Neogene paleotemperature estimates from lignin-methoxy hydrogen isotopes of sub-fossil wood in the Canadian Arctic
Neogene fossil beds in the Canadian Arctic Archipelago (CAA) provide a window into past greenhouse intervals and insights on what a future, warmer Arctic may look like. In this study, we use the hydrogen isotopes of lignin-methoxy groups (δ2HLM) from sub-fossil wood from six CAA sites (73-80°N) as a proxy for the δ2H of precipitation-derived plant water and paleotemperatures; five study sites cover Pliocene timeslices (~5.3-2.6 Ma) and the other site captures the middle Miocene (~15 Ma). Forty-three samples (all gymnosperms – Pinus, Picea and Larix spp.), each representing an individual tree, were analysed. The δ2HLM measurements were used to estimate paleo-δ2Hprecip for each site assuming the net fractionation for conifers (εLM/precip = -204 ± 12). The data reveal average precipitation during the Neogene timeslices was deuterium-enriched compared to modern precipitation (Δδ2Hprecip = +37.6 to +64.7‰ relative to modern), consistent with warmer mean paleoclimates. Assuming the modern-day δ2Hprecip-temperature sensitivity for the region (3.9‰·°C-1), the Δδ2Hprecip anomalies indicate paleotemperature anomalies (ΔT) were +9.7 to 16.7°C warmer than today. Our ΔT estimates are corroborated by independent proxy data from five sites and provide the first quantitative ΔT estimates from Prince Patrick Island (Beaufort Fm.). Our results demonstrate high potential for the δ2HLM proxy in Cenozoic paleotemperature studies and confirm the Neogene Arctic climate was dramatically warmer than today. Future research is needed to resolve the relative contributions of global versus regional boundary conditions in driving past warming in the CAA to better understand its warming potential under future greenhouse gas scenarios.