Climatological Significance of delta D-delta O-18 Line Slopes From Precipitation, Snow Pits, and Ice Cores at Summit, Greenland

Hydrogen (delta D) and oxygen (delta O-18) isotopic ratios are strongly correlated in precipitation over time and space, defining the meteoric water line, and the slope of this delta D-delta O-18 relationship reflects covariations of deuterium excess (d-excess) with delta D or delta O-18. This delta D-delta O-18 line provides a tool for inferring hydrologic processes from the evaporation source to condensation site. Here, we present delta D-delta O-18 relationships on seasonal and annual timescales for daily precipitation, snow pits, and a 15-m ice core (Owen) at Summit, Greenland. Seasonally, precipitation delta D-delta O-18 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 delta D-delta O-18 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 delta D-delta O-18 line slopes are significantly related to these indices, demonstrating that these factors are recorded in ice cores. Plain Language Summary We present water isotope measurements in precipitation, snow pits, and a shallow ice core from Summit, Greenland. We investigate the relationship between hydrogen and oxygen isotope ratios, emphasizing the temporal variation in the slope of the local meteoric water line and its relationship with climate conditions. We demonstrate that, on the annual scale, variations in the hydrogen (delta D) versus oxygen (delta O-18) isotopic ratio slope is significantly controlled by moisture contribution from sublimation off the Greenland Ice Sheet and by variations in the seasonal weighting of precipitation. We demonstrate that these isotopic signals of precipitation translate directly to the snowpack and thus are potentially transferred to ice cores. We obtained annual delta D- versus delta O-18 slopes from a 32-year ice core and show that the slope variations are related to the relative amount of sublimation and seasonal weighting of the precipitation. These results open a new way of interpreting ice cores for their climatic significance. The work may also help better understand ice sheet mass balance through the quantification of sublimation-sourced precipitation.