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Reconstructing the spatio-temporal dynamics of glaciations and permafrost largely relies on surface deposits, and is therefore a challenge for every glacial older than the last due to erosion. Consequently, glaciations and permafrost remain poorly constrained worldwide before c. 30 ka. Since speleothems (carbonate cave deposits) form from drip water and generally indicate the absence of an ice sheet and permafrost, we evaluate how speleothem growth phases defined by U-series dates align with past glacial-interglacial cycles. Further, we make the first systematic comparison of the spatial distribution of speleothem dates with independent reconstructions of the history of the British-Irish Ice Sheet (BIIS) to test how well geomorphologic ice reconstructions are replicated in the cave record. The frequency distribution of 1,020 U-series dates based on three different dating methods between 300 and 5 ka shows statistically significant periods of speleothem growth during the last interglacial and several interstadials during the last glacial. A pronounced decline in speleothem growth coincides with the Last Glacial Maximum, before broad reactivation during deglaciation and into the Holocene. Spatio-temporal patterns in speleothem growth between 31 and 15 ka agree well with the surface-deposit-based reconstruction of the last BIIS. In data-rich regions, such as northern England, ice dynamics are well-replicated in the cave record, which provide additional evidence about the spatio-temporal distribution of permafrost dynamics. Beyond the Last Glacial Maximum, the distribution of speleothem dates across the British Isles offers the opportunity to improve chronological constraints on past ice sheet variability, with evidence for a highly dynamic Scottish ice sheet during the last glacial. The results provide independent evidence of ice distribution complementary to studies of surface geomorphology and geology, and the potential to extend reconstructions into permafrost and earlier glacial cycles. Whilst undersampling is currently the main limitation for speleothem-based ice and permafrost reconstruction even in relatively well-sampled parts of the British Isles, we show that speleothem dates obtained using modern mass spectrometry techniques reveal a higher spatio-temporal resolution of glacial-interglacial cycles and glacial extent than previously possible. Further study of leads and lags in speleothem growth compared to surface deposition may provide new insights into landscape-scale dynamics during ice sheet growth and retreat. [ABSTRACT FROM AUTHOR]

The Cryogenian period (720–635 million years ago) in the Neoproterozoic era featured two phases of global or near-global ice cover termed "snowball Earth". Climate models of all kinds indicate that the inception of these phases must have occurred in the course of a self-amplifying ice–albedo feedback that forced the climate from a partially ice-covered to a snowball state within a few years or decades. The maximum concentration of atmospheric carbon dioxide (CO2) allowing such a drastic shift depends on the choice of model, the boundary conditions prescribed in the model, and the amount of climatic variability. Many previous studies reported values or ranges for this CO2 threshold but typically tested only a very few different boundary conditions or excluded variability due to volcanism. Here we present a comprehensive sensitivity study determining the CO2 thresholds in different scenarios for the Cryogenian continental configuration, orbital geometry, and short-term volcanic cooling effects in a consistent model framework using the climate model of intermediate complexity CLIMBER-3 α. The continental configurations comprise two palaeogeographic reconstructions for each of both snowball-Earth onsets as well as two idealised configurations with either uniformly dispersed continents or a single polar supercontinent. Orbital geometries are sampled as multiple different combinations of the parameters obliquity, eccentricity, and argument of perihelion. For volcanic eruptions, we differentiate between single globally homogeneous perturbations, single zonally resolved perturbations, and random sequences of globally homogeneous perturbations with realistic statistics. The CO2 threshold lies between 10 and 250 ppm for all simulations. While the thresholds for the idealised continental configurations differ by a factor of up to 19, the CO2 thresholds for the continental reconstructions differ by only 6 %–44 % relative to the lower thresholds. Changes in orbital geometry account for variations in the CO2 threshold of up to 30 % relative to the lowest threshold. The effects of volcanic perturbations largely depend on the orbital geometry and the corresponding structure of coexisting stable states. A very large peak reduction in net solar radiation of 20 or 30 W m -2 can shift the CO2 threshold by the same order of magnitude as or less than the orbital geometry. Exceptionally large eruptions of up to -40 W m -2 shift the threshold by up to 40 % for one orbital configuration. Eruptions near the Equator tend to, but do not always, cause larger shifts than eruptions at high latitudes. The effects of realistic eruption sequences are mostly determined by their largest events. In the presence of particularly intense small-magnitude volcanism, this effect can go beyond the ranges expected from single eruptions. [ABSTRACT FROM AUTHOR]

Abrupt first-order shifts in strontium and phosphorus concentrations in stalagmite calcite deposited in western Ireland during the 8200-year event (the major cooling episode 8200 years before the present) are interpreted as responses to a drier climate lasting about 37 years. Both shifts are centered on 8330 ± 80 years before the present, coinciding with a large oxygen isotope anomaly and a change in the calcite petrography. In this very high resolution (monthly) record, antipathetic second-order oscillations in phosphorus and strontium reveal decreased growth rates and increased rainfall seasonality. Growth rate variations within the event reveal a two-pronged structure consistent with recent model simulations., The 8200-year event is widely regarded as the strongest Holocene cooling episode, with clear expressions in Greenland (1, 2), the North Atlantic (3), Europe (4-11), North America (12-14), North Africa [...]

The article informs about a research based on intertropical convergence zone variability in the Neotropics during the Common Era. Topics discussed include changes in hydro climate in the Neotropics implied by proxy evidence; seasonally resolved stalagmite rainfall proxy data from the modern northern limit; and current trends of increased social unrest and mass migration; and influence on Central American precipitation is more seen on the Pacific Coast.

Speleothem organic matter can be a powerful tracer for past environmental conditions and karst processes. Carbon isotope measurements (δ13C and 14C) in particular can provide crucial information on the provenance and age of speleothem organic matter, but are challenging due to low concentrations of organic matter in stalagmites. Here, we present a method development study on extraction and isotopic characterization of speleothem organic matter using a rapid procedure with low laboratory contamination risk. An extensive blank assessment allowed us to quantify possible sources of contamination through the entire method. Although blank contamination is consistently low (1.7 ± 0.34 – 4.3 ± 0.86 μg C for the entire procedure), incomplete sample decarbonation poses a still unresolved problem of the method, but can be detected when considering both δ13C and 14C values. We test the method on five stalagmites, showing reproducible results on samples as small as 7 μg C for δ13C and 20 μg C for 14C. Furthermore, we find consistently lower non-purgeable organic carbon (NPOC) 14C values compared to the carbonate 14C over the bomb spike interval in two stalagmites from Yok Balum Cave, Belize, suggesting overprint of a pre-aged or even fossil source of carbon on the organic fraction incorporated by these stalagmites. [ABSTRACT FROM AUTHOR]

The Younger Dryas is considered the archetypal millennial-scale climate change event, and identifying its cause is fundamental for thoroughly understanding climate systematics during deglaciations. However, the mechanisms responsible for its initiation remain elusive, and both of the most researched triggers (a meltwater pulse or a bolide impact) are controversial. Here, we consider the problem from a different perspective and explore a hypothesis that Younger Dryas climate shifts were catalysed by the unusually sulfurrich 12.880±0.040 ka BP eruption of the Laacher See volcano (Germany). We use the most recent chronology for the GISP2 ice core ion dataset from the Greenland ice sheet to identify a large volcanic sulfur spike coincident with both the Laacher See eruption and the onset of Younger Dryasrelated cooling in Greenland (i.e. the most recent abrupt Greenland millennial-scale cooling event, the Greenland Stadial 1, GS-1). Previously published lake sediment and stalagmite records confirm that the eruption's timing was indistinguishable from the onset of cooling across the North Atlantic but that it preceded westerly wind repositioning over central Europe by ~200 years. We suggest that the initial short-lived volcanic sulfate aerosol cooling was amplified by ocean circulation shifts and/or sea ice expansion, gradually cooling the North Atlantic region and incrementally shifting the midlatitude westerlies to the south. The aerosol-related cooling probably only lasted 1-3 years, and the majority of Younger Dryas-related cooling may have been due to the seaice-ocean circulation positive feedback, which was particularly effective during the intermediate ice volume conditions characteristic of ~13 ka BP. We conclude that the large and sulfur-rich Laacher See eruption should be considered a viable trigger for the Younger Dryas. However, future studies should prioritise climate modelling of high-latitude volcanism during deglacial boundary conditions in order to test the hypothesis proposed here. [ABSTRACT FROM AUTHOR]

The Younger Dryas is the most well-documented millennial-scale cooling event of the Quaternary, but the mechanisms responsible for its initiation remain elusive. Here we use a recently revised chronology for the GISP2 ice core ion dataset to identify a large volcanic sulphur spike coincident with both the sulphur-rich Laacher See volcanic eruption and the onset of Younger Dryas-related cooling (GS-1) in Greenland. Lake sediment and stalagmite records confirm that the eruption's timing was indistinguishable from the onset of cooling across the North Atlantic, but that it preceded westerly wind repositioning over central Europe by ~ 200 years. We suggest that the initial short-lived volcanic sulphate aerosol cooling was amplified by oceanic circulation shifts or sea ice expansion, gradually cooling the North Atlantic region and incrementally shifting the mid-latitude westerlies to the south. The aerosol-related cooling probably only lasted 2-4 years, and the majority of Younger Dryas-related cooling was instead due to this positive feedback, which was particularly effective during the intermediate ice volume conditions characteristic of ~ 13 ka BP. We conclude that the large and sulphur-rich Laacher See eruption should be considered a viable trigger for the Younger Dryas. [ABSTRACT FROM AUTHOR]

The nature of cave ventilation is of interest to cavers, speleologists, and paleoclimatologists working with stalagmites. Because cave ventilation systematics may change over the growth span of a stalagmite, understanding what factors affect them is critical for determining events that may have affected climate proxies within the stalagmite. Similarly, understanding how the hydrology of the drips feeding a stalagmite evolves through time is key to building robust records of paleoclimate, particularly because stalagmite records have become critical archives of climate change information of the last 500,000 years. Here we present data from an extensive, on-going monitoring effort at Yok Balum Cave, Belize, initiated in 2011, that characterizes high-resolution ventilation dynamics at this site. Clear seasonal ventilation regimes exist, driven by thermally induced inside-outside air density differences. The winter regime is dominated by air inflow into the cave, decreased drawdown from the epikarst into the cave, and a limited diurnal signal. Conversely, summer ventilation is dominated by air outflow from the cave, greater CO2 drawdown and drip water degassing, and a strong diurnal signal. Active monitoring during a large (M7.4) earthquake in November 2012 provides a unique opportunity to assess the response of the cave atmosphere and hydrology to substantial seismic activity. Cave atmosphere dynamics and hydrology are found to be highly resilient to seismic activity, with no observable disturbance occurring around the earthquake, despite there being considerable evidence of physical disruption in the cave. Monitoring included different kinds of drips, and the earthquake affected none of the monitored drip types. This suggests that stalagmite-derived paleoclimate records are not affected by seismic activity, except in extreme cases where the stalagmite or conjugate stalactite is damaged or reoriented. [ABSTRACT FROM AUTHOR]