Arctic Cyclone Water Vapor Isotope Ratios Support Past Sea Ice Retreat Recorded in Greenland Ice Sheet

Rapid warming in the Arctic is associated with important changes to the Arctic water cycle: loss of sea ice, increasing atmospheric humidity, permafrost thaw, and water-induced ecosystem changes. Understanding these complex modern processes is critical to interpreting past hydrologic changes preserved in paleoclimate records and assessing future Arctic changes. Cyclones are a prevalent feature of the Arctic and water vapor isotope ratios during these events provide insights into modern hydrologic processes that help explain past changes to the Arctic water cycle. Here we present continuous measurements of water vapor isotope ratios (δ18O, δ2H, d-excess) in northern Alaska from a 2013 Arctic cyclone event. This cyclone resulted in a sharp d-excess decrease and disproportional δ18O enrichment, indicative of an open Arctic Ocean water vapor source with higher humidity. Past transitions to warmer climates inferred from Greenland ice core records also reveal sharp decreases in d-excess values, hypothesized to represent reduced sea ice extent and an increase in oceanic moisture source to Greenland Ice Sheet precipitation. Thus, measurements of water vapor isotope ratios during an Arctic cyclone provide a critical processed-based explanation, and the first direct confirmation, of relationships previously assumed to govern water isotope ratios during sea ice retreat and increased input of northern ocean moisture into the Arctic water cycle.