Spatial patterns in seasonal Holocene precipitation inferred from Western Greenland lake sediments

Abstract:

As the Arctic warms, retreat of seasonal sea ice is predicted to enhance fall and winter precipitation in regions proximal to sea ice losses due to increased local evaporation. Simultaneously, northward atmospheric moisture transport is predicted to intensify, increasing summer precipitation. These mechanisms driving precipitation intensification likely have differing seasonal, spatial, and isotopic expressions, yet their long-term sensitivity to Arctic warming is poorly constrained. We present paired summer and mean annual Holocene precipitation isotope records along a north-south transect of central western Greenland between Nuuk and Ilulissat, a region spanning the seasonal sea ice front. We analyze the hydrogen isotopic composition (δ²H) of mid-chain (C₂₀, C₂₂) n-alkanoic acids, a proxy for lake water δ²H, in precipitation-fed lakes with contrasting residence times to reconstruct paired summer-biased and mean annual amount-weighted precipitation hydrogen isotopes (δ²H). We use the Environment sub-model of LakePSM, a lake proxy system model in PRYSM, to simulate the impacts of changing seasonality in precipitation amount and isotopic composition on growing season lake water δ²H. All mean annual amount-weighted lakes demonstrate decreasing δ²H from the early to mid-Holocene, suggesting increased winter precipitation through this interval. Whereas the northernmost lake rebounds to more positive δ²H in the late Holocene ca. 4 ka, δ²H of the southernmost lake declines through ca. 1.8 ka and rebounds near present. Summer-biased lakes record stable δ²H values throughout the Holocene. These records suggest strongly local changes in winter precipitation driven by sea ice retreat, in contrast to regionally-coherent signals in summer precipitation due to poleward moisture transport.