Abstract
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 ‰ (δ18Olate-Holocene > δ18Olate-glacial) to +1.7 ‰ (δ18Olate-glacial > δ18Olate-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 (δ18Olate-Holocene > δ18Olate-glacial by more than 3 ‰). Conversely, low-magnitude, positive precipitation δ18O shifts are concentrated along tropical and subtropical coasts (δ18Olate-glacial > δ18Olate-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.
Highlights
Isotopic compositions of late-glacial precipitation can be preserved in groundwaters, cave calcite, glacial ice, ground ice and lake sediments
Measured groundwater (n = 59), speleothem (n = 15) and ice core (n = 12) 18Olate-glacial values are presented in Fig. 2
Most groundwater-based late-glacial to late-Holocene shifts fall along δ2H/δ18O slopes of ∼ 8 (Fig. S58 in the Supplement), suggesting that most groundwaters record temporal shifts to precipitation isotope contents rather than to soil evaporation isotope effects
Summary
Isotopic compositions of late-glacial precipitation can be preserved in groundwaters, cave calcite, glacial ice, ground ice and lake sediments. These records have been used to better understand past climate changes for more than a half century Late-glacial ice core and ground ice records have high temporal resolution, can be analysed for 18O / 16O and 2H / 1H ratios, but are rare on non-polar lands (Dansgaard et al, 1982; Thompson et al, 1989, 1995, 1997, 1998). Some lake water proxy isotope records may be impacted by paleo-lake evaporative isotope effects that obscure the primary meteoric water signal and mask paleo-precipitation isotope compositions (e.g., lake sediment calcite, diatom silica; Leng and Marshall, 2004)
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