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1. Uranium-Thorium ages and stable oxygen isotope data on speleothems that grew during Marine Isotope Stages (MIS) 11, 9, and 5e, Northwest Territories, Canada, 2024

   https://doi.org/10.18739/A2SJ19S7M  

   Batchelor, Cameron; McGee, David; Shakun, Jeremy; Woodhead, Jon; Jost, Adam; Arnold, Sarah; Horne, Greg; Kinsley, Christopher; Freudenburg-Puricelli, Markey (January 2024, NSF Arctic Data Center)

   High-resolution records from past interglacial climates help constrain future responses to global warming, yet are rare. This dataset contains seasonally-resolved climate records from subarctic-Canada using micron-scale measurements of oxygen isotopes (δ18O) in speleothems with apparent annual growth bands from three interglacial periods – Marine Isotope Stages 11 (409-376 ka), 9 (336-305 ka) and MIS 5e (123-118 ka). Our study highlights the potential for high-latitude speleothems to yield detailed isotopic records of Northern Hemisphere interglacial climates beyond the reach of Greenland ice cores and offers a framework for interpreting them. Table S1 contains the Uranium-Thorium dates for six speleothems, or more specifically, flowstones, from a cave in Northwest Territories (NWT), Canada. It also contains constructed age models for each sample. Then, we applied a two-tiered methodological approach to reconstruct past subarctic climate. First, we produce an ultra-high-resolution δ18O record that, although not continuous, spans thousands of years for portions of these interglacials. This record was created using Secondary Ion Mass Spectrometry (SIMS) to measure δ18O approximately every 35-micrometer (µm) down each sample’s growth axis. This data is shown in Table S2. Second, we used Confocal Laser Fluorescence Microscopy (CLFM) to identify several fluorescent annual bands in each speleothem, which we then targeted for additional SIMS measurements. This data is shown in Table S3. Though these subarctic speleothems are small in size (most are less than 10 centimeter (cm) in length), the application of both CLFM and SIMS on these samples demonstrate their potential for providing ultra-high-resolution records of high-latitude Northern Hemisphere terrestrial climate outside of Greenland and provide insights into interpretive frameworks for future cold-region speleothem δ18O records. 

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2. A new MIS 5 to MIS 2 speleothem record from Sandkraal Cave on the South African Cape south coast

   https://doi.org/10.1017/qua.2024.3  

   Braun, Kerstin; Bar-Matthews, Miryam; Ayalon, Avner; Matthews, Alan; Zilberman, Tami; Zolotova, Natalya; Cowling, Richard M.; Karkanas, Panagiotis; Cawthra, Hayley C.; Fisher, Erich C.; et al (March 2024, Quaternary Research)

   Abstract We present new stable oxygen and carbon isotope composite records (δ¹⁸O, δ¹³C) of speleothems from Sandkraal Cave 1 (SK1) on the South African south coast for the time interval between 104 and 18 ka (with a hiatus between 48 and 41 ka). Statistical comparisons using kernel-based correlation analyses and semblance analyses based on continuous wavelet transforms inform the relationships of the new speleothem records to other proxies and their changes through time. Between 105 and ~70 ka, changes of speleothem δ¹⁸O values at SK1 are likely related to rainfall seasonality. Variations of δ¹³C values are associated with changes of vegetation density, prior carbonate precipitation (PCP), CO₂degassing in the cave, and possibly variations of the abundance of C₃and C₄grasses in the vegetation. The relationships of δ¹⁸O with other proxies shift between ~70 and 48 ka (Marine Isotope Stages 4–3) so that both stable isotope records now reflect CO₂degassing, evaporation, and PCP. Similar relationships also continue after the hiatus for the deposition phase between 42 and 18 ka. Our findings support modeling results suggesting drier conditions in the study area when the Southern Hemisphere westerlies are shifted north and the paleo–Agulhas Plain is exposed. 

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3. Seasonally Variable Aquifer Discharge and Cooler Climate in Bermuda During the Last Interglacial Revealed by Subannual Clumped Isotope Analysis

   https://doi.org/10.1029/2020PA004145  

   Zhang, Jade Z.; Petersen, Sierra V.; Winkelstern, Ian Z.; Lohmann, Kyger C. (May 2021, Paleoceanography and Paleoclimatology)

   Abstract Faunal analog reconstructions suggest that Last Interglacial (MIS 5e) sea surface temperatures were cooler around Bermuda and in the Caribbean than modern climate. Here we describe new and revised clumped isotope measurements ofCittarium picafossil shells supporting previous findings of cooler than modern temperatures in Bermuda during the Last Interglacial. We resolve temperature and δ¹⁸O_wdifferences between two closely located and apparently coeval sites described in Winkelstern et al. (2017),https://doi.org/10.1002/2016pa003014through reprocessing raw isotopic data with the updated Brand/IUPAC parameters. New subannual‐resolution clumped isotope data reveal large variations in δ¹⁸O_wout of phase with seasonal temperature changes (i.e., lower δ¹⁸O_wvalues in winter). Supported by modern δ¹⁸O_wmeasurements identifying similar processes occurring today, we suggest past variations in coastal δ¹⁸O_wwere driven by seasonally variable freshwater discharge from a subterranean aquifer beneath the island. Taken together, our results emphasize the importance of δ¹⁸O_win controlling carbonate δ¹⁸O, and suggest that typical assumptions of constant δ¹⁸O_wshould be made cautiously in nearshore settings and can contribute to less accurate reconstructions of paleotemperature. 

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4. Holocene Hydroclimatic Reorganizations in Northwest Canada Inferred From Lacustrine Carbonate Oxygen Isotopes

   https://doi.org/10.1029/2021GL092948  

   Lasher, G. Everett; Abbott, Mark B.; Anderson, Lesleigh; Yasarer, Lindsey; Rosenmeier, Michael; Finney, Bruce P. (August 2021, Geophysical Research Letters)

   Abstract Sub‐centennial oxygen (δ¹⁸O) isotopes of ostracod and authigenic calcite from Squanga Lake provides evidence of hydroclimatic extremes and a series of post‐glacial climate system reorganizations for the interior region of northwest Canada. Authigenic calciteδ¹⁸O values range from −16‰ to −21‰ and are presently similar to modern lake water and annual precipitation values. Ostracodδ¹⁸O record near identical trends with calcite, offset by +1.7 ± 0.6‰. At 11 ka BP (kaBP = thousands of years before 1950), higherδ¹⁸O values reflect decreased precipitation−evaporation (P−E) balance from residual ice sheet influences on moisture availability. A trend to lowerδ¹⁸O values until ∼8 ka BP reflects a shift to wetter conditions, and reorganization of atmospheric circulation. The last millennium and modern era are relatively dry, though not as dry as the early Holocene extreme. North Pacific climate dynamics remained an important driver of P−E balance in northwest Canada throughout the Holocene. 

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5. Influence of Recent Climate Shifts on the Relationship Between ENSO and Asian Monsoon Precipitation Oxygen Isotope Ratios

   https://doi.org/10.1029/2019JD030383  

   Cai, Zhongyin; Tian, Lide; Bowen, Gabriel J. (July 2019, Journal of Geophysical Research: Atmospheres)

   Abstract Recent studies have revealed robust in‐phase relationships between El Niño–Southern Oscillation (ENSO) and Asian Monsoon precipitation δ¹⁸O values (i.e., warm ENSO events with high δ¹⁸O values), and this relationship has been used in an attempt to reconstruct past ENSO activity. However, whether this relationship holds in the past is unknown. Here we use precipitation δ¹⁸O data from Hong Kong (East Asia) and Bangkok (Southeast Asia) and an ice core δ¹⁸O record from Dasuopu glacier (South Asia) to examine the δ¹⁸O‐ENSO relationship across two recent climate shifts that occurred during the winters of 1976/1977 and 1988/1989. On an annual scale, the δ¹⁸O‐ENSO relationship is weak prior to 1977 and strongest after 1988. We show that the changing δ¹⁸O‐ENSO relationship mainly originates from changes in the dry season isotope/climate relationship (which is significant only after 1988), whereas the rainy season relationship is relatively stable. We confirm that, consistent with earlier work on the rainy season, the significant δ¹⁸O‐ENSO relationship in the dry season post‐1988 is associated with ENSO's influence on regional convection (Bay of Bengal to South China Sea region). We suggest the insignificant dry season relationship prior to 1989 is due to limited ENSO impacts on convection in the Bay of Bengal to South China Sea region, which is supported by the insignificant relationship between ENSO and vertical velocity at 500 hPa. These findings suggest that without additional constraints, systematic variability in isotope/climate relationships will lead to large uncertainties in ENSO reconstructions based on Asian Monsoon region δ¹⁸O data. 

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