Aggarwal, P.K.; Longstaffe, F.J.; Schwartz, F.W. Ice Core 17O Reveals Past Changes in Surface Air Temperatures and Stratosphere to Troposphere Mass Exchange. Atmosphere2023, 14, 1268.
Aggarwal, P.K.; Longstaffe, F.J.; Schwartz, F.W. Ice Core 17O Reveals Past Changes in Surface Air Temperatures and Stratosphere to Troposphere Mass Exchange. Atmosphere 2023, 14, 1268.
Aggarwal, P.K.; Longstaffe, F.J.; Schwartz, F.W. Ice Core 17O Reveals Past Changes in Surface Air Temperatures and Stratosphere to Troposphere Mass Exchange. Atmosphere2023, 14, 1268.
Aggarwal, P.K.; Longstaffe, F.J.; Schwartz, F.W. Ice Core 17O Reveals Past Changes in Surface Air Temperatures and Stratosphere to Troposphere Mass Exchange. Atmosphere 2023, 14, 1268.
Abstract
Oxygen and hydrogen isotopes (18O and 2H) in polar ice offer strong evidence of both long-term and abrupt climate changes. However, reliably estimating surface air temperatures from past climates has proven difficult because the relationship between 18O and temperature cannot be calibrated. In this study, we investigated the 17O and 18O of modern rain and ice cores using published data. We found that precipitation 17O is influenced by two factors: mass-dependent fractionation (MDF) that occurs during ocean evaporation, and mass-independent fractionation (MIF) that happens in the stratosphere. The MDF contribution remains constant and can be understood from studying tropical rain, as the overall movement of mass in the tropics is upward towards 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 17O increases from the tropics towards the poles. Therefore, the relative 17O and 18O composition, denoted as '17O, in modern precipitation can be calibrated with surface air temperature, creating a new, independent tool for estimating past temperatures. We used this calibration along with '17O of Antarctic and Greenland ice cores and our results for past temperatures are in excellent agreement with those from borehole thermometry or gas phase analysis of air trapped in the ice. The 17O method overcomes the problems associated with using 18O for paleothermometry. Our findings align with climate models that suggest a weakening of the Brewer-Dobson circulation during the Last Glacial Maximum. Furthermore, our method could be used to monitor future changes in response to a warming climate caused by increasing greenhouse gases.
Environmental and Earth Sciences, Atmospheric Science and Meteorology
Copyright:
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