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

Abstract

AbstractHydrogen (δD) and oxygen (δ18O) isotopic ratios are strongly correlated in precipitation over time and space, defining the meteoric water line, and the slope of this δD‐δ18O relationship reflects covariations of deuterium excess (d‐excess) with δD or δ18O. This δD‐δ18O line provides a tool for inferring hydrologic processes from the evaporation source to condensation site. Here, we present δD‐δ18O relationships on seasonal and annual timescales for daily precipitation, snow pits, and a 15‐m ice core (Owen) at Summit, Greenland. Seasonally, precipitation δD‐δ18O 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‐δ18O 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‐δ18O line slopes are significantly related to these indices, demonstrating that these factors are recorded in ice cores.