open access

https://doi.org/10.14943/doctoral.k16085

https://hdl.handle.net/2115/93427

北太平洋における過去半世紀の海洋貧酸素化に対するCMIPモデルと観測との比較

英語

2024-09-25

Hokkaido University

63p

The amount of dissolved oxygen (O2) in the global ocean has been decreasing over the past half century. This phenomenon, called ocean deoxygenation, is one of the environmental problems associated with global warming that has attracted attention in recent years. It is important for the certainty of future predictions that the models adequately reproduce past O2 decreases. In Coupled Model Intercomparison Project (CMIP) Phase 5, the models underestimated the observations, which was problematic. In CMIP6, the model's O2 decrease falls within the variability of observations, but the comparison remains rough. Here we report the relationship between the observed and simulated O2 inventory changes in the North Pacific by analyzing observational data and the outputs of CMIP5 and 6 between 1958 and 2005 to understand the extent to which the CMIP models reproduce the observed O2 decrease. A total of 204 ensembles from 20 models were analyzed. Many of the models overestimate O2 climate values while some models show O2 decreases equal to or greater than observations. An inter-model empirical orthogonal function (EOF) analysis revealed that the different simulated magnitudes of the negative O2 trend is closely associated with the first EOF mode, and ensemble members with strong negative trends are characterized by large oxygen reduction in the subarctic North Pacific, especially around the boundaries between the North Pacific and the Sea of Okhotsk as well as the Bering Sea. The modeled strong O2 decrease in the subarctic North Pacific is consistent with the spatial pattern of the observed O2 trend. Further analysis of climate models indicated that the O2 decrease in the subarctic region was primarily caused by physical factors. This conclusion is supported by the significantly high correlation between the potential temperature and O2 inventory trend in the subarctic region, whereas an insignificant correlation coefficient is 2 present between dissolved organic carbon and the O2 inventory trend. However, the observations have a larger ratio of O2 inventory trend to temperature trend than any of the ensembles. Thus, the relationship between O2 and temperature change in the subarctic North Pacific seen in the CMIP5/6 simulations is not exact. Furthermore, we compared not only gridded data but also long-term observational data. At Station P, the models more significantly underestimated the trend and overestimated the climatological values compared to the observation. At 137°E, the observed O2 trend has decreased sharply in recent years, and the trend is outside the variability of the models. These detailed comparisons revealed that the CMIP models do not adequately reproduce the observed changes in O2 in the North Pacific.

2024-09-25

甲第16085号

博士(理学)

(主査) 教授 見延 庄士郎, 教授 稲津 將, 准教授 佐々木 克徳, 准教授 佐藤 陽祐, 纐纈 慎也（国立研究開発法人 海洋研究開発機構 海洋観測研究センター・センター長）

理学院（自然史科学専攻）

博士論文

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