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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. 

Abstract High‐resolution records from past interglacial climates help constrain future responses to global warming, yet are rare. Here, we produce 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 (MIS) 11, 9, and 5e. We find 3‰ lower δ¹⁸O values during MIS 11 than MIS 5e, despite MIS 11 likely being warmer. We explore controls on high‐latitude speleothem δ¹⁸O and suggest low MIS 11 δ¹⁸O values reflect greater contribution of cold‐season precipitation to dripwater from longer annual ground thaw durations. Other potential influences include changes in precipitation source and/or increased fraction of cold‐season precipitation from diminished sea ice in MIS 11. 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.