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Preprints
https://doi.org/10.5194/acp-2020-301
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-301
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 04 May 2020

Submitted as: research article | 04 May 2020

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This preprint is currently under review for the journal ACP.

Secular change in atmospheric Ar/N2 and its implications for ocean heat uptake and Brewer-Dobson circulation

Shigeyuki Ishidoya1, Satoshi Sugawara2, Yasunori Tohjima3, Daisuke Goto4, Kentaro Ishijima5, Yosuke Niwa3, Nobuyuki Aoki1, and Shohei Murayama1 Shigeyuki Ishidoya et al.
  • 1National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8569, Japan
  • 2Miyagi University of Education, Sendai 980-0845, Japan
  • 3National Institute for Environmental Studies, Tsukuba 305-8506, Japan
  • 4National Institute of Polar Research, Tokyo 190-8518, Japan
  • 5Meteorological Research Institute, Tsukuba 305-0052, Japan

Abstract. Systematic measurements of the atmospheric Ar/N2 ratio have been made at ground-based stations in Japan and Antarctica since 2012. Clear seasonal cycles of the Ar/N2 ratio with summertime maxima were found at middle to high latitude stations, with seasonal amplitudes increasing with increasing latitude. Eight years of the observed Ar/N2 ratio at Tsukuba and Hateruma, Japan showed not only secular increasing trends, but also interannual variations in phase with the observed variations in the global ocean heat content (OHC). The observed secular trend of the Ar/N2 ratio was 0.75±0.30 per meg yr-1. Sensitivity test by using a 2-dimensional model with the Brewer-Dobson circulation (BDC) scenarios indicated the possibility of the secular trend in the surface Ar/N2 ratio being modified significantly by the gravitational separation in the stratosphere. The secular trend of the Ar/N2 ratio, corrected for gravitational separation under the assumption of weakening of BDC simulated by the 2D model, was 0.60±0.30 per meg yr-1. By using a conversion factor of 3.5x10-23 per meg J-1 by assuming a 1-box ocean with a temperature of 3.5 °C, then an average OHC increase rate of 17.1±8.6 ZJ yr-1 for the period 2012–2019 was estimated from the corrected secular trend of the Ar/N2 ratio. This value is consistent with 12.2±1.2 ZJ yr-1 reported by ocean temperature measurements. The effect of the actual atmospheric circulation on the Ar/N2 ratio is still unclear, however the analytical results obtained in the present study imply that the surface Ar/N2 ratio is an important tracer for detecting spatiotemporally-integrated changes in OHC and BDC.

Shigeyuki Ishidoya et al.

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Shigeyuki Ishidoya et al.

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Short summary
The surface Ar/N2 ratio showed not only secular increasing trends, but also interannual variations in phase with the global ocean heat content (OHC). Sensitivity test by using a 2-dimensional model indicated that the secular trend in the Ar/N2 ratio being modified by the gravitational separation in the stratosphere. The analytical results imply that the surface Ar/N2 ratio is an important tracer for detecting spatiotemporally-integrated changes in OHC and stratospheric circulation.
The surface Ar/N2 ratio showed not only secular increasing trends, but also interannual...
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