岡 顕 (Oka Akira)

東京大学大気海洋研究所 准教授

気候システム研究系
気候モデリング研究部門
海洋システムモデリング研究分野

<連絡先>

郵便：〒277-8568 千葉県柏市柏の葉5-1-5 総合研究棟 東京大学大気海洋研究所
居屋：東京大学柏キャンパス 総合研究棟2階211a室

研究テーマ
略歴
論文
講義

大気海洋研究所気候システム系 トップページへもどる

研究テーマ

研究の概要

地球の気候はさまざまな時間・空間スケールで変動しますが、数十年以上の長期気候変動においては海洋が重要な働きをします。なかでも海洋の深層まで含めた循環（海洋深層循環）は、1000年以上の時間スケールで全球的な気候に影響しています。
氷床コアデータによると、氷期において最大10度程度の温暖化イベントが数千年程度の周期で何度も起こっていることが見出されており、それは海洋深層循環の変動によるものではないかと考えられいます。また、氷期から現在にかけて気候が温暖化するなかで起きた大規模な寒冷化イベントも、海洋深層循環の停止によるものであると言われています。地球温暖化現象の進行とともに、現在の海洋深層循環が変化し、大きな気候変動を引き起こすという懸念もあります。
私は、過去に起こったあるいはこれから引き起こされうる長期気候変動について興味をもって研究を行っています。なかでも、海洋深層循環を気候モデル・海洋モデルによって再現するとともに、その安定性や変動のメカニズムの解明を目指しています。最近は、海洋深層に存在する炭素などの溶存物質の分布と海洋深層循環との関係についても興味を持っています。大気中二酸化炭素濃度を決めるプロセスとして、あるいは過去の循環の変動を記録する指標として、それらの物質循環についての理解がますます重要視されてきています。

研究トピック


略歴


学歴


職歴


所属学会


論文

査読論文（投稿中）
  1. Sugino, K. and A. Oka (2024) : Role of ocean circulation in controlling Zn-Si decoupling in the North Pacific, Global Biogeochemical Cycles, submitted.

査読論文
  1. Kobayashi, H., A. Oka, T. Obase, and A. Abe-Ouchi (2024): Assessing transient changes in the ocean carbon cycle during the last deglaciation through carbon isotope modeling, Climate of the Past, 20(3), 769-787.

  2. Yoshikawa, C., M. Shigemitsu, A. Yamamoto, A. Oka, and N. Ohkouchi (2024): A nitrogen isoscape of phytoplankton in the western North Pacific created with a marine nitrogen isotope model, Frontiers in Marine Science, 11, 1294608.

  3. Sherriff-Tadano, S., Abe-Ouchi, A., Yoshimori, M., Ohgaito, R., Vadsaria, T., Chan, W.L., Hotta, H., Kikuchi, M., Kodama, T., Oka, A. and Suzuki, K. (2023) : Southern Ocean surface temperatures and cloud biases in climate models connected to the representation of glacial deep ocean circulation. Journal of Climate, pp.1-38.

  4. Sugino, K. and A. Oka (2023) : Zinc and silicon biogeochemical decoupling in the North Pacific Ocean, Journal of Oceanography, 79(1), 61-76.

  5. Masuda, Y., Yamanaka, Y., Smith, S.L., Hirata, T., Nakano, H., Oka, A., Sumata, H. and Aita, M.N. (2023) : Acclimation by diverse phytoplankton species determines oceanic carbon to nitrogen ratios, Limnol. Oceanogr. Lett. https://doi.org/10.1002/lol2.10304

  6. Sasaki, Y., Kobayashi, H., & Oka, A. (2022): Global simulation of dissolved 231Pa and 230Th in the ocean and the sedimentary 231Pa230Th ratios with the ocean general circulation model COCO ver4.0. Geoscientific Model Development, 15(5), 2013-2033.

  7. Ando, T. and A. Oka (2021): Hysteresis of the glacial Atlantic Meridional Overturning Circulation controlled by thermal feedbacks, Geophysical Research Letters, 48(24), e2021GL095809.

  8. Sam Sherriff-Tadano, Ayako Abe-Ouchi, Akira Oka, Takahito Mitsui, and Fuyuki Saito (2021) : Does a difference in ice sheets between Marine Isotope Stages 3 and 5a affect the duration of stadials?: Implications from hosing experiments, Climate of the Past, 17(5), 1919-1936.

  9. F. Lhardy, N. Bouttes, D. M. Roche, A. Abe-Ouchi, Z. Chase, K. A. Crichton, R. Ivanovic, M. Jochum, M. Kageyama, H. Kobayashi, L. Menviel, J. Muglia, R. Nuterman, A. Oka, G. Vettoretti, A. Yamamoto (2021): A firrst intercomparison of the simulated LGM carbon results within PMIP-carbon: role of the ocean boundary conditions, Paleoceanography and Paleoclimatology, 36(10), e2021PA004302.

  10. Kobayashi, H., A. Oka, A. Yamamoto, and A. Abe-Ouchi (2021) : Glacial carbon cycle changes by Southern Ocean processes with sedimentary amplification, Science Advances, 7(35), eabg7723.

  11. Oka, A., A. Abe-Ouchi, S. Sherriff-Tadano, Y. Yokoyama, K. Kawamura,and H. Hasumi (2021) : Glacial mode shift of the Atlantic meridional overturning circulation by warming over the Southern Ocean. Commun Earth Environ 2, 169, https://doi.org/10.1038/s43247-021-00226-3.

  12. Masuda, Y., Y. Yamanaka, S. L. Smith, T. Hirata, H. Nakano, A. Oka, H. Sumata (2021) : Photoacclimation by phytoplankton determines the distribution of global subsurface chlorophyll maxima in the ocean. Commun Earth Environ 2, 128, https://doi.org/10.1038/s43247-021-00201-y.

  13. A. Oka, H. Tazoe, and H. Obata (2021) : Simulation of global distribution of rare earth elements in the ocean using an ocean general circulation model, Journal of Oceanography, 1-18.

  14. S. Sherriff-Tadano, A. Abe-Ouchi, and A. Oka (2021) : Impact of mid-glacial ice sheets on deep ocean circulation and global climate, Climate of the Past 17 (1), 95-110.

  15. A. Oka (2020) : Ocean carbon pump decomposition and its application to CMIP5 earth system model simulations, Progress in Earth and Planetary Science 7 (1), 1-17.

  16. AH MacDougall et al. [A.Oka listed in 21th author] (2020) : Is there warming in the pipeline? A multi-model analysis of the Zero Emissions Commitment from CO2, Biogeosciences 17 (11), 2987-3016.

  17. Y. Nakamura and A. Oka (2019) : CMIP5 model analysis of future changes in ocean net primary production focusing on differences among individual oceans and models, Journal of Oceanography, Journal of Oceanography 75 (5), 441-462.

  18. A. Yamamoto, A. Abe-Ouchi, R. Ohgaito, A. Ito, and A. Oka (2019) : Glacial CO2 decrease and deep-water deoxygenation by iron fertilization from glaciogenic dust, Climate of the Past 15 (3), 981-996.

  19. H. Kobayashi and A. Oka (2018) : The response of atmospheric pCO2 to the glacial changes in the Southern Ocean amplified by the carbonate compensation process, Paleoceanography and Paleoclimatology 33 (11), 1206-1229.

  20. M. Yoshimori, A. Abe-Ouchi, H. Tatebe, T. Nozawa, and A. Oka (2018) : The importance of ocean dynamical feedback for understanding the impact of mid-high latitude warming on tropical precipitation change, Journal of Climate, Journal of Climate 31 (6), 2417-2434.

  21. S. Sherriff-Tadano, A. Abe-Ouchi, M. Yoshimori, A. Oka, and W. Chan (2018) : Influence of glacial ice sheets on the Atlantic meridional overturning circulation through surface wind change under glacial climate, Climate dynamics 50 (7-8), 2881-2903.

  22. M. Shigemitsu, A. Yamamoto, A. Oka, and Y. Yamanaka (2017) : Uncertainty in CMIP5 future projetions of the ocean volume coccupied by low-oxygenated waters in the Eastern Tropical Pacific , Global Biogeochemical Cycles, doi:10.1002/2016GB005447.

  23. A. Oka and M. Watanabe (2017) : The post-2002 global surface warming slowdown caused by the subtropical Southern Ocean heating acceleration, Geophysical Research Letters, 44, doi:10.1002/2016GL072184.

  24. Dome Fuji Ice Core Project Members [A.Oka listed in 37th author] (2017): State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling. Science advances 3, e1600446.

  25. M. Yoshimori, M. Watanabe, H. Shiogama, A. Oka, A. Abe-Ouchi, R. Ohgaito, and Y. Kamae (2016) : A review of progress towards understanding the transient global-mean surface temperature response to radiative perturbation, Progress in Earth and Planetary Science 3 (1), 21

  26. M. Shigemitsu, N. Gruber, A. Oka, and Y. Yamanaka (2016) : Potential use of the N2/Ar ratio as a constraint on the oceanic fixed nitrogen loss, Global Biogeochemical Cycles, 30(4), 576-594.

  27. Yamamoto, A., A. Abe-Ouchi, M. Shigemitsu, A. Oka, K. Takahashi, R. Ohgaito, Y. Yamanaka (2015): Global deep ocean oxygenation by enhanced ventilation in the Southern Ocean under long-term global warming, Global Biogeochemical Cycles, 29(10), 1801-1815.

  28. Kobayashi, H., A. Abe-Ouchi, and A. Oka (2015): Role of Southern Ocean stratification in glacial atmospheric CO2 reduction evaluated by a three-dimensional ocean general circulation model, Paleoceanography, 30, doi:10.1002/2015PA002786.

  29. Kusahara, K., T. Sato, A. Oka, T. Obase, R. Greve, A. Abe-Ouchi, and H. Hasumi (2015): Modelling Antarctic marine cryosphere at the Last Glacial Maximum, Annals of Glaciology, 56(69), 425.

  30. Liu , G., K. Kojima, K. Yoshimura, and A. Oka (2014): Proxy interpretation of coral-recorded seawater δ18O using 1D model forced by isotope-incorporated GCM in tropical oceanic regions, Journal of Geophysical Research: Atmospheres, 119(21), 12021-12033.

  31. Yoshimori, M., A. Abe-Ouchi, M. Watanabe, A. Oka, and T. Ogura (2014): Robust seasonality of Arctic warming processes in two different versions of MIROC GCM, Journal of Climate , 27(16), 6358-6375.

  32. Yamamoto, A., Y. Yamanaka , A. Oka, and A. Abe-Ouchi (2014): Ocean oxygen depletion due to decomposition of submarine methane hydrate, Geophysical Research Letter , 41(14), 5075-5083.

  33. Ba, J., N. Keenlyside, M. Latif, W. Park, H. Ding, K. Lohmann, J. Mignot, M. Menary, O. H. Ottera, B. Wouters, D. Salas-Melia, A. Oka, A. Bellucci, E. Volodin (2014): A multi-model comparison for Atlantic multidecadal variability, Climate Dynamics, 43(9-10), 2333-2348.

  34. Oka, A. and Y. Niwa (2013): Pacific deep circulation and ventilation controlled by tidal mixing away from the sea bottom, Nature Communications, 4:2419, doi:10.1038/ncomms3419.

  35. Watanabe, M., Y. Kamae, M. Yoshimori, A. Oka, M. Sato, M. Ishii, T. Mochizuki, and M. Kimoto (2013): Strengthening of ocean heat uptake efficiency associated with the recent climate hiatus. Geophysical Research Letters, 40, 3175-3179, doi:10.1002/grl.50541.

  36. Chikamoto, O. M., A. Abe-Ouchi, A.Oka, and S. Lan Smith (2012): Temperature-induced marine export production during glacial period, Geophysical Research Letters, 39, doi:10.1029/2012GL053828.

  37. Oka, A., H. Hasumi, and A. Abe-Ouchi (2012): The thermal threshold of the Atlantic meridional overturning circulation and its control by wind stress forcing during glacial climate, Geophysical Research Letters, 39, doi:10.1029/2012GL051421.

  38. Chikamoto, O. M., A. Abe-Ouchi, A. Oka, R. Ohgaito (2012): Quantifying the ocean's role in glacial CO2 reductions, Climate of the Past, doi:10.5194/cp-8-545-2012.

  39. Chikamoto, O. M., L. Menviel, A. Abe-Ouchi, R. Ohgaito, A. Timmermann, Y. Okazaki, N. Harada, A. Oka (2012): Variability in North Pacific intermediate and deep water ventilation during Heinrich events in two coupled climate models, Deep Sea Research II, 61-64, 114-126.

  40. Oka, A., E. Tajika, A. Abe-Ouchi, and K. Kubota (2011): Role of ocean in controlling atmospheric CO2 concentration in the course of global glaciations, Climate Dynamics, 37, 1755-1770.

  41. Oka, A., A. Abe-Ouchi., M. Chikamoto, and T. Ide (2011): Mechanisms controlling export production at the LGM: effects of changes in oceanic physical fields and atmospheric dust deposition, Global Biogeochemical Cycles, 25, GB2009, doi:10.1029/2009GB003628.

  42. Tachiiri, K., J. C. Hargreaves, J. D. Annan, A. Oka, A. Abe-Ouchi, and M. Kawamiya (2010): Development of a system emulating the global carbon cycle in Earth system models, Geoscience model developement, 3, 365-376.

  43. Oka, A., H. Hasumi, H. Obata, T. Gamo, and Y. Yamanaka (2009): Study on vertical profiles of rare earth elements by using an ocean general circulation model, Global Biogeochemical Cycles, 23, GB4025, doi:10.1029/2008GB003353.

  44. Oka, A., S. Kato, and H. Hasumi (2008): Evaluating effect of ballast mineral on deep-ocean nutrient concentration by using an ocean general circulation model, Global Biogeochemical Cycles, 22, doi:10.1029/2007GB003067.

  45. R. J. Stouffer, J. Yin, J. M. Gregory, K. W. Dixon, M. J. Spelman, W. Hurlin, A. J. Weaver, M. Eby, G. M. Flato, H. Hasumi, A. Hu, J. Jungclause, I. V. Kamenkovich, A. Levermann, M. Montoya, S.Murakami, S. Nawrath, A. Oka, W. R. Peltier, D. Y. Robitaille, A. Sokolov, G. Vettoretti, N. Weber (2005): Investigating the causes of the response of the thermohaline circulation to past and future climate changes, Jornal of Climate, 19(8), 1365-1387.

  46. Oka, A., H. Hasumi, N. Okada, T. T. Sakamoto, and T. Suzuki (2006): Deep convection seesaw controlled by freshwater transport through the Denmark Strait. Ocean modelling, 15(3-4), 157-176.

  47. Oka, A., and H. Hasumi (2006): Effects of model resolution on salinity transport through northern high-latitude narrow passages and the Atlantic meridional overturning circulation, Ocean modelling, 13(2), 126-147.

  48. Suzuki, T., H. Hasumi, T. T. Sakamoto, T. Nishimura, A. Abe-Ouchi, T. Segawa, N. Okada, A. Oka and S. Emori (2005): Projection of future sea level and its variability in a high resolution climate model, Geophysical Research Letters, 32(19), Art.No.L19706.

  49. Suzuki, T., T.T.Sakamoto, T.Nishimura, N.Okada, S.Emori, A.Oka, and H.Hasumi (2005): Seasonal cycle of the Mindanao dome in the CCSR/NIES/FRCGC atmosphere ocean coupled model, Geophysical Research Letters, 32(17), Art.No.L19604.

  50. J. M. Gregory, K. W. Dixon, R. J. Stouffer, A. J. Weaver, E. Driesschaert, M. Eby, T.Fichefet, H. Hasumi, A. Hu, J. H. Jungclaus, I. V. Kamenkovich, A. Levermann, M. Montoya, S. Murakami, S. Nawrath, A. Oka, A. P. Sokolov, R. B. Thorpe (2005): A model intercomparison of changes in the Atlantic thermohaline circulation in response to increasing atmospheric CO2 concentration, Geophysical Research Letters, 32(12), Art.No.L12703.

  51. Oka, A., and H. Hasumi (2004): Effects of freshwater forcing on the Atlantic deep circulation: a study with an OGCM forced by two different surface freshwater flux datasets, Journal of Climate, 17(11), 2180-2194.

  52. Oka, A., H. Hasumi and N. Suginohara (2001): Stabilization of thermohaline circulation by wind-driven and vertical diffusive salt transport, Climate Dynamics, 18(1), 71-83.

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