Preprints
https://doi.org/10.5194/acp-2021-787
https://doi.org/10.5194/acp-2021-787

  12 Oct 2021

12 Oct 2021

Review status: this preprint is currently under review for the journal ACP.

Spatiotemporal variations of the δ(O2/N2), CO2 and δ(APO) in the troposphere over the Western North Pacific

Shigeyuki Ishidoya1, Kazuhiro Tsuboi2, Yosuke Niwa3, Hidekazu Matsueda2, Shohei Murayama1, Kentaro Ishijima2, and Kazuyuki Saito4 Shigeyuki Ishidoya et al.
  • 1National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8569, Japan
  • 2Meteorological Research Institute, Tsukuba, Japan, Tsukuba305-0052, Japan
  • 3National Institute for Environmental Studies, Tsukuba 305-8506, Japan
  • 4Japan Meteorological Agency, Tokyo, Japan, Tokyo 105-8431, Japan

Abstract. We analyzed air samples collected onboard a cargo aircraft C-130 over the western North Pacific from May 2012 to March 2020 for atmospheric δ(O2/N2) and CO2 amount fraction. We corrected for significant artificial fractionation of O2 and N2 caused by thermal diffusion during the air sample collection by using the simultaneously-measured δ(Ar/N2). The observed seasonal cycles of the δ(O2/N2) and atmospheric potential oxygen (δ(APO)) varied nearly in opposite phase to that of the CO2 amount fraction at all latitudes and altitudes. Seasonal amplitudes of δ(APO) decreased with latitude from 34 to 25° N, as well as with increasing altitude from the surface to 6 km by 50–70 %, while those of CO2 amount fraction decreased by less than 20 %. By comparing the observed values with the simulated δ(APO) and CO2 amount fraction values generated by an atmospheric transport model, we found that the seasonal δ(APO) cycle in the middle troposphere was modified significantly by a superposition of the northern and southern hemispheric seasonal cycles due to the inter-hemispheric mixing of air. The simulated δ(APO) underestimated the observed interannual variation in δ(APO) significantly, probably due to the interannual variation in the annual mean air-sea O2 flux. Interannual variation in δ(APO) driven by the net marine biological activities, obtained by subtracting the assumed solubility-driven component of δ(APO) from the total variation, indicated a clear evidence of influence on annual sea-to-air (air-to-sea) marine biological O2 flux during El Niño (La Niña). By analyzing the observed secular trends of δ(O2/N2) and CO2 amount fraction, global average terrestrial biospheric and oceanic CO2 uptakes for the period 2012–2019 were estimated to be (1.8 ± 0.9) and (2.8 ± 0.6) Pg a−1 (C equivalents), respectively.

Shigeyuki Ishidoya et al.

Status: open (until 23 Nov 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Shigeyuki Ishidoya et al.

Shigeyuki Ishidoya et al.

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Short summary
Atmospheric O2/N2 ratio and CO2 concentration over the western North Pacific are presented. We found significant modification of the seasonal APO cycle in the middle troposphere due to the inter-hemispheric mixing of air. APO driven by the net marine biological activities indicated annual sea-to-air O2 flux during El Niño. Terrestrial biospheric and oceanic CO2 uptakes during 2012–2019 were estimated to be 1.8 and 2.8 PgC/yr, respectively.
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