time intervals between 240 and 670 ka BP with hiatuses at 630–500 ka and 360–310 ka. The dispersion of these stable isotope records is used as a measure for climatic variability. We compare our new analyses to speleothem records that cover full glacial and interglacial conditions in other MCEs (California and the Mediterranean Basin) as well as in eastern regions of the CFR. All sites used in this comparison have lower vascular plant biodiversity than the western CFR. Results: Analyses of the dispersion of the δ18O and δ13C datasets suggest that the highly diverse western CFR experienced climatic stability across several glacial–interglacial cycles, compared with the less diverse regions within and outside of the CFR. Main Conclusion: This result provides support for the hypothesis that lower extinction rates associated with Pleistocene biome stability may explain the higher diversity in the CFR relative to other MCEs. [ABSTRACT FROM AUTHOR]

Calc tufas are terrestrial, cold water precipitation deposits commonly formed in semi-arid to temperate climates from saturated waters due to carbon dioxide degassing, microbial processes or both. Several calc tufa sites occur along rapids and waterfalls in the upland plateau of the Deccan Traps in western India. Small deposits occur along the Harishchandragad ranges (Bhramanwada, Kotul), Kanhur plateau (Ane Ghat, Wadgaon Darya and Vambori) and the Sinhagad-Bhuleshwar Ranges (Katraj, Shindone, Ambale and Bhuleshwar) in the upland regions of western Deccan Traps. Calc tufa is porous and friable covered with dry organic debris, with encrusted stems, trunk and calcified roots representing phytoherm framestone facies. Well-developed clusters of stalactites are exposed on the roof of a cavern or along cascades. Mineralogically, the calc tufas are made of calcite and contain variable carbonate percentages (53 to 78%) with detrital basalt fragments, devitrified glass, plagioclase, quartz, agate, zeolites etc. The calc tufa from the study area shows δ18OV-SMOW values ranging from 25.3 to 28.9‰ and δ13CV-PDB values from − 3.6 to − 9.42‰ indicating significant regional variation in precipitation and source characteristics. The calc tufas were biological and physicochemically precipitated from waters at paleo temperatures of 16.3 to 27.1 °C (Kotul-Ane Ghat) and 29.5 to 34.6 °C (Bhuleshwar Ghat-Wadgaon Darya) in temperate to semi-arid climate. Despite their hydrogeological significance and importance as paleoclimatic indicators, the calc tufa occurrences from upland Deccan Traps have not received the attention they deserve. The calc tufa sites at Kotul, Wadgaon Darya and Vambori have very high (> 6.5) scientific values. The sites of Wadgaon Darya (6.75) and Vambori (8.8) have very high didactic value (VD) while most sites have high to very high touristic or recreational value (VT ~ 6 to 7.3). The high to very high assessment of the anthropogenic risk of degradation to some sites from this study calls for the preservation and conservation of these important geoheritage sites. [ABSTRACT FROM AUTHOR]

Cave carbonates, seemingly growing in defiance of gravity, have attracted the community's interest for more than a century. This paper focusses on 'helictites', contorted vermiform speleothems with central capillaries. Petrographic, crystallographic and geochemical data of calcitic and aragonitic helictites (recent to 347 ka) from three caves in Western Germany are placed in context with previous work. Aragonitic helictites from one site, the Windloch Cave, form exceptionally large and complex structures that share similarities with the celebrated helictite arrays in the Asperge Cave in France. Aragonitic and calcitic helictites differ significantly in their crystal fabrics and internal geometry. Calcitic helictites are best described as a composite crystal fabric consisting of fibrous mesocrystals. Aragonite helictites display a complex fabric of acicular to platy crystals, some of which show evidence for growth‐twinning and perhaps crystallisation via a monoclinal precursor stage. The micro‐tomographic characterisation of several orders of channels and their complex architecture raises important questions regarding fluid migration and helictite architecture. In terms of their isotope geochemistry, helictites are depleted in 13C to various degrees, isotope values that are controlled by the mixing of fluids and mineralogy‐related fractionation. Regarding their δ18O values, most helictites overlap with other calcitic and aragonitic speleothems. Previous models explaining the twisted morphology of helictites are discussed from the viewpoint of fluid migration and CO2 degassing rates, mineralogy and helictite petrography. For the complex aragonitic helicities documented here, the most likely mechanisms to explain the contorted growth forms include the internal capillary network combined with localised (sector) growth at the helictite tip. The morphologically simpler calcitic helictites are best explained by capillary and surface flow. Future work should include geomicrobiology to assess the significance of induced mineralisation and transmission electron microscopy analysis to more quantitatively assign crystallographic properties. [ABSTRACT FROM AUTHOR]

Speleothem initial uranium isotope ratios ((234U/238U)i) can be influenced by processes along the seepage water flow‐path including alpha‐recoil into porewater during 238U decay and hostrock weathering, the balance of which can reflect the infiltration rate. Thus, speleothem (234U/238U)i may provide information about past changes in rainfall amounts. However, the utility of (234U/238U)i as a paleo‐infiltration proxy has only been explored in a limited set of rainfall regimes. We present a speleothem (234U/238U)i record from Mawmluh Cave in northeast India, an area influenced by the Indian Summer Monsoon, covering 1964–2012 CE. Speleothem (234U/238U)i was relatively constant from 1964 to 1984 but then linearly increased by 0.05 over ∼15 years, a trend that does not correspond with observed rainfall changes. To evaluate potential drivers of (234U/238U)i variability, we model the evolution of water (234U/238U) in a simple karst system using an advection‐reaction model parameterized by Mawmluh Cave variables. Although varying infiltration influences modeled water (234U/238U), the larger, sustained change observed in the speleothem record can only be modeled by varying the U concentration and (234U/238U) of the weathering hostrock. This suggests that larger shifts in speleothem (234U/238U)i may result from flow path changes, bringing waters in contact with hostrock of variable U characteristics. Consideration of published Mawmluh Cave records suggests that these mechanisms may also explain variability in stalagmite (234U/238U)i on precessional timescales. Further examination of speleothems (234U/238U)i from climates characterized by high rainfall and extensive weathering is warranted to better constrain the controls on (234U/238U)i in these dynamic environments. Plain Language Summary: Chemical indicators from stalagmites are useful in reconstructing changes in monsoon systems. However, the chemical measurements typically made on stalagmites do not provide direct reconstructions of rainfall amount. We developed a record of uranium isotope variability over the last 60 years in a stalagmite from Northeast India to evaluate this potential metric of past monsoon rainfall. We use a geochemical model to evaluate the climatic and environmental controls on uranium isotopes in cave drip waters and stalagmites. Comparison of our record with measured rainfall indicates that the relationship between rainfall amount and uranium isotope ratios is opposite to that observed in arid environments. Further, a large linear increase in uranium isotopes between ∼1985 and 2000 CE does not correspond to a change in rainfall. Rather, our model suggests that large changes in uranium isotopes likely result from the opening up of new water flow paths and the dissolution of fresh hostrocks. Investigation of previously analyzed stalagmites from the cave reveals a correspondence between uranium isotopes and insolation, suggesting that sustained changes in rainfall amount, coupled with opening of new flow paths, may be recorded in stalagmite uranium isotopes over the past ∼100,000 years. Key Points: Modern record of speleothem initial uranium isotope ratios from NE India shows a linear increase that does not correspond to rainfallGeochemical model shows that dripwater U isotopes respond to changing infiltration and changing U characteristics of weathering rockLong‐term variations in speleothem U isotope ratios from NE India record infiltration with additional control of changes in flow path [ABSTRACT FROM AUTHOR]

Seismic vulnerability of speleothems may serve long-term seismic risk studies. For this reason, the seismic response of stalagmite is computed using a robust FEM model calibrated from free vibration records by Hilbert–Huang modal extraction. It is demonstrated that the stalagmite vibrations consist of pairs of closely coupled flexural natural modes with a negligible role of vertical excitations. The location of the breaking point of the stalagmite is a result of a balance between the overturning bending moment and variations of horizontal cross-sections with height. Safety margins are investigated, and the ultimate peak velocity of excitations equaling 3.4 mm/s is estimated. [ABSTRACT FROM AUTHOR]

The complexity of processes affecting soil organic carbon (SOC) turnover on spatio‐temporal scales often hinders the extrapolation of results from specific sites to larger scales. This study presents Holocene speleothem U‐Th ages paired with 14C ages of carbonate and dissolved organic carbon (DOC) through three caves located on a north‐south transect through China. The deviations of speleothem 14CDOC ages from the U‐Th ages show clearly spatial variability, and they are positively correlated with mean ages of modern SOC and soil turnover time, suggesting that deviations can be used to infer the SOC turnover. We further demonstrate that slow SOC turnover (large deviation) was associated with weak monsoon (low temperature/less precipitation) on temporal scales. Our findings reveal that climate dominates the speleothem 14CDOC ages and SOC turnover. As global warming likely will intensify, the accelerated turnover of SOC, particularly at higher latitude areas, may partially offset the existing soil carbon stock. Plain Language Summary: Understanding the controls of the soil organic carbon (SOC) turnover on spatio‐temporal scales is of great significance to predict the soil carbon stock. The current knowledge of SOC turnover on the longer temporal scale is scarce due to a lack of accurate chronology. Here, we present Holocene speleothem U‐Th ages paired with 14C ages of carbonate and dissolved organic carbon (DOC) through three caves located on a north‐south transect through China. We found the deviations of speleothem 14CDOC ages from the baseline U‐Th ages positively and negatively correlated with soil turnover time and climate variables (i.e., temperature and precipitation), respectively. Concretely, long turnover time as indicated by large deviations was associated with weaker monsoon (low temperature and less precipitation), and vice versa. It suggests that climate dominates SOC turnover and the speleothem 14CDOC ages. Our study not only provides a compelling approach to diagnose the past cycling of SOC under climate shifts exceeding present‐day variability and but also projects a promising perspective for studying the interactions between SOC turnover rates and climate changes on broad spatio‐temporal scales. Meanwhile, it creates an opportunity to evaluate the changes in SOC turnover rates for the future. Key Points: Using 14C ages of dissolved organic carbon in speleothem as an alternative approach to date the speleothem is questionableThe deviations of speleothem 14CDOC from the U‐Th ages can be used to infer the turnover of the soil organic carbon (SOC)Climate dominates the speleothem 14CDOC ages and SOC turnover on spatio‐temporal scales [ABSTRACT FROM AUTHOR]

Cave rafts are found on the surface of still pools, usually in parts of caves or mines with little air movement. They are most commonly composed of calcium carbonate (CaCO3) in the form of calcite or aragonite, however there have been documented occurrences of gypsum, native sulphur and oxide rafts. Cave rafts are precipitated from supersaturated water in many settings including caves, mines, spring-fed rivers and under man-made concrete structures. Despite being very thin and fragile, rafts can create incredible structures that look like stalagmites when sunk in a constant location under a drip. Degassing of carbon dioxide (CO2) from solution is the prominent driving force causing the deposition of rafts in caves and mines, whereas deposition from solution derived from concrete is driven by absorption of CO2 from the atmosphere into solution. Free floating rafts can be classified as fine floating rafts, whereas rafts that are attached to a pool bank can grow thicker and develop into what are considered to be massive calcite crusts. Rafts in caves are classified as 'speleothems', however rafts created outside the cave environment are excluded due to the definition of the term. It is proposed that rafts created in or around man-made environments (outside caves) be classified as 'calthemites'. It is proposed that a drip hole resembling a splash cup, created in a pile of rafts, where the flakes have become fused together or lined with calcite should be called a "raft splash cup" a subtype of conulite. [ABSTRACT FROM AUTHOR]

Caves with hot springs and speleothem deposits are infrequent environments of high scientific interest due to their unique environmental conditions. The selected site is a small open cave with a hot spring and stalactites in the Aedipsos area (NW Euboea Island, Greece), which was studied through an interdisciplinary approach. The mineralogical composition of the speleothems was determined by optical microscopy, XRD, and SEM-EDS microanalysis, and identification of the Cyanobacteria species was made based on morphological characteristics. The main mineral phase in the studied samples is calcite, with several trace elements (i.e., up to 0.48 wt.% Na2O, up to 0.73 wt.% MgO, up to 4.19 wt.% SO3, up to 0.16 wt.% SrO and up to 2.21 wt.% Yb2O3) in the mineral-chemistry composition. The dominant facies are lamination and shrubs, which are the most common among the facies of the thermogenic travertines of the area. Based on the studied stalactites, twenty-nine different Cyanobacteria species were identified, belonging to the following orders: Synechococcales (28%), Oscillatoriales (27%), Chroococcales (21%) and Nostocales (21%), and Spirulinales (3%). Among them, thermophilic species (Spirulina subtilissima) and limestone substrate species (Chroococcus lithophilus, Leptolyngbya perforans, and Leptolyngbya ercegovicii) were identified. The identified Cyanobacteria were found to participate in biomineralization processes. The most characteristic biomineralization activity is made by the endolithic Cyanobacteria destroying calcite crystals in the outer layer. In a few cases, calcified cyanobacterial sheaths were detected. The presence of filamentous Cyanobacteria, along with extracellular polymeric substance (EPS), creates a dense net resulting in the retention of calcium carbonate crystals. [ABSTRACT FROM AUTHOR]

Coherent fluctuations in Sahel and Indian summer monsoon (ISM) rainfall influence the socio‐economic welfare of several densely populated regions. Here we identify a common mode of interannual rainfall variability over the Sahel and Indian regions and demonstrate the influence of both Pacific and Atlantic sea surface temperatures (SST) in inducing such a large‐scale response. The principal component of the leading mode of precipitation variability (PC1) over these regions correlates independently well with both ISM and Sahel rainfall indices. Here we show that this global SST‐driven dominant mode of Indo‐Sahel rainfall variability is well captured in present‐day rainfall δ18O and speleothem δ18O of the Ethiopian region. We use a ∼40‐year‐long monthly observational record of precipitation stable isotopes at Addis Ababa, Ethiopia to show that episodic isotopic depletions in rainfall at this site occur during the wet phases of PC1. These isotopic anomalies are associated with eastward intrusions of moisture initiating from the tropical Atlantic Ocean. Finally, we demonstrate decadal‐scale co‐variability between PC‐1 and a century‐long δ18O record from an actively growing Ethiopian speleothem to highlight the potential of rainfall isotopic records from this region to capture fluctuations in the coupled variability of the Indo‐African boreal monsoons. Plain Language Summary: Indian summer monsoon and Sahel summer rainfall exhibit substantial co‐variability on year‐to‐year and longer timescales. In this study, we identified a coherent mode of variability in Northern Hemisphere summer rainfall across these regions, which is remotely controlled by global‐scale sea surface temperature (SST) variability. Using long‐term (>40 years) rainfall oxygen isotope observations from Addis Abada, Ethiopia, we show that oxygen isotopic ratios in Ethiopian rainfall record these SST‐related variations in Indian and African boreal summer monsoons. We demonstrate the application of our hypothesis using a century‐long speleothem oxygen isotope record from an Ethiopian cave. These new findings offer possibilities for reconstructing this particular mode of variability of Indo‐African boreal summer monsoons from oxygen isotope‐based proxies from the Ethiopian region. Key Points: Ethiopian rainfall δ18O captures coherent Indo‐African rainfall variabilityEnhanced westerly moisture transport depletes Ethiopian rainfall δ18O during strong monsoon yearsCentury‐long speleothem δ18O from Ethiopia records covariability in summer rainfall over India and Sahel [ABSTRACT FROM AUTHOR]

The impacts of anthropogenic forcing on Indian summer monsoon (ISM) rainfall are obscure, partly due to limited availability of highly resolved hydroclimate proxy records as well as the highly regionalized nature of precipitation. Here, we report an annually‐resolved speleothem oxygen isotope record from Xianren Cave, southwestern China, which represents rainfall change over the broad ISM region. We find that the region has endured at least six decadal‐scale weak monsoon events in the past three hundred years. One of them, lasting from the early to mid 19th century, shares the similar gradual, persistent trend as the most recent decline in ISM rainfall and both have a magnitude substantially larger than the others dominated by natural variability. This early weak monsoon event occurred during a historical time of intensive deforestation in the region. We conclude that the ISM trend could have been altered by the changes in land‐use and land‐cover since the early 19th century. Plain Language Summary: It is difficult to determine when human activities started to have visible effects on precipitation change. Here, we present a well‐resolved Indian summer monsoon (ISM) rainfall record, based on stable isotope studies on speleothems collected from a cave in southwestern China. The oxygen isotope record shows that ISM rainfall has six multi‐decadal decreases in the past three hundred years. One of the corresponding monsoon weakening, lasting from the early to mid 19th century, cannot be simply explained by natural variations in the climate system. This prolonged weak monsoon event was likely caused by regional‐scale changes in land‐use and land‐cover, which can be supported by carbon isotope data in speleothems as well as increased deforestation in the region. We hereby propose that observable changes in the trend of ISM rainfall caused by human activities could have occurred as early as in the early 19th century. Key Points: A speleothem oxygen isotope record shows that the Indian summer monsoon (ISM) has endured six multi‐decadal weakening in the past 300 yearsThe monsoon weakening, from the early to mid 19th century, has a similar gradual, persistent trend as the most recent decline in monsoon rainfallRegional changes in land‐use and land‐cover may have altered the trend of the ISM since the early 19th century [ABSTRACT FROM AUTHOR]

The 4.2 ka event is widely presumed to be a globally widespread aridity event and has been linked to several episodes of societal changes across the globe. Whether this climate event impacted the cultural development in south-central China remains uncertain due to a lack of regional paleorainfall records. We present here stalagmite stable carbon isotope and trace element-based reconstruction of hydroclimatic conditions from south-central China. Our data reveal a sub-millennial scale (~5.6 to 4.3 ka) drying trend in the region followed by a gradual transition to wetter conditions during the 4.2 ka event (4.3-3.9 ka). Together with the existing archaeological evidence, our data suggest that the drier climate before 4.3 ka may have promoted the Shijiahe culture, while the pluvial conditions during the 4.2 ka event may have adversely affected its settlements in low-lying areas. While military conflicts with the Wangwan III culture may have accelerated the collapse of Shijiahe culture, we suggest that the joint effects of climate and the region's topography also played important causal roles in its demise. [ABSTRACT FROM AUTHOR]

Cloud and convective parameterizations strongly influence uncertainties in equilibrium climate sensitivity. We provide a proof‐of‐concept study to constrain these parameterizations in a perturbed parameter ensemble of the atmosphere‐only version of the Goddard Institute for Space Studies Model E2.1 simulations by evaluating model biases in the present‐day runs using multiple satellite climatologies and by comparing simulated δ18O of precipitation (δ18Op), known to be sensitive to parameterization schemes, with a global database of speleothem δ18O records covering the Last Glacial Maximum (LGM), mid‐Holocene (MH) and pre‐industrial (PI) periods. Relative to modern interannual variability, paleoclimate simulations show greater sensitivity to parameter changes, allowing for an evaluation of model uncertainties over a broader range of climate forcing and the identification of parts of the world that are parameter sensitive. Certain simulations reproduced absolute δ18Op values across all time periods, along with LGM and MH δ18Op anomalies relative to the PI, better than the default parameterization. No single set of parameterizations worked well in all climate states, likely due to the non‐stationarity of cloud feedbacks under varying boundary conditions. Future work that involves varying multiple parameter sets simultaneously with coupled ocean feedbacks will likely provide improved constraints on cloud and convective parameterizations. Plain Language Summary: Equilibrium climate sensitivity (ECS) is a key climate metric that quantifies the rise in global mean surface temperature in response to doubling of atmospheric CO2. Changes in hydroclimate, temperature extremes, and other aspects of future climate projections are closely tied to a model's ECS. For decades, ECS range has remained wide despite improvements from using multiple lines of evidence. One persistent source of this spread is related to cloud and convective processes, which occur at scales too small to be explicitly resolved, and thus require parameterizations to be represented in climate models. These parameterizations directly influence water isotopes by modulating simulated clouds and atmospheric circulation, and thus can be used to constrain model processes and identify model biases. In this work, we demonstrated that paleoclimate simulations are more parameter sensitive than the modern, highlighting the potential of past climates in discriminating cloud and convective parameterizations. Using satellite‐ and proxy‐model comparisons, we identified the top performing parameterizations which differ for each time period likely due to varying cloud feedbacks under diverse climatic forcing. Overall, our results provide a framework for fine‐tuning model representations using combined paleoclimate and satellite data, offering a unique opportunity to assess model uncertainties over a broader range of climate variability. Key Points: Paleoclimate relative to modern are more parameter sensitive, allowing for an assessment of uncertainties over a variety of climate forcingCertain simulations reproduced the δ18O of precipitation from paleoclimate proxies better than the default parameterizationNo single set of parameters works well in all climate states likely due to varying boundary conditions influencing cloud feedbacks [ABSTRACT FROM AUTHOR]

Reconstructing hydroclimate over the Common Era is essential for understanding the dominant mechanisms of precipitation change and improving climate model projections, which currently suggest Northeast Mexico will become drier in the future. Tree‐ring reconstructions have suggested regional rainfall is primarily controlled by Pacific sea‐surface temperatures (SSTs). However, tree ring records tend to reflect winter‐spring rainfall, and thus may not accurately record total annual precipitation. Using the first multiproxy speleothem record spanning the last millennium, combined with results from an atmospheric general circulation model, we demonstrate mean annual rainfall in Northeast Mexico is highly sensitive to Atlantic SST variability. Our findings suggest future precipitation in Northeast Mexico is more dependent upon the warming of Tropical Atlantic SSTs relative to the Tropical Pacific. Plain Language Summary: We use geochemical markers of past rainfall in a rock from a cave (speleothem) to show that warming in Atlantic sea‐surface temperatures (SSTs) increases the amount of precipitation in Northeast Mexico. These finding are surprising, since previous rainfall reconstructions using tree rings have suggested a warmer Atlantic decreases precipitation in the region. We used a climate model to show that warming in the Atlantic increases precipitation during the summer but decreases precipitation during the winter. Although winter precipitation only accounts for 8% of annual rainfall in this region, tree rings are more reflective of the winter precipitation response. This is the first speleothem record from NE Mexico over this time‐period and suggests that projections of future rainfall should emphasize relative changes in Atlantic SST variability because it has a major impact on annual precipitation. Key Points: We present the first speleothem record spanning the last millennium from NE Mexico using multiple geochemical proxiesIn contrast to tree ring reconstructions, we suggest regional precipitation is primarily controlled by Atlantic sea‐surface temperatures (SSTs)We utilize results from a forced‐SST climate model to further support our interpretation [ABSTRACT FROM AUTHOR]

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High‐resolution 230Th ages and stable isotope (δ18O and δ13C) records from a stalagmite that grew between 39 and 2 ka in Incesu Cave located in south‐central Anatolia allow us to evaluate paleoclimate conditions for growth periods during Marine Isotope Stage 3 (MIS3) and the Holocene. High δ18O values and Heinrich events H3 and H4 are observed during the MIS3 interval. After a dry period in the Younger Dryas, low values between ca. 10 and 5.3 ka suggest a transition to wet mid‐ to early Holocene conditions. In the early Holocene, there are drier periods at 9.4 and 10.3 ka, coincident with cooling events recorded in the North Atlantic sediments and, after 5.3 ka a relatively dry late Holocene is seen. The IN‐01 isotope record is in phase with general trends of speleothem records in Turkey and the Eastern Mediterranean but differs in detail at the millennial scale. The more depleted δ18O values of IN‐01 compared to those of Eastern Mediterranean speleothems during the Holocene indicate that central Anatolian winter rainfall was isotopically influenced by the same air mass trajectories derived from the North Atlantic and Mediterranean with an isotopic rain shadow effect. [ABSTRACT FROM AUTHOR]

Here we present an electrochemical method for the anodic oxidation and subsequent degradation of lignin in speleothems to utilize the resulting lignin oxidation products (LOPs) as paleo‐vegetation markers. LOPs were analyzed using an ultra‐high performance liquid chromatography (UHPLC) system coupled to a high‐resolution mass spectrometer (HRMS). The method presented here achieved comparable or even higher LOP concentrations than established CuO and CuSO4 oxidation methods. The method represents a new tool for the analysis and reconstruction of paleo‐vegetation and has the potential to be applied to other climate archives. [ABSTRACT FROM AUTHOR]

Recent paleoclimate reconstructions have suggested millennial‐scale variability in the Indo‐Pacific Warm Pool region coincident with events of the last deglaciation. Here, we present a new stalagmite oxygen isotope record from northern Borneo, which today is located near the center of the region's mean annual intertropical convergence zone. The record spans the full deglaciation, and reveals for the first time distinct oxygen isotope variations at this location connected with the Bølling‐Allerød onset and the Younger Dryas event. The full deglaciation in the Borneo stalagmite proxy reconstruction appears remarkably similar to a 20–11 ka transient simulation of rainfall over the area produced using the isotope‐enabled Community Earth System Model. In this model, periods of weakened Atlantic Ocean meridional overturning circulation are associated with an anomalous Western North Pacific anticyclone, which is produced in boreal autumn and shifts south over Borneo during boreal winter, causing dry conditions. Plain Language Summary: Here, we aim to resolve conflicting evidence of how tropical convection in Borneo in the Indo‐Pacific oceanic region, a critical region associated with El Niño events and the Asian and Australian‐Indonesian monsoon systems, was affected by past changes in the strength of Atlantic Ocean circulation. Analyzing a 20,000+ year old Borneo cave stalagmite along its growth axis, we find large oxygen isotope shifts coincident with two prominent millennial‐scale periods of reduced Atlantic Ocean overturning circulation strength. The isotope record is similar to a neighboring southwestern Philippine stalagmite record, and we interpret the signal as drier mean annual conditions over the region during these events compared to the background state; an interpretation supported by simulations in three independent state‐of‐the‐art climate models. One model suggests that these conditions in Borneo were driven by the southward shift of an anomalous anticyclone in the boreal winter season. By combining geochemical and model evidence, this study has shown that rainfall decreased for millennial periods during the end of the ice age, when the Atlantic Ocean overturning circulation weakened. In doing so, we have elucidated further how this region responds to major changes in global climate and ocean conditions. Key Points: A new stalagmite record reveals for the first time distinct Bølling‐Allerød and Younger Dryas oxygen isotope variations in northern BorneoThe stalagmite oxygen isotope pattern strongly resembles the recent iCESM transient annual rainfall simulation from 20 to 11 kaBorneo drying during Heinrich 1 and the Younger Dryas may be attributed to an anomalous boreal winter Western North Pacific anticyclone [ABSTRACT FROM AUTHOR]

We present new high‐resolution absolute‐dated stalagmite δ18O and δ13C records from Alabama, southeastern United States (SE US), spanning the last 12 thousand years (ka). A local relationship between annual rainfall amount and its amount‐weighed δ18O composition exists on interannual timescales, driven mostly by an amount effect during summer and spring seasons. Based on a novel quantitative interpretation of modern rainfall isotopic data, stalagmite δ18O variability is interpreted to reflect the relative contribution of summer and spring precipitation combined, relative to combined fall and winter precipitation. Precipitation amount in the SE US increases during an interval of 500 yr coeval with the Younger Dryas and during the 8.2 ka and Little Ice Age abrupt cooling events. High precipitation during these events reflects enhancement of spring and summer precipitation by 90% combined, relative to today's conditions, while the contribution of fall and winter rainfall remained unchanged or decreased slightly. Results from this study support model simulation results that suggest increased precipitation in the SE US during Atlantic Meridional Overturning Circulation (AMOC) slowdown/shutdown. In association with Northern Hemisphere mid‐latitude cooling from the Early to mid‐Holocene, annual precipitation in the SE US decreases, a pattern distinctive from that observed during abrupt cooling events related to AMOC shifts. Long‐term hydroclimate change in the SE US is likely sensitive to summer insolation reduction as inferred to have occurred in other tropical and subtropical regions. The dynamical link between AMOC shutdown and precipitation variability in the SE US remains to be examined. Plain Language Summary: We present a paleoclimate record from Alabama, United States, interpreted to reflect precipitation variability over the last 12 thousand years. This record suggests that precipitation in the southeastern United States (SE US) increased during rapid cooling events in the North Atlantic associated with the Younger Dryas, 8.2 ka and Little Ice Age events. We suggest that regional precipitation variability during these climatic events was linked to shifts in North Atlantic deep ocean formation. The implication of our study for the future is that if North Atlantic deep water formation slows down as a result of global warming, as suggested by recent observations and model simulations, the SE US region may experience a tendency to wetter conditions, particularly during the summer time. Key Points: Precipitation amount in the southeastern US likely increased during the Younger Dryas, the 8.2 ka and Little Ice Age abrupt cooling eventsHigh precipitation during these events likely reflected enhancement of spring and summer precipitationAtlantic Meridional Overturning Circulation shutdown could potentially help mitigate regional drought in the southeastern United States in the future [ABSTRACT FROM AUTHOR]

Palaeoclimate variability must be constrained to predict the nature and impacts of future climate change in the Eastern Mediterranean. Here, we present a late Holocene high‐resolution multiproxy data set from Kocain Cave, the first of its kind from SW Turkey. Regional fluctuations in effective‐moisture are recorded by variations in magnesium, strontium, phosphorous and carbon isotopes, with oxygen isotopes reacting to changes in precipitation and effective‐moisture. The new record shows a double‐peak of arid conditions at 1150 and 800 BCE, a wet period 330–460 CE followed by a rapid shift to dry conditions 460–830 CE, and a dry/wet Medieval Climate Anomaly/Little Ice Age pattern. Large discrepancies exist between Turkish records and the Kocain record, which shares more similarities with other Eastern Mediterranean coastal records. Heterogeneity of regional climate and palaeoclimate proxy records are emphasized. Plain Language Summary: Records of past climate are essential in the Eastern Mediterranean to understand regional impacts of modern climate change. In combination with archeology, these allow us to examine climatic impacts on people in the past to help us prepare for the future. Here, we examine a stalagmite (Ko‐1) from Kocain Cave, southwest Turkey, which contains information about past climate change in its chemistry. Measurements of trace‐metals and carbon isotope ratios record the amount of water entering the cave, oxygen isotope ratios record rainfall amount. Measurements of uranium are used to date the climate changes. Earthquakes that damaged nearby cities and caused tsunamis changed the angle of the stalagmite, providing more evidence for dating the sample. The Kocain Cave record shows climatic conditions changed frequently in southwest Turkey. Important are dry conditions 1150 and 800 BCE, wet conditions 330–460 CE followed by a rapid shift to dry conditions 460–830 CE, and a dry/wet Medieval Climate Anomaly/Little Ice Age pattern. These climate changes were different to records from elsewhere in Turkey and matched better with coastal records from Greece and Lebanon/Israel. The complex nature of past climate is emphasized due to varied climatic regions in Turkey and the many impacts on each record. Key Points: Stalagmite Ko‐1 record of effective‐moisture from SW Turkey stresses spatial and temporal heterogeneity of Turkish climateClimate changes share more similarities with other Eastern Mediterranean coastal regions, than central or northern TurkeyHeterogeneity of modern climate and proxy records highlight the complexity of historical comparisons [ABSTRACT FROM AUTHOR]

We examined 14 subaerially deposited speleothems retrieved from submerged caves in the northeastern Yucatán Peninsula (Mexico). These speleothems grew during the Middle to Late Quaternary and were dated by 230Th‐U techniques to provide upper depth limits for past sea levels. We report the first relative sea‐level limits for Marine Isotope Stages (MIS) 11 and 6, and present new evidence for sea‐level oscillations during MIS 5 and early MIS 1. For the latter periods, the origin of growth interruptions is evaluated by combining petrographic methods with trace element analyses. The MIS 5c sea‐level highstand probably occurred between 103.94 ± 0.58 ka and 96.82 ± 0.42 ka and must have exceeded ‐10.8 m (relative to present‐day local sea level). The minimum average rate of sea‐level fall over a 9.4 ka‐long period during the MIS 5e/5d transition is calculated from stalagmite and published coral data at 1.74 ± 0.37 m/ka. For the early Holocene, previous discrepancies with respect to a potential multimetre oscillation of local sea level were found to be challenging to reconcile with the existing speleothem data from the area. [ABSTRACT FROM AUTHOR]

The Balkan Peninsula represents one of the most important human pathways into and out of Europe during the Pleistocene. Mishin Kamik cave, located in the karst region of Western Stara Planina, has a rich faunal content and shows promising features indicating a human occupation site with the discovery of potential bone artefacts and an intriguing accumulation of bear skulls and bones. Petrographic study and U‐series dating of a stalagmite and other calcite deposits in the cave provide an absolute chronological frame for the detrital infillings and their archaeological content and inform the environmental and climatic context of the cave evolution. Most detrital deposits in the cave were probably deposited before Marine Isotope Stage (MIS) 5 and the cave morphology and sedimentary deposits display current morphologies since ~135 ka. Consequently, the palaeontological and archaeological findings are older than ~135 ka. Calcite dated on and under the accumulation of bear skulls and bones suggests deposition during MIS 7. A first depositional contextualization of the bone accumulation does not allow us to discriminate between a natural or anthropogenic origin. The study emphasizes the added value of speleothem studies in archaeological sites and particularly in bringing a well‐constrained chronological and environmental framework. [ABSTRACT FROM AUTHOR]

Orbital‐scale East Asian Summer Monsoon (EASM) variations inferred from loess deposits in northern China and speleothems from southern China display different dominant periods, complicating our understanding of monsoon response to insolation and ice‐volume forcings. Here we integrate a new microcodium δ18O record from a high‐resolution last interglacial loess profile with previously published data and provide a composite microcodium δ18O record on the Chinese Loess Plateau (CLP) since the last interglacial. The composite microcodium δ18O record displays distinct precessional cycles, consistent with speleothem δ18O records, but with different amplitude contrast (particularly during the peak interglacials). We propose that both loess and speleothem δ18O records exhibit covariations at precessional timescale oscillations. The discrepancy between loess and speleothem from southern China can be attributed to the influences of other processes besides summer precipitation on the proxies. A slight difference in amplitude between microcodium and speleothem δ18O records implies that the EASM is also influenced by inland surface boundary conditions, which has important impacts on the occurrence of EASM precipitation. Therefore, microcodium δ18O from the Chinese loess–paleosol sequences can be regarded as a representative proxy of EASM precipitation in northern China and then a reliable proxy reflecting the variation of EASM intensity. [ABSTRACT FROM AUTHOR]

We present the first stable isotope (δ13C and δ18O) speleothem record from continental Croatia retrieved from two coeval stalagmites from Nova Grgosova Cave. U-Th dates constrain the stalagmite growth history from 10 ka to the present, revealing coeval growth between 7.8 and 5.6 ka. We interpret δ18O as an autumn/winter hydrological proxy related to changes of vapor source, precipitation amount, and/or seasonal rainfall distribution, while δ13C predominantly responds to spring/summer vegetation status and soil microbial activity. We identify several centennial to millennial-scale hydroclimate oscillations during this period that result from multiple forcing factors. Along with amount and source effect, it appears that some centennial variations were governed also by seasonal moisture balance. From 9.2 to 8.8 ka BP, the local environmental setting was characterized by enhanced vegetation activity, while during the 8.2 ka event the main feature was a change in precipitation seasonality. The most prominent change, identified in both δ13C records, is a sudden decline of vegetation and soil biological activity around 7.4 ka, indicating a precipitation decrease at a time of maximum plant growth in spring and summer and likely also reduced precipitation in autumn and winter. Although small in magnitude in these speleothems, a peak in δ18O and δ13C values at 4.3–4.1 ka suggests that both summer and winter conditions were substantially drier during the 4.2 ka event, in accordance with increased Mediterranean aridity and consistent with other global climate changes reported at this time. Compared to the present North Atlantic Oscillation (NAO) influence, we assume that millennial Holocene NAO-like variations were persistent through the Holocene via their effect on modifying local/regional air temperature, vapor origin, and inter- and intrannual precipitation distribution. Anthropogenic deforestation, which was the first major human impact on the environment during the Neolithic agricultural revolution, is excluded as a leading factor in δ13C variability since the first sedentary settlements were established further to the east in more arable locations along river valleys. However, the impact of intensive mining around the cave site during the last millennium is evident, with substantial deforestation driving an increase in δ13C. [ABSTRACT FROM AUTHOR]

Songam Cave, a magnificent dolomite cave in the Democratic People’s Republic of Korea—is also known as “A Splendid Flower Cave”—is regarded as one of the renowned natural tourist attractions with a great number of beautiful and complicated aragonitic anthodites in different forms and shapes, together with diversified underground karst features (stalactite, stalagmite, limestone columns, flowstone, rimstone dams, botryoidal forms, pool spar, concretions, underground waterfall, ponds, etc.). This paper deals with the cave formation process, the features of speleothems and other karst features in Songam Cave, which indicate that Songam Cave is a geoheritage site of high conservation significance. The geological setting of the cave and the detailed features and diversity of the speleothems provide sufficient evidence to foster an understanding of the formation and development of the karst cave. The aragonitic anthodites and the outstanding underground karst features unfolded on the ceilings and walls throughout the cave suggest that Songam Cave can also be a cave tourist attraction of high aesthetic value. Overall, Songam Cave is a geoheritage of high conservative significance because of its geological and aesthetical value. [ABSTRACT FROM AUTHOR]

The European climate during the Holocene period is characterised by frequent changes of temperature and precipitation. The North Atlantic plays a major role as a driver for European climate and is a dominant precipitation source, particularly for the western European and north African realm. Atmospheric pressure gradients over the Atlantic (North Atlantic Oscillation, NAO), Atlantic circulation patterns (Atlantic Multidecadal Oscillation, AMO) or positioning of the Atlantic jet stream have been suggested to be responsible for precipitation patterns across western Europe. However, proxy data provide an inconsistent picture on how precipitation responds to changes in the Atlantic realm such as changes of Atlantic temperature (IRD), atmospheric pressure (NAO), water circulation (AMO) or the jet stream. Here we present a record of speleothem-based winter precipitation amount from Portugal. The record covers most of the Holocene and demonstrates that wetter conditions were synchronous in western and southern Iberia during early and mid Holocene. The record also shows a correlation between increased winter precipitation amount in western Iberia and Atlantic cooling, evidenced by Bond events, between 10 and 4 ka. [ABSTRACT FROM AUTHOR]

Speleothems are useful in detecting past geoenvironmental events. Variations in trace element concentrations may constitute a diagnostic of volcanic eruptions, enabling both dating and environmental impact assessment. This work attempts to detect possible 'signatures' of past volcanic eruptions in speleothems from Zoodochos Pigi cave on Santorini. Higher-than-usual concentrations of elements and minerals (e.g. barium and monazite respectively) exotic to typical speleothem chemistry in a band within a flowstone retrieved from the cave were revealed through SEM-EDS and XRD analyses and thought to be of volcanic origin. By chance, charcoal trapped in the said speleothem band allowed dating to establish the timing of the volcanic event. The radiocarbon date pointed towards the historically documented Hiera eruption, the earliest of a series of volcanic eruptions that postdate the Minoan eruption. The Hiera eruption, although less violent than the Minoan eruption, signallised the recrudescence of intracaldera activity which culminated in the formation of Palea Kameni (197 BC) with palpable effects on the regional environment. The interpretation of the results presented here, i.e. geochemical analysis on speleothems and radiocarbon dating, are cross-correlated with the well-documented timeline of eruptions of Santorini and ancient literature. [ABSTRACT FROM AUTHOR]

El Niño Southern Oscillation (ENSO) affects Indian Summer Monsoon (ISM) at interseasonal to interannual time scales. Given the heterogeneity in rainfall patterns over India, we have revisited the linkages between El Niño and ISM for the period 1600–2016 in this study. Our analysis based on the instrumental, paleo-proxy, model and satellite data sets show significant spatiotemporal variation in the ISM in response to El Niño. We observed strengthening of ISM over the northeast India (NEI) in conjunction with El Niño events. We suggest that the decadal trends in ISM over the NEI and central India (CI) were controlled by the long term variation in strength of El Niño events. We observed spatial variation in isoGSM derived rainfall and its oxygen isotopic composition (δ18O) in response to El Niño events. We further verified our observations from isotope proxy palaeo-records. Two high resolution speleothem (cave deposits) records of reconstructed ISM during 1600–2008 confirmed the inverse relation of rainfall patterns over CI (negative) and NEI (positive) during moderate to strong El Niño periods. These speleothem records infer a long-term pause in the El Niño (or stronger La Niña) like conditions, which were persisted during 1625–1715 and favored the stronger (weaker) rainfall over the CI (NEI). Furthermore, speleothem records showed stronger El Niño events during 1715–1760 causing significant reduction and enhancement in rainfall amount over CI and NEI, respectively. [ABSTRACT FROM AUTHOR]

The concept of geoheritage is related to places of geological interest, generally of aesthetic, cultural, socio-economic and/or scientific value. Many geosites are of karstic nature, because of their intrinsic beauty, their singularity and high geodiversity. Caves are among the most visited and economically exploited geological landforms. They constitute geosites as a whole, with their scenic landscapes, hydrogeological importance and the presence of bewildering natural rock and mineral formations including stalactites, stalagmites, flowstones and many other bizarre speleothem shapes. In some cases, a single speleothem, and the palaeoclimate record it contains, can be on its own of extraordinary importance to science. Once studied, these samples are often stored in research institution collections, rarely accessible to the wide public. In this paper, we report on the museumization of a stalagmite that has delivered a unique and exceptionally long glacial climate record from southern Italy, shedding light on the causes that led to the Neanderthal contraction and Modern Human expansion in this mild Mediterranean climate between 45 and 42 thousands years ago. The proposed museumization aims to demonstrate the potential of speleothems, after scientific application, in terms of educational and tourist resources. This approach allows to highlight the scientific importance of karst and cave geosites to the wide public, promoting their conservation and the valorisation of the studied cave-material. [ABSTRACT FROM AUTHOR]

This study examines the first precisely dated and temporally highly resolved speleothem record from Iberia that reconstructs the Oldest Dryas (OD). The onset of cold conditions in the study area, contemporary with the beginning of Heinrich Stadial 1, is recorded at 18.13 ± 0.08 ka, with a pronounced drop of 6.1‰ in δ13C in 250 years. Henceforth, stadial conditions depict a period of instability in the Atlantic Meridional Overturning Circulation, peaking in freshwater input from iceberg melting during Heinrich Event 1. Anomalies in the δ18O of the stalagmite attributed to such a freshwater event are found from 16.17 to 15.89 ka. Such absolute dates given to the onset of the OD in Iberia and to the main iceberg discharges are reliable anchor points for non-absolute chronologies. Two periods are identified in the OD: OD-a (18.13–16.17 ka) is characterized by wet conditions and a faster growth rate, and OD-b (15.89–14.81 ka) exhibits relative dryness and a slower growth rate. The sudden release of fresh water is considered to be the reason for the disruption of rainfall patterns in eastern Iberia. The present study also highlights the existence of heterogeneous and complex hydrological conditions during the OD in Iberia when both Atlantic and Mediterranean realms are considered. [ABSTRACT FROM AUTHOR]

During each Heinrich stadial (HS), temperatures in southern Europe typically dropped several degrees during several hundred to few thousand years. We have developed a one-dimensional thermal conduction model that transfers the typical surface temperature anomaly of a HS to a series of hypothetical underlying caves. The results show that with increasing depth, the thermal anomaly is attenuated, the lag time increases, and the signal structure experiences larger modifications. The model suggests that in most cases, it is not acceptable to assume a synchronous thermal variability and similar average temperature values between the surface atmosphere and the cave interior at millennial timescales. We also simulated the thermal impact of the modeled HS on speleothem δ18O records. The outputs of most model scenarios suggest that temperature changes associated with the HS produce δ18O anomalies capable of contributing significantly or even decisively to the speleothem isotope variability. Therefore, despite controls other than temperature often being considered more important when interpreting Pleistocene speleothem δ18O records in temperate climates, this research suggests that temperature is expected to be one of the major controls of δ18O values in most cave sites outside the tropics and should be included as a significant parameter affecting Pleistocene speleothem δ18O records. [ABSTRACT FROM AUTHOR]

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]