Climatological Significance of δD‐δ¹⁸O Line Slopes From Precipitation, Snow Pits, and Ice Cores at Summit, Greenland

Abstract

Abstract Hydrogen (δD) and oxygen (δ 18 O) isotopic ratios are strongly correlated in precipitation over time and space, defining the meteoric water line, and the slope of this δD‐δ 18 O relationship reflects covariations of deuterium excess (d‐excess) with δD or δ 18 O. This δD‐δ 18 O line provides a tool for inferring hydrologic processes from the evaporation source to condensation site. Here, we present δD‐δ 18 O relationships on seasonal and annual timescales for daily precipitation, snow pits, and a 15‐m ice core (Owen) at Summit, Greenland. Seasonally, precipitation δD‐δ 18 O slopes are less than 8 (summer = 7.70; winter = 7.77), while the annual slope is greater than 8 (8.27). We suggest that intra‐season slopes result primarily from Rayleigh distillation, which, under prevailing conditions, produces slopes less than 8. The summer line has a greater intercept (higher d‐excess) than the winter line. This separation causes annual slopes to be greater than seasonal ones. We attribute high summer d‐excess primarily to contributions of vapor sublimated from the Greenland Ice Sheet and other terrestrial sources. High sublimated moisture proportions result in a large separation between seasonal δD‐δ 18 O lines, and thus high annual slopes. Inter‐seasonal weighting of precipitation amount also influences annual slopes because slopes are weighed by the number of storms each season. Using snow pit measurements, we demonstrate that precipitation isotopic signals translate to the snowpack. We generate indices to determine Sublimation Proportion Index and Precipitation Weighting Index, and find that annual Owen core δD‐δ 18 O line slopes are significantly related to these indices, demonstrating that these factors are recorded in ice cores.