Late-glacial to late-Holocene shifts in global precipitation δ¹⁸O

Abstract. Reconstructions of Quaternary climate are often based on the isotopic content of paleo-precipitation preserved in proxy records. While many paleo-precipitation isotope records are available, few studies have synthesized these dispersed records to explore spatial patterns of late-glacial precipitation δ¹⁸O. Here we present a synthesis of 86 globally distributed groundwater (n = 59), cave calcite (n = 15) and ice core (n = 12) isotope records spanning the late-glacial (defined as ~ 50 000 to ~ 20 000 years ago) to the late-Holocene (within the past ~ 5000 years). We show that precipitation δ¹⁸O changes from the late-glacial to the late-Holocene range from −7.1 ‰ (δ¹⁸O_{late-Holocene} > δ¹⁸O_late-glacial) to +1.7 ‰ (δ¹⁸O_late-glacial > δ¹⁸O_{late-Holocene}), with the majority (77 %) of records having lower late-glacial δ¹⁸O than late-Holocene δ¹⁸O values. High-magnitude, negative precipitation δ¹⁸O shifts are common at high latitudes, high altitudes and continental interiors (δ¹⁸O_{late-Holocene} > δ¹⁸O_late-glacial by more than 3 ‰). Conversely, low-magnitude, positive precipitation δ¹⁸O shifts are concentrated along tropical and subtropical coasts (δ¹⁸O_late-glacial > δ¹⁸O_{late-Holocene} by less than 2 ‰). Broad, global patterns of late-glacial to late-Holocene precipitation δ¹⁸O shifts suggest that stronger-than-modern isotopic distillation of air masses prevailed during the late-glacial, likely impacted by larger global temperature differences between the tropics and the poles. Further, to test how well general circulation models reproduce global precipitation δ¹⁸O shifts, we compiled simulated precipitation δ¹⁸O shifts from five isotope-enabled general circulation models simulated under recent and last glacial maximum climate states. Climate simulations generally show better inter-model and model-measurement agreement in temperate regions than in the tropics, highlighting a need for further research to better understand how inter-model spread in convective rainout, seawater δ¹⁸O and glacial topography parameterizations impact simulated precipitation δ¹⁸O. Future research on paleo-precipitation δ¹⁸O records can use the global maps of measured and simulated late-glacial precipitation isotope compositions to target and prioritize field sites.