Preprints
https://doi.org/10.5194/cp-2019-74
https://doi.org/10.5194/cp-2019-74

  02 Jul 2019

02 Jul 2019

Review status: this preprint was under review for the journal CP but the revision was not accepted.

Precipitation and ice core δD-δ18O line slopes and their climatological significance

Ben G. Kopec1,2, Xiahong Feng2, Erich C. Osterberg2, and Eric S. Posmentier2 Ben G. Kopec et al.
  • 1Department of Geology, Gustavus Adolphus College, St. Peter, MN, 56082, USA
  • 2Department of Earth Sciences, Dartmouth College, Hanover, NH, 03755, USA

Abstract. The meteoric water line, defined by the correlation of hydrogen (δD) and oxygen (δ18O) values, is one of the earliest described characteristics of precipitation isotopic variations. However, spatial and temporal variations in the slope of this line are less studied. The slope of the δD-δ18O relationship is coupled with how d-excess covaries with δD or δ18O, and may provide an integrated tool for inferring hydrologic processes from the evaporation to condensation site. We present a study of δD-δ18O relationships on seasonal and annual timescales for event-based precipitation and a 15-meter ice core (Owen) at Summit, Greenland. Seasonally, precipitation δD-δ18O slopes are less than eight (summer = 7.71; winter = 7.77), while the annual slope is greater than eight (8.27). We suggest intra-season slopes result primarily from Rayleigh distillation, which, under prevailing conditions, produces slopes less than eight. 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 to contributions of vapor sublimated from the Greenland Ice Sheet. Higher sublimated moisture proportions in summer cause larger separations between seasonal δD-δ18O lines, and thus higher annual slopes. Intra-seasonal distributions of precipitation amount also influence annual slopes because slopes are weighed by the number of storms each season. We generate indices to quantify sublimation proportion (SPI) and precipitation distribution (PDI), and find that annual Owen core slope measurements are significantly related to these indices, demonstrating that sublimation and precipitation distribution represent important climate conditions recorded in ice cores.

Ben G. Kopec et al.

 
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Ben G. Kopec et al.

Data sets

Hydrogen and oxygen isotope ratio measurements for 15 meter Owen Ice Core, Summit, Greenland, 1977-2010 B. Kopec, X. Feng, E. Osterberg, and E. Posmentier https://doi.org/10.18739/A21J9774C

Ben G. Kopec et al.

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Short summary
We present water isotope measurements in precipitation and a shallow ice core from Summit, Greenland. We use an underutilized approach by observing the relationship between hydrogen and oxygen isotope ratios to investigate controls of Greenland precipitation. Our results suggest that sublimation from the ice sheet is a significant moisture source for Summit precipitation, which has implications for interpreting ice core records and understanding ice sheet mass balance due to moisture recycling.