Ice Core 17 O Reveals Past Changes in Surface Air Temperatures and Stratosphere to Troposphere Mass Exchange

• Published in: Atmosphere
• Main Authors: Pradeep K. Aggarwal, Frederick J. Longstaffe, Franklin W. Schwartz
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2023
• Subjects: isotope; oxygen-17; ice core; climate change; paleothermometry; stratosphere; Meteorology. Climatology; QC851-999; Antarctic; Greenland; Antarc*; Greenland ice cores
• Online Access: https://doi.org/10.3390/atmos14081268; https://doaj.org/article/ded090c651c3494ea6fc84da3c812995

In this study, we have investigated the oxygen isotope compositions (δ 17 O and δ 18 O) of modern rain and ice cores using published isotopic data. We find that, contrary to existing interpretations, precipitation δ 17 O is influenced by two factors: mass-dependent fractionation (MDF), which occurs during ocean evaporation, and mass-independent fractionation (MIF), which happens in the stratosphere. The MDF contribution remains constant and can be understood by studying tropical rain, as the overall movement of mass in the tropics is upward toward the stratosphere. On the other hand, the MIF effect comes from the mixing of stratospheric air in the troposphere, which is a result of the Brewer–Dobson circulation. This MIF effect on precipitation 17 O increases from the tropics toward the poles and is observed consistently in modern precipitation and ice cores. The relative δ 17 O and δ 18 O composition, denoted as ∆‘ 17 O, in modern precipitation can be calibrated with surface air temperature, creating a new and independent tool for estimating past temperatures. We used this calibration along with the ∆‘ 17 O of Antarctic and Greenland ice cores, and our reconstructed past temperatures are in excellent agreement with those derived from borehole thermometry or gas phase analysis of air trapped in the ice. The ∆‘ 17 O method overcomes the problems associated with using δ 18 O alone for paleothermometry. Our findings align with climate models that suggest a weakening of the Brewer–Dobson circulation during the Last Glacial Maximum. Furthermore, our approach could be used to monitor future changes in stratosphere–troposphere mass exchange in response to a warming climate caused by increasing greenhouse gases.