Baffin Bay sea ice extent and synoptic moisture transport drive water vapor isotope (<i>δ</i><sup>18</sup>O, <i>δ</i><sup>2</sup>H, and deuterium excess) variability in coastal northwest Greenland

Abstract

Abstract. At Thule Air Base on the coast of Baffin Bay (76.51∘ N, 68.74∘ W), we continuously measured water vapor isotopes (δ18O, δ2H) at a high frequency (1 s−1) from August 2017 through August 2019. Our resulting record, including derived deuterium excess (dxs) values, allows an analysis of isotopic–meteorological relationships at an unprecedented level of detail and duration for high Arctic Greenland. We examine isotopic variability across multiple temporal scales from daily to interannual, revealing that isotopic values at Thule are predominantly controlled by the sea ice extent in northern Baffin Bay and the synoptic flow pattern. This relationship can be identified through its expression in the following five interacting factors: (a) local air temperature, (b) local marine moisture availability, (c) the North Atlantic Oscillation (NAO), (d) surface wind regime, and (e) land-based evaporation and sublimation. Each factor's relative importance changes based on the temporal scale and in response to seasonal shifts in Thule's environment. Winter sea ice coverage forces distant sourcing of vapor that is isotopically light from fractionation during transport, while preventing isotopic exchange with local waters. Sea ice breakup in late spring triggers a rapid isotopic change at Thule as the newly open ocean supplies warmth and moisture that has ∼10 ‰ and ∼70 ‰ higher δ18O and δ2H values, respectively, and ∼10 ‰ lower dxs values. Sea ice retreat also leads to other environmental changes, such as sea breeze development, that radically alter the nature of relationships between isotopes and many meteorological variables in summer. On synoptic timescales, enhanced southerly flow promoted by negative NAO conditions produces higher δ18O and δ2H values and lower dxs values. Diel isotopic cycles are generally very small as a result of a moderated coastal climate and the counteracting isotopic effects of the sea breeze, local evaporation, and convection. Future losses in Baffin Bay's sea ice extent will likely shift mean annual isotopic compositions toward more summer-like values, and local glacial ice could potentially preserve isotopic evidence of past reductions. These findings highlight the influence that the local environment can have on isotope dynamics and the need for dedicated, multiseason monitoring to fully understand the controls on water vapor isotope variability.

Hydroclimatic Controls on the Isotopic (δ18 O, δ2 H, d-excess) Traits of Pan-Arctic Summer Rainfall Events

“…Significant positive relations were also observed in Russia at Labytnangi (0.58 / • C, r 2 = 0.62) and Tura (0.53 / • C, r 2 = 0.57), and are similar to a regional Siberian slope of 0.50 / • C that was proposed by Kostrova et al (2020). Toolik Lake in Alaska (0.31 / relationships, albeit relatively weak, and these slopes are similar to previously reported regional values for Alaska and Greenland Bailey et al, 2018;Akers et al, 2020). Across all sites, the steepest temperature-δ 18 O slopes (between 0.93 and 0.75 / • C) were observed at the continental stations-a pattern also observed across the United States (Vachon et al, 2010;Akers et al, 2017), Europe (Rozanski et al, 1982), and Antarctica (Peel and Mulvaney, 1992).…”

“…Our data indicate that precipitation associated with these northnorthwesterly air flows were characterized by anomalously low δ 18 O and high d-excess values, such as at Thule in northwest Greenland (Figure 2). A recent study also observed a similar relation between the NAO and atmospheric water vapor isotopes measured at Thule between 2017 and 2019, whereby NAO+ circulation phases suppressed southerly flow into Thule, leading to cooler SATs and lower δ-values and higher d-excess (Akers et al, 2020). Additionally, approximately 61% of Toolik trajectories started from central Arctic regions, with precipitation characterized by anomalously low δ 18 O and high dexcess (Figure 5), with the lowest measured δ 18 O value reaching −28.5 (28 Aug) that derived from the central Arctic basin and passed over the Chukchi Sea.…”

Arctic Snow Isotope Hydrology: A Comparative Snow-Water Vapor Study

“…However, the existing models are not suited to capture key processes causing isotope evolution in Arctic seasonal snow layers: vapor diffusion from soil to snowpack, and isotope fractionation during sublimation. A way forward could be the introduction of isotope simulation routines into physically based snow models already characterizing the water fluxes (vapor flow, sublimation) and snow densification [103,107,108].…”

The Significance of Hydrogen and Oxygen Stable Isotopes in the Water Vapor Source in Dingxi Area

“…Due to the ability of stable water isotopes to characterize the origin of water [48] and to the differences in water vapor isotopic compositions from different sources, stable isotope technology has gradually become a common method for tracing water vapor sources. Investigations by some scholars have found that δ 18 O and d-excess in precipitation can be used to determine the origin of water vapor [20,23,49] Affected by various factors such as near-surface meteorological conditions, the LMWL varies from region to region. According to the least square method, the LMWL of the study area and each sampling station is obtained.…”