A local meteoric water line for interior Alaska constrains paleoclimate from 40 000 year old relict permafrost

Abstract Anthropogenic climate warming is degrading permafrost across interior Alaska. Information from past warming events provides long-term perspectives for future trajectories; however, late Quaternary seasonal temperatures are poorly constrained. We have established a stable water isotope meteoric water line for interior Alaska and measured stable water isotope values from 126 permafrost cores representing different ice types deposited over the past ∼40 ka (thousand years before 1950 CE). Samples represent two late Quaternary warm periods: marine isotope stage three (MIS3; 57–29 ka) and the Holocene (11.7 ka-present). Older samples provide insight into local climatic conditions slightly before the first archeological evidence for Paleolithic hunter-gatherers in the region. From permafrost ice we calculate that summer temperatures warmed by ∼10 °C between late MIS3 and today, with six degrees of warming between 40–30 ka and 3 ka and an additional 4 °C of warming since 3 ka. Half this recent 4 °C warming has occurred over the past 70 years.