RESOLVING HIGH-RESOLUTION PALEOCLIMATE VARIABILITY FROM SUBARCTIC CANADA SPELEOTHEMS ACROSS THREE PLEISTOCENE INTERGLACIALS PERIODS (Invited Presentation)

Recent increased effort has been focused on reconstructing past climate variability, as increased variability and resulting extreme weather conditions may be more difficult for society to adapt to than disparate mean climatic states. The Pleistocene Epoch (2.5-0.117 Ma) is an ideal target for generating paleoclimate records to investigate past climate variability due to several well-constrained climate forcings and feedbacks present. Despite this, very few Pleistocene climate records exist, primarily because of geochronological dating limitations. Speleothems, however, are one type of terrestrial archive that can be dated back 600 ka (U-Th dating) or beyond (U-Pb dating). The oxygen isotopes (δ¹⁸O) of speleothem calcite is relict of former precipitation δ¹⁸O from which the calcite precipitated, and can be used to reconstruct changes in past hydroclimate. Speleothem calcite layers can also contain annual growth bands that can be analyzed to reconstruct sub-annual climate records.

In this study, we combine micro-imaging (confocal laser fluorescent microscopy; CLFM) and micro-analysis of oxygen isotopes (δ¹⁸O) on six speleothems from the subarctic region of the Northwest Territories, Canada that grew during three Pleistocene interglacial periods: Marine Isotope Stage (MIS) 11, 9, and 5. We measured 10-μm sized δ¹⁸O analyses using the Secondary Ion Mass Spectrometer (SIMS) across several fluorescent and non-fluorescent growth bands, that are perhaps annual, in each speleothem to resolve ultra-high-resolution (decadal to interannual) snapshots of climate variability during these three interglacials. Preliminary results of large-scale isotopic changes reveals that speleothem δ¹⁸O increases (by ~1.0‰ VPDB) from older to younger interglacials. This isotopic increase could be due to the temperature effect on water-calcite fractionation, as more negative δ¹⁸O values indicate warmer temperatures. The decadal to sub-annual variability of this δ¹⁸O change has yet to be analyzed but will be done by characterizing intra-band δ¹⁸O analyses within fluorescent laminations. Nonetheless, this study will be the first to produce ultra-high-resolution δ¹⁸O records from subarctic Canada to better our understanding of Northern Hemisphere Pleistocene climate variability during former Interglacial Periods.