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Cave carbonate minerals are an important terrestrial paleoclimate archive. A few studies have explored the potential for applying carbonate clumped isotope thermometry to speleothems as a tool for constraining past temperatures. To date, most papers utilizing this method have focused on mass-47 clumped isotope values (Δ47) at a single location and reported that cave carbonate minerals rarely achieve isotopic equilibrium, with kinetic isotope effects (KIEs) attributed to CO2 degassing. More recently, studies have shown that mass-47 and mass-48 CO2 from acid digested carbonate minerals (Δ47 and Δ48) can be used together to assess equilibrium and probe KIEs. Here, we examined 44 natural and synthetic modern cave carbonate mineral samples from 13 localities with varying environmental conditions (ventilation, water level, pCO2, temperature) for (dis)equilibrium using Δ47-Δ48 values, in concert with traditional stable carbon (δ13C) and oxygen (δ18O) isotope ratios. Data showed that 19 of 44 samples exhibited Δ47-Δ48 values indistinguishable from isotopic equilibrium, and 18 (95 %) of these samples yield Δ47-predicted temperatures within error of measured modern temperatures. Conversely, 25 samples exhibited isotopic disequilibria, 13 of which yield erroneous temperature estimates. Within some speleothem samples, we find Δ47-Δ48 values consistent with CO2 degassing effects, however, the majority of samples with KIEs are consistent with other processes being dominant. We hypothesize that these values reflect isotopic buffering effects on clumped isotopes that can be considerable and cannot be overlooked. Using a Raleigh Distillation Model, we examined carbon and oxygen isotope exchange trajectories and their relationships with dual clumped isotope disequilibria. Carbon isotope exchange is associated with depletion of both Δ47 and Δ48 relative to equilibrium, while oxygen isotope exchange is associated with enrichment of both Δ47 and Δ48 relative to equilibrium. Cave rafts collected from proximate locations in Mexico exhibit the largest average departures from equilibrium (ΔΔ47¯ = −0.032 ± 0.007, ΔΔ48¯ = −0.104 ± 0.035, where ΔΔi is the measured value – the equilibrium value). This study shows how the Δ47-Δ48 dual carbonate clumped isotope framework can be applied to a variety of tcave carbonate mineral samples, enabling identification of isotopic equilibria and therefore quantitative application of clumped isotope thermometry for paleoclimate reconstruction, or alternatively, constraining the mechanisms of kinetic effects.

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.

The timing and mechanisms of past hydroclimate change in northeast Mexico are poorly constrained, limiting our ability to evaluate climate model performance. To address this, we present a multiproxy speleothem record of past hydroclimate variability spanning 62.5 to 5.1 ka from Tamaulipas, Mexico. Here we show a strong influence of Atlantic and Pacific sea surface temperatures on orbital and millennial scale precipitation changes in the region. Multiple proxies show no clear response to insolation forcing, but strong evidence for dry conditions during Heinrich Stadials. While these trends are consistent with other records from across Mesoamerica and the Caribbean, the relative importance of thermodynamic and dynamic controls in driving this response is debated. An isotope-enabled climate model shows that cool Atlantic SSTs and stronger easterlies drive a strong inter-basin sea surface temperature gradient and a southward shift in moisture convergence, causing drying in this region.

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.

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]