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

Abstract

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 (δ2HPrecip) expressions. Historical observations of δ2HPrecip reveal a contrast in seasonality between southwestern and northwestern coastal Greenland: δ2HPrecip in northwestern Greenland varies in phase with local temperature, whereas δ2HPrecip in southwestern Greenland is decoupled from local temperature and exhibits little seasonal variation. We test the hypothesis that reduced δ2HPrecip 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 δ2HPrecip 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 δ2HPrecip in a simple Rayleigh model, which confirm the importance of source temperature and starting isotopic compositions in determining δ2HPrecip for these regions. δ2HPrecip 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.

Southern Baffin Island mean annual precipitation isotopes modulated by summer and autumn moisture source changes during the past 5800 years

“…Therefore, increases in local moisture contributions, which primarily occur in the late autumn and early winter due to enhanced evaporation from warmer and/or newly ice‐free seas (Bintanja and Selten, 2014), would probably cause mean annual precipitation isotope values to become relatively 2 H‐enriched. As the Labrador Sea is probably an important moisture source to southern Baffin Island (Nusbaumer et al ., 2019; Cluett et al ., 2021), decreased autumn and winter sea ice extent and/or duration in the Labrador Sea may open up a local moisture source, which in turn would cause relatively 2 H‐enriched precipitation to drop in the winter, causing amount‐weighted mean annual precipitation isotopes to become more 2 H‐enriched.…”

“…Although 70% of annual precipitation at Lake QPT falls in the summer and autumn, we might expect changes in winter precipitation to have the greatest impact on mean annual precipitation isotopes, as changes in distal moisture transport in the summer do not greatly impact precipitation isotopes (Cluett et al ., 2021). Since autumn and winter precipitation isotopes can be influenced by seasonal sea ice duration and extent as well as by source region temperature, we compare Lake QPT C 22 n ‐alkanoic acid δ 2 H data with a sea ice and sea surface temperature record from Site CC04 near the modern limit of winter sea ice in the northern Labrador Sea (Gibb et al ., 2015, Figs.…”

“…Low‐elevation Arctic regions are growing in importance for paleoclimate research as isotope and geochemical proxies are developed and deployed in lacustrine, paleosol and coastal marine archives (Konecky et al ., 2020). Moisture source and isotope modeling for coastal western Greenland suggests that precipitation isotopes in these regions are sensitive to changes in moisture source and to local temperature (Cluett et al ., 2021). Proxy records in these regions can therefore be useful to describe changes in moisture sources associated with seasonal and long‐term global climate changes, as described above.…”

Western Siberia experienced rapid shifts in moisture source and summer water balance during the last deglaciation and early Holocene

“…Precipitation hydrogen isotopes in turn reflect a variety of climate signals including the isotope value of the evaporation source, moisture transport distance and local condensation temperature (Dansgaard, 1964). Source conditions tend to be important for the isotope value of precipitation that travels short distances to the site of precipitation, whereas the source‐to‐sink temperature gradient exerts a larger control on precipitation that travels long distances (Putman et al ., 2017; Cluett et al ., 2021) Furthermore, aquatic and terrestrial plants draw on different pools of water in their environments: lake water and soil moisture, respectively. Terrestrial plants in general produce longer chain‐length waxes than aquatic plants (Sachse et al ., 2012; Thomas et al ., 2016; Dion‐Kirschner et al ., 2020).…”

“…In addition, summer evapotranspiration further reduces distillation along the transport path (Salati et al ., 1979; Gat and Matsui, 1991; Victoria et al ., 1991; Bonne et al ., 2020). Summer precipitation δ 2 H values in Siberia are less sensitive to temperature than to moisture recycling and source isotope value (Kurita et al ., 2004), similar to the mechanisms controlling precipitation isotopes elsewhere in the Arctic (Cluett et al ., 2021).…”