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Discussion papers
https://doi.org/10.5194/acp-2019-69
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-69
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 25 Feb 2019

Research article | 25 Feb 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Global carbon budgets estimated from atmospheric O2/N2 and CO2 observations in the western Pacific region over a 15-year period

Yasunori Tohjima, Hitoshi Mukai, Toshinobu Machida, Yu Hoshina, and Shin-Ichiro Nakaoka Yasunori Tohjima et al.
  • National Institute for Environmental Studies, Tsukuba, 305-8506, Japan

Abstract. Time series of atmospheric O2/N2 ratio and CO2 mole fraction of flask samples obtained from NIES’s flask sampling network are presented. The network includes two ground sites, Hateruma Island (HAT, 24.05 °N, 123.81 °E) and Cape Ochiishi (COI, 43.17 °N, 145.50 °E), and cargo ships regularly sailing in the western Pacific. Based on temporal changes in fossil fuel-derived CO2 emissions, global atmospheric CO2 burden, and atmospheric potential oxygen (APO), which were calculated from the observed O2/N2 ratio and CO2 mole fraction according to APO = O2 + 1.1 × CO2, we estimated the global carbon sinks of the ocean and land biosphere for a period of more than 15 years. In this carbon budget calculation, we adopted a correction for the time-varying ocean O2 outgassing effect with an average of 0.43 PgC yr−1 for 2000–2016. The outgassing effect, attributed to global ocean warming, was evaluated under the assumption that the net ocean gas flux is proportional to the change in the ocean heat content for the 0–2000 m layer. The resulting oceanic and land biotic carbon sinks were 2.5 ± 0.6 PgC yr−1 and 1.6 ± 0.8 PgC yr−1, respectively, for a 17-year period (2000–2016) and 2.3 ± 0.6 PgC yr−1 and 2.0 ± 0.8 PgC yr−1, respectively, for a 14-year period (2003–2016). Despite the independent approaches, these sink values of this study agreed with those estimated by the Global Carbon Project (GCP) within a difference of about ±0.3 PgC yr−1. We examined the carbon sinks for an interval of five years to assess the temporal trends. The pentad (5-year) ocean sinks showed an increasing trend at a rate of 0.09 ± 0.02 PgC yr−2 during 2001–2014, while the pentad land sinks showed an increasing trend at a rate of 0.23 ± 0.03 PgC yr−2 for 2001–2009 and a decreasing trend at a rate of − 0.23 ± 0.05 PgC yr−2 during 2009–2014. Although there is good agreement in the trends of the pentad sinks between this study and that of GCP, the increasing rate of the pentad ocean sinks of this study was about two times larger than that of GCP.

Yasunori Tohjima et al.
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Yasunori Tohjima et al.
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Short summary
How much fossil fuel-derived carbon dioxide was taken up by land biosphere and ocean, respectively, was evaluated from atmospheric carbon dioxide and oxygen observations in the western Pacific over a 15-year period. The results showed that about 30 % and 18 % of the fossil fuel-derived carbon dioxide emitted during a 17-year period (2000–2016) were taken up by the ocean and land sinks, respectively. Long-term trends of land and ocean sinks for the decadal period were also evaluated.
How much fossil fuel-derived carbon dioxide was taken up by land biosphere and ocean,...
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