Seasonal Variations in Moisture Origin Explain Spatial Contrast in Precipitation Isotope Seasonality on Coastal Western Greenland

Increased precipitation in the Arctic is a robust feature across model simulations of the coming century, driven by intensification of meridional moisture transport and enhanced local evaporation in the absence of sea ice. These mechanisms are associated with distinct, seasonal, spatial, and, likely, precipitation isotope (delta H-2(Precip)) expressions. Historical observations of delta H-2(Precip) reveal a contrast in seasonality between southwestern and northwestern coastal Greenland: delta H-2(Precip) in northwestern Greenland varies in phase with local temperature, whereas delta H-2(Precip) in southwestern Greenland is decoupled from local temperature and exhibits little seasonal variation. We test the hypothesis that reduced delta H-2(Precip) seasonality in southwestern Greenland relative to northwestern Greenland results from dynamic moisture source variations, by diagnosing monthly average moisture sources to three sink regions (Kangilinnguit, Ilulissat, and Qaanaaq) using the Water Accounting Model-2layers model. All domains demonstrate strong intra-annual moisture source variations. Moisture to the southernmost region is sourced most remotely in summer and most locally in winter, associated with stronger cooling from the source in summer than winter, promoting more negative delta H-2(Precip) and counteracting local temperature-driven seasonality. In comparison, moisture transport distance to the northernmost region is relatively constant, as local sea ice restricts northward migration of the winter moisture source. We simulate seasonal patterns in delta H-2(Precip) in a simple Rayleigh model, which confirm the importance of source temperature and starting isotopic compositions in determining delta H-2(Precip) for these regions. delta H-2(Precip) sensitivity to moisture source variability suggests these coastal Arctic settings may yield paleoclimate records sensitive to the moisture transport processes predicted to amplify future precipitation.

Automated summary

Increased precipitation in the Arctic in the coming century is driven by moisture transport and local evaporation, leading to various expressions in isotopic patterns. Historical observations in Greenland show differences in seasonal patterns between the southwest and northwest coast, potentially due to dynamic moisture source variations. The sensitivity of precipitation isotopes to moisture source variability suggests that coastal Arctic regions may provide valuable paleoclimate records.