Effects of Ozone Isotopologue Formation on the Clumped‐Isotope Composition of Atmospheric O₂

Abstract

Odd oxygen (O[ 3 P], O[ 1 D], and O 3 ) is a key component of the atmosphere's oxidizing capacity. As such, tracing its evolution over time may provide better constraints on greenhouse-gas lifetimes, stratosphere-troposphere coupling, biosphere-atmosphere interactions, and radiative forcing in the past. Moreover, elevated odd-oxygen concentrations in the upper troposphere and stratosphere mean that a globally integrated record of odd-oxygen chemistry would be a unique window on the high-altitude atmosphere of the past, not just in terms of chemistry but also climate (

Clumped‐Isotope Constraint on Upper‐Tropospheric Cooling During the Last Glacial Maximum

“…In both schemes, atomic oxygen ([O( 3 P )]) concentration and local temperature are the primary drivers of the instantaneous rates of isotope exchange. The pressure‐dependent scheme reproduces modern observations quantitatively across latitudes, years, and seasons (Yeung et al., 2021), so those results are reported in the main text. The results of the pressure‐independent calculation of Δ 36 values are shown in Tables S1 and S2 in Supporting Information ; the simulated Δ 36 differences between the time periods of interest are nearly identical, despite the absolute magnitude of Δ 36 values being different.…”

“…Specifically, the modeled LGM-to-PI change ranges from −0.05‰ to −0.08‰, while the modeled PI-to-PD change is −0.04‰ and −0.06‰ for high-and low-fire scenarios, respectively (Table S2 in Supporting Information S1 and Figure 4). Modeled variations in global-mean surface Δ 36 values benefit from a cancellation of systematic errors (Yeung et al, 2021), resulting in higher expected accuracy for changes in Δ 36 values between LGM, PI, and PD scenarios. The high-fire emissions scenarios yield modeled Δ 36 changes in better agreement with those measured in ice cores; low-fire model scenarios yield larger Δ 36 changes, with pronounced disagreements with observations when comparing changes against the PD.…”

“…Similar to previous work (Yeung et al., 2021), two online Δ 36 calculation schemes (pressure‐independent and pressure‐dependent) were implemented in GEOS‐Chem to assess the sensitivity of the model results to Δ 36 parameterization. In the pressure‐independent scheme, atmospheric Δ 36 values trend toward isotopic equilibrium according to the local kinetics of oxygen isotope exchange.…”

“…To attribute changes in the tropospheric Δ 36 value to upper-tropospheric temperature, tropospheric O 3 , and stratosphere-troposphere exchange, we use a two-box model approach described by the equation (Yeung et al, 2021): The inferred values of each variable in Equation 4 can be found in Table 1. We find that the Δ 36,t decrease accounts for roughly half (46%-65%) of the LGM-to-PI change in Δ 36,trop value in the model, with high-fire scenarios on the lower end of the range.…”

Retrieving a “Weather Balloon” From the Last Ice Age

“…To provide a sense of the challenge of these measurements, consider that the abundance of 36 O 2 relative to 32 O 2 increases by only ∼13 ppm per degree of cooling (i.e., ∼0.013‰ K −1 ; Yeung et al., 2021). So, the authors' task at hand was to resolve order‐ppm changes in the abundance of something that itself only occurs at the ppm level.…”