Abstract
The measurement of atmospheric O2 concentrations and related oxygen budget have been used to estimate terrestrial and oceanic carbon uptake. However, a discrepancy remains in assessments of O2 exchange between ocean and atmosphere (i.e. air-sea O2 flux), which is one of the major contributors to uncertainties in the O2-based estimations of the carbon uptake. Here, we explore the variability of air-sea O2 flux with the use of outputs from Coupled Model Intercomparison Project phase 6 (CMIP6). The simulated air-sea O2 flux exhibits an obvious warming-induced upward trend (∼1.49 Tmol yr−2) since the mid-1980s, accompanied by a strong decadal variability dominated by oceanic climate modes. We subsequently revise the O2-based carbon uptakes in response to this changing air-sea O2 flux. Our results show that, for the 1990–2000 period, the averaged net ocean and land sinks are 2.10±0.43 and 1.14±0.52 GtC yr−1 respectively, overall consistent with estimates derived by the Global Carbon Project (GCP). An enhanced carbon uptake is found in both land and ocean after year 2000, reflecting the modification of carbon cycle under human activities. Results derived from CMIP5 simulations also investigated in the study allow for comparisons from which we can see the vital importance of oxygen dataset on carbon uptake estimations.
摘要
目前对大气氧浓度及相关氧收支的估算已经被用于反推海洋和陆地的碳汇。然而,在这种基于氧的碳汇估计方法中,如何衡量海气之间氧通量至今仍存在着较大的分歧,这已经成为了影响碳汇估算的主要不确定因素之一。在这种背景下,本文利用国际耦合模式比较计划第六阶段(CMIP6)的模式数据探索了海气间氧通量的时空变率。结果表明,从19世纪80年代中期开始,全球海气氧通量呈现出了非常明显的上升趋势(约1.49 Tmol yr-2)。这种增暖导致的上升趋势与海洋气候模态主导的年代际振荡共同作用,最终形成了海气氧通量的时间变化序列。我们根据上述结果,对基于氧收支的海洋和陆地的碳汇估算进行了订正:在1900--2000年期间,海洋和陆地的平均碳沉降速率分别为2.10±0.43 Gt C yr-1以及1.14±0.52 Gt C yr-1,这与全球碳计划(GCP)得出的结果大致相符。海洋和陆地对于碳的吸收在2000年后有着加强的迹象,这反映了碳循环对人类活动不断增强的响应。此外,我们还将该结果与以CMIP5为基础得到的结果进行了对比,二者之间的差异反映出了氧数据集对碳沉降估计的重要影响。
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Acknowledgements
The authors acknowledge the Scripps O2 Program for providing the observations of atmospheric O2 and CO2 data. The authors also acknowledge the World Climate Recruitment Programme’s (WCRP) Working Group on Coupled Modelling (WGCM), and the Global Organization for Earth System Science Portals (GO-ESSP) for producing outputs of CMIP6 model simulations. This work was jointly supported by the National Science Foundation of China (Grant Nos. 41991231, 91937302) and the China 111 project (Grant No. B13045). The data processes and analysis are supported by Supercomputing Center of Lanzhou University.
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Article Highlights
• CMIP6 outputs are used to systematically analyze the characteristics of air-sea O2 flux under climate change.
• The study provides a valuable complement for global carbon sinks based on the tight relationship between oxygen and carbon cycle.
• The vital role of oceanic oxygen outgassing in O2-based estimations of land and ocean carbon uptake is revealed in this study.
This paper is a contribution to the special issue on Carbon Neutrality: Important Roles of Renewable Energies, Carbon Sinks, NETs and non-CO2 GHGs
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Li, C., Huang, J., Ding, L. et al. The Variability of Air-sea O2 Flux in CMIP6: Implications for Estimating Terrestrial and Oceanic Carbon Sinks. Adv. Atmos. Sci. 39, 1271–1284 (2022). https://doi.org/10.1007/s00376-021-1273-x
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DOI: https://doi.org/10.1007/s00376-021-1273-x