Oxygen anomaly in near surface carbon dioxide reveals deep stratospheric intrusion

Abstract

Stratosphere-troposphere exchange could be enhanced by tropopause folding, linked to variability in the subtropical jet stream. Relevant to tropospheric biogeochemistry is irreversible transport from the stratosphere, associated with deep intrusions. Here, oxygen anomalies in near surface air CO2 are used to study the irreversible transport from the stratosphere, where the triple oxygen isotopes of CO2 are distinct from those originating from the Earth’s surface. We show that the oxygen anomaly in CO2 is observable at sea level and the magnitude of the signal increases during the course of our sampling period (September 2013-February 2014), concordant with the strengthening of the subtropical jet system and the East Asia winter monsoon. The trend of the anomaly is found to be 0.1‰/month (R2 = 0.6) during the jet development period in October. Implications for utilizing the oxygen anomaly in CO2 for CO2 biogeochemical cycle study and stratospheric intrusion flux at the surface are discussed.

Spatiotemporal Variability of Oxygen Isotope Anomaly in near Surface Air CO2 over Urban, Semi-Urban and Ocean Areas in and around Taiwan

“…This value of λ o is chosen because it corresponds to the fractionation that occurs in transpiration (Landais et al, 2006) at an average relative humidity of 75% (more details about the choice of λ values are given in the Supplementary Material). With this selection of λ, the formulation of the partitioning of the tripleoxygen isotopes of CO 2 coming from exchanges with diverse waters (meteoric, vapor, soil, stem, and leaf) can be simplified since the triple isotope variations in these processes have similar λ values as λ o (Landais et al, 2006;Liang and Mahata, 2015). As a result, the oxygen isotope anomaly as defined below remains unchanged despite isotopic fractionation associated with oxygen transfer.…”

“…O value of a sample of CO 2 was ~0.01‰ (1-σ standard deviation), and the accuracy was also ~0.01‰ (see Liang and Mahata, 2015;Mahata et al, 2016). The uncertainty in δ O analysis) were 0.06‰ (e.g., see Liang and Mahata, 2015;.…”

“…where the δ-values (and ∆ 17 O values), the isotopic composition of oxygen in CO 2 (or O 2 when referring to atmospheric O 2 ), are expressed in ‰ relative to V-SMOW, following the same definition as Liang and Mahata (2015). Note that we choose value of λ to be 0.516 in Eq.…”

Near Surface CO2 Triple Oxygen Isotope Composition

“…In summer and fall Taiwan is significantly affected by typhoons, making the weather more dynamic and highly turbulent. All of these meteorological conditions make this region a possible site for stratospheric air incursion down to ground and sea levels (Liang and Mahata 2015). The Taipei basin has a particularly shallow boundary mixed layer in the winter (~500 m in daytime) (Chou et al 2007) which is generally lower than the surrounding mountains (~1000 m to the north and southeast), making the air mass confined and isolated in the basin for about a week.…”

“…The results from a phase correlation study of O 3 and CO supported this conclusion and suggested that the stratosphere-troposphere exchange carries stratospheric air into the troposphere at select places (Liang et al 2008b). This would be especially important in regions where intrusion events like typhoons/monsoons occur frequently (such as Taiwan), and the magnitude of the anomaly could be enhanced during those episodes (Liang and Mahata 2015).…”