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

• Published in: Atmospheric Chemistry and Physics
• Main Authors: P. D. Akers, B. G. Kopec, K. S. Mattingly, E. S. Klein, D. Causey, J. M. Welker
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2020
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Arctic; Baffin Bay; Greenland; Thule Air Base; Baffin; North Atlantic; North Atlantic oscillation; Sea ice; Thule Air; Thule
• Online Access: https://doi.org/10.5194/acp-20-13929-2020; https://doaj.org/article/dc3e1be33fef4f7cadf0697f8aa28385

At Thule Air Base on the coast of Baffin Bay (76.51 ∘ N, 68.74 ∘ W), we continuously measured water vapor isotopes ( δ 18 O , δ 2 H ) 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 δ 18 O and δ 2 H 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 δ 18 O and δ 2 H 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 ...