NOAA/WDS Paleoclimatology - Guliya Ice Cap, China, -0.64 to 15ka BP Ice Core d18O and d-excess Data

Ice cores from the northwestern Tibetan Plateau (NWTP) contain long records of regional climate variability, but refrozen meltwater and dust in these cores has hampered development of robust timescales. Here we introduce an approach to dating the ice via the isotopic composition of atmospheric O2 in air bubbles (d18Oatm), along with annual layer counting and radiocarbon dating. We provide a robust chronology for water isotope records (d18Oice and d-excess) from three ice cores from the Guliya ice cap in the NWTP. The measurement of d18Oatm, although common in polar ice core timescales, has rarely been used on ice cores from low- latitude high-altitude glaciers due to 1) low air pressure, 2) the common presence of refrozen melt that adds dissolved gases and reduces the amount of air available for analysis, and 3) the respiratory consumption of molecular oxygen (O2) by microorganisms in the ice, which fractionates the d18O of O2 from the atmospheric value. Here we make corrections for melt and respiration to address these complications. The resulting records of water isotopes from the Guliya ice cores reveal climatic variations over the last 15,000 y, the timings of which correspond to those observed in independently dated lake and speleothem records and confirm that the Guliya ice cap existed before the Holocene. The millennial-scale drivers of d18Oice are complex and temporally variable; however, Guliya d18Oice values since the mid-20th century are the highest since the beginning of the Holocene and have increased with regional air temperature.