Speleothem Paleoclimatology for the Caribbean, Central America, and North America

Speleothem oxygen isotope records from the Caribbean, Central, and North America reveal climatic controls that include orbital variation, deglacial forcing related to ocean circulation and ice sheet retreat, and the influence of local and remote sea surface temperature variations. Here, we review these records and the global climate teleconnections they suggest following the recent publication of the Speleothem Isotopes Synthesis and Analysis (SISAL) database. We find that low-latitude records generally reflect changes in precipitation, whereas higher latitude records are sensitive to temperature and moisture source variability. Tropical records suggest precipitation variability is forced by orbital precession and North Atlantic Ocean circulation driven changes in atmospheric convection on long timescales, and tropical sea surface temperature variations on short timescales. On millennial timescales, precipitation seasonality in southwestern North America is related to North Atlantic climate variability. Great Basin speleothem records are closely linked with changes in Northern Hemisphere summer insolation. Although speleothems have revealed these critical global climate teleconnections, the paucity of continuous records precludes our ability to investigate climate drivers from the whole of Central and North America for the Pleistocene through modern. This underscores the need to improve spatial and temporal coverage of speleothem records across this climatically variable region

Last glacial millennial-scale hydro-climate and temperature changes in Puerto Rico constrained by speleothem fluid inclusion δ18^{18}O and δ2^{2}H values

We present speleothem fluid inclusion δ18Of and δ2Hf values from Larga Cave, Puerto Rico, that cover the interval between 46.2 and 15.3 ka on the millennial scale, including the Last Glacial Maximum (LGM) and several stadial and interstadial cycles. The data set can be divided in two main clusters of stable isotope compositions of the fluid inclusion water with respect to the global meteoric water line (GMWL), which coincide with strong variations in the water content of the stalagmite. In particular, this clustering is found to be climate related, where one cluster comprises samples from cold and dry periods, such as the Heinrich and Greenland stadials (HSs and GSs), as well as parts of the LGM, which exhibit very high δ18Of and δ2Hf values. We interpret this enrichment as being caused by evaporation inside the cave due to enhanced cave ventilation during these colder and drier times. In contrast, in most samples corresponding to warmer and wetter Greenland interstadials (GIs), but also for some from HS 2 and 3, the δ18Of and δ2Hf values plot on the meteoric water line and modification of fluid inclusion water due to “in-cave” evaporation are found to be negligible. Consequently, variations of recent glacial hydro-climate and temperatures in the western tropical Atlantic can be constrained. In general, δ18Of values from fluid inclusions are up to 3 ‰ higher than those of modern drip water, which is interpreted as a weaker atmospheric convective activity during the last glacial period. In addition, reconstructed temperatures suggest an average cooling of 2–3 ◦C during the LGM compared to modern cave temperatures. Reconstructed cave temperatures yield an average cooling of −1.4 ± 2.8 ◦C for HS 2 and −3.6 ± 2.2 ◦C for HS 3. Higher δ18Of values of these samples further suggest that the drip water was dominated by orographic rainfall and/or cold fronts, along with weak or even absent convective activity. In contrast, during intersta-dial phases, reconstructed temperatures reached nearly modern values, and convective activity was comparable to or only slightly weaker than today

Evaluating model outputs using integrated global speleothem records of climate change since the last glacial

Although quantitative isotopic data from speleothems has been used to evaluate isotope-enabled model simulations, currently no consensus exists regarding the most appropriate methodology through which to achieve this. A number of modelling groups will be running isotope-enabled palaeoclimate simulations in the framework of the Coupled Model Intercomparison Project Phase 6, so it is timely to evaluate different approaches to use the speleothem data for data-model comparisons. Here, we illustrate this using 456 globally-distributed speleothem δ18O records from an updated version of the Speleothem Isotopes Synthesis and Analysis (SISAL) database and palaeoclimate simulations generated using the ECHAM5-wiso isotope-enabled atmospheric circulation model. We show that the SISAL records reproduce the first-order spatial patterns of isotopic variability in the modern day, strongly supporting the application of this dataset for evaluating model-derived isotope variability into the past. However, the discontinuous nature of many speleothem records complicates procuring large numbers of records if data-model comparisons are made using the traditional approach of comparing anomalies between a control period and a given palaeoclimate experiment. To circumvent this issue, we illustrate techniques through which the absolute isotopic values during any time period could be used for model evaluation. Specifically, we show that speleothem isotope records allow an assessment of a model’s ability to simulate spatial isotopic trends. Our analyses provide a protocol for using speleothem isotopic data for model evaluation, including screening the observations to take into account the impact of speleothem mineralogy on 18O values, the optimum period for the modern observational baseline, and the selection of an appropriate time-window for creating means of the isotope data for palaeo time slices

Trace element data covering 96-7 ka BP from stalagmite CM (Santo Tomas Cave, Cuba)

We present a new speleothem trace element and stable isotope record, which extends previous paleoclimate evidence from Cuban speleothems to the last 96 ka. Stable isotope samples were micromilled at a resolution of 0.10-0.33mm, and measured using an IRMS equipped with a Gasbench. Line scans of Element/Calcium ratios of the speleothem were measured by laser ablation ICPMS and were reduced to the resolution of the stable isotope records

Stable isotopes covering 96-7 ka BP from stalagmite CM (Santo Tomas Cave, Cuba)

We present a new speleothem trace element and stable isotope record, which extends previous paleoclimate evidence from Cuban speleothems to the last 96 ka. Stable isotope samples were micromilled at a resolution of 0.10-0.33mm, and measured using an IRMS equipped with a Gasbench. Line scans of Element/Calcium ratios of the speleothem were measured by laser ablation ICPMS and were reduced to the resolution of the stable isotope records

Early Holocene (c. 11.0 - 9.5 ka BP) trace element data from stalagmite NAH14, north-eastern Yucatan Peninsula

This dataset from a speleothem record from the north-eastern Yucatán peninsula (Mexico) provides a high reslution stable isotope and trace elemental record for the early Holocene between 11,040 and 9,520 a BP on up to sub-decadal scale. Line scans of Element/Calcium ratios of the speleothem were measured by laser ablation ICPMS. The chronology is based on 17 U-Th ages (Warken et al., 2021) calculated with the half lives of Cheng et al., 2013. The age-depth model was constructed using the algorithm COPRA (Breitenbach et al., 2012)

Early Holocene (c. 11.0 - 9.5 ka BP) stable isotope data from stalagmite NAH14, north-eastern Yucatan Peninsula

This dataset from a speleothem record from the north-eastern Yucatán peninsula (Mexico) provides a high reslution stable isotope record for the early Holocene between 11,040 and 9,520 a BP on up to sub-decadal scale. Stable isotope samples were micromilled at a resolution of 0.25mm, and measured using an IRMS equipped with a Gasbench. The chronology is based on 17 U-Th ages (Warken et al., 2021) calculated with the half lives of Cheng et al., 2013. The age-depth model was constructed using the algorithm COPRA (Breitenbach et al., 2012)

Stable isotope, trace element and radiometric dating data covering 46.2-15.5 ka BP from stalagmite PR-LA-1 (Cueva Larga, Puerto Rico)

We present results of Th/U dating, stable isotope and trace element data from a speleothem from Puerto Rico. Th/U dating was performed using isotope dilution MC-ICPMS. Activity ratios were corrected for initial Th assuming an detrital weight ratio 232Th/238U = 0.154 ± 0.038 (corresponding to an activity ratio of the detritus in secular equilibrium of (230Th/232Th)detr = 19.79 ± 4.93), and secular equilibrium of the detritus. Ages are calculated using the decay constants by Cheng et al. (2000)). Uncertainties are given as 2σ- range, and do not include half-life uncertainties. Th/U dating shows that stalagmite PR-LA-1 covers the period from 15.4 to 46.2 ka with a growth interruption between 35.5 and 41.1 ka. Stable isotope samples were drilled with a spatial resolution of 1 mm and measured using an IRMS equipped with a Gasbench. Element/Calcium ratios of the speleothem were measured by laser ablation ICPMS and were reduced to the resolution of the stable isotope records

230Th/U-dating of subaqueous grown speleothems (Hells Bells) from the northeastern Yucatán Peninsula

This dataset contains 73 U-Th ages of subaqueous grown speleothems (Hells Bells) from the north-eastern Yucatán Peninsula. These secondary carbonates were collected from three different sinkholes (cenotes) southwest of Cancún, Quintana Roo, Mexico (20.51–20.52°N, 87.01–87.07°W) at water depths between -29.4 m a.s.l and -37.3 m a.s.l. Samples were collected in situ and their elevation was measured with a dive computer (+-0.1m). For samples taken from the bottom of the cenotes, we cannot assign a corresponding water depth since we have no information about their original position on the cave ceiling. The measurements were carried out by a multi-collector inductively coupled plasma mass spectrometer (ThermoFisher Neptune Plus)

Trace element and stable isotope data of subaqueous grown speleothems (Hells Bells) from the northeastern Yucatán Peninsula

This dataset provides geochemical data (trace elements and stable isotopes) of subaqueous grown speleothems (Hells Bells) from the north-eastern Yucatán Peninsula. These secondary carbonates were collected from three different sinkholes (cenotes) southwest of Cancún, Quintana Roo, Mexico (20.51–20.52°N, 87.01–87.07°W) at water depths between -29.4 m a.s.l and -37.3 m a.s.l. Samples were collected in situ and their elevation was measured with a dive computer (+-0.1m). For samples taken from the bottom of the cenotes, we cannot assign a corresponding water depth since we have no information about their original position on the cave ceiling. Major and trace elements were determined by ICP-OES. Stable carbon and oxygen isotope measurements were carried out by a ThermoFinnigan MAT253Plus gas source mass spectrometer equipped with a Thermo Fisher Scientific Kiel IV carbonate device