Revisiting the origin of Greenland moisture sources: Regional differences, seasonality and land/ocean sources

Abstract:

Ice cores provide unique information about past climate changes. The interpretation of the isotope signal relies strongly on the knowledge on the underlying moisture transport and variability hereof. Knowledge about the moisture source and conditions during transport are all essential for describing the amount of distillation that an airmass experience on the way to the polar ice sheet and is thus relevant for ice core climate interpretation.

This study identifies moisture sources for Greenland ice core sites using a combination of backward trajectories and moisture source diagnostics. Using the Lagrangian moisture source diagnostic WaterSip, based on a global transport climatology calculated with the FLEXPART model, and spanning the entire ERA-Interim dataset, we identify Greenland moisture sources for present-day conditions (1980-2017). We focus on selected deep ice core sites and identify the key moisture source areas and their patterns of variability. The role of land vs. ocean moisture sources are investigated, with a particular focus on land sources from North America and Greenland.

Results show that the ice core sites have different spatial patterns of moisture sources. Summer and winter moisture uptake regions are not the same for most cores. The moisture sources are shifted westwards and north with larger amount of land uptakes. During summer, land sources from North America and Greenland contribute with significant amount (40-70%) to the total moisture uptake budget for all cores. It is suggested that the shift in land and ocean sources is a result of seasonal differences in atmospheric circulation features thus changing the relative importance of land and ocean sources.

Overall this analysis highlight the complexity of moisture sources variability and their drivers. For each ice core site differences exists in both the seasonality of the precipitation, variability of the source regions as well as variability in transport patterns and transport conditions. This contributes to the understanding of which ice cores are comparable and which represents information about unique climate signals such as sea ice and sea surface variability.