A Last Interglacial plant wax 2H record from the Canadian Arctic reveals the combined influences of winter moisture transport and catchment vegetation cover on paleo precipitation records

Models predict that the Arctic will experience more precipitation as temperatures rise due to anthropogenic climate change. Arctic plant communities have strong feedbacks with Arctic climate, as increased summer precipitation and higher temperatures promote the expansion of 1) Low-lying shrubs that reduce surface albedo and add water vapor to the atmosphere and 2) Wetlands that release methane, amplifying atmospheric greenhouse gas concentrations. Records of Arctic climate and plant community changes during past interglacial periods can provide insights into these feedbacks during periods of warmer-than-present conditions. In particular, lacustrine plant wax 2H records, which reflect the isotopic composition of plant source water, provide valuable information about precipitation change through time, but concurrent changes in catchment vegetation can complicate the interpretation of such records. We present an aquatic plant wax 2H record that reflects the lake water isotopic composition of Lake CF8 on Baffin Island, Nunavut, Canada to assess changes in the relative contributions of summer and winter moisture transport, with emphasis on the Last Interglacial (LIG; 129 116 ka). We interpret shifts in plant wax 2H in context of changes in the plant community inferred from pollen and sedaDNA from the same lake (Crump et al., 2021). We observe a large negative shift in plant wax 2H, coincident with both peak summer warmth (Axford et al., 2009) and a shift in vegetation from predominately forbs to dominant woody shrubs. We hypothesize that 2H-depleted plant waxes during the LIG reflects a shift in lake water isotope seasonality from summer-weighted during cooler conditions to annual-weighted during warmer conditions at Lake CF8 via the following mechanisms. First, reduced winter sea ice extent during the LIG may have caused increased 2H-depleted winter precipitation on Baffin Island. Second, an increase in plant biomass may have caused greater evapotranspiration and decreased summer runoff into Lake CF8, causing the lake water to be biased towards 2H-depleted winter precipitation (Gibson & Edwards, 2002). By interpreting lake water isotopic changes in context of paleovegetation, we attempt to resolve the influence of moisture transport patterns and vegetation community shifts on plant wax 2H at Lake CF8.