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Sayaka Yasunaka

Section

Graduate School of Science

Job title

Professor

Degree

博士（理学）（東北大学）
修士（理学）（東北大学）

researchmap

https://researchmap.jp/yasunaka

J-GLOBAL ID

201501000545556290

Research History 12

2024/10 - Present

JAMSTEC　Senior Researcher (Cross Appointment)
2021/10 - Present

Tohoku University　Professor
2021/10 - 2024/03

JAMSTEC　Visiting Principal Researcher
2020/10 - 2021/09

JAMSTEC　Researcher
2020/01 - 2021/09

Tohoku University　Associate Professor (Cross Appointment)
2014/04 - 2020/09

JAMSTEC　Researcher
2011/07 - 2014/03

NIES　Research Associate
2009/04 - 2011/06

JSPS　Research Fellow (PD)
2007/04 - 2009/03

JSPS　Research Fellow (RPD)
2006/04 - 2006/07

Tohoku University　Research Assistant
2005/04 - 2006/03

JSPS　Research Fellow (PD)
2003/04 - 2005/03

JSPS　Research Fellow (DC2)

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Education 3

Tohoku University

2001/04 - 2005/03
Tohoku University

1999/04 - 2001/03
Tohoku University　Faculty of Science

1995/04 - 1999/03

Committee Memberships 16

Japan Society of Ocean Policy　Director

2024/12 - Present
JpGU　Representative

2024/04 - Present
Oceanographic Society of Japan　Officer/Director

2023/04 - Present
CLIVAR　Pacific Regional Panel, Member

2023/01 - Present
JAXA　Science Advisory Committee for earth observation, Member

2022/06 - Present
Japanese National Commission for UNESCO　Member

2022/04 - Present
JpGU　Atmospheric and Hydrospheric Sciences, Board Member

2021/04 - Present
CLIVAR-Japan Committee　Member

2021/04 - Present
JCAR　Steering Committee

2019/10 - Present
Oceanographic Society of Japan　Council Member

2019/04 - Present
SOLAS-Japan Committee　Member

2018/04 - Present
Oceanographic Society of Japan　Selection committee member of the Environmental Science Prize

2023/04 - 2025/05
Japan Society of Ocean Policy　PR comittee member

2021/04 - 2025/03
JSPS　Advisor for gender equality

2021/04 - 2022/03
Oceanographic Society of Japan　Officer

2017/04 - 2021/03
IOCCP Review Panel　Member

2018/06 - 2020/03

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Research Interests 2

Ocean Science
Ocean carbon and nutrient cycles

Research Areas 2

Environmental science/Agricultural science / Environmental dynamics /
Natural sciences / Atmospheric and hydrospheric science /

Awards 3

Environmental Science Prize

2023　Oceanographic Society of Japan
Hidaka Outstanding-Publication Award

2020　Oceanographic Society of Japan
Kuroda Chika Prize

2003　Aoba Promotion

Papers 41

Arctic marine environments regulated by ocean transport and air‒sea‒land interaction: Findings from the ArCS II Ocean Research Program

Eiji Watanabe, Hiromichi Ueno, Tsubasa Kodaira, Akihiko Murata, Shigeto Nishino, Takahito Ikenoue, Masanobu Yamamoto, Daiki Nomura, Hiroto Abe, Yusuke Kawaguchi, Daisuke Hirano, Yuanxin Zhang, Sayaka Yasunaka

Polar Science　101205-101205　2025/04
Publisher: Elsevier BV
DOI： 10.1016/j.polar.2025.101205 　

ISSN： 1873-9652
Spatiotemporal variation of high-temperature events and its relation to coral bleaching in the Ryukyu Islands, Japan

Sayaka Yasunaka, Haruko Kurihara, Takeshi Doi

Progress in Earth and Planetary Science　12　(1)　2025/01/21
Publisher: Springer Science and Business Media LLC
DOI： 10.1186/s40645-024-00673-4 　

eISSN： 2197-4284

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Abstract Coral bleaching occurs when symbiotic dinoflagellate algae leave corals due to warming surface waters. Since the early 1980s, the number and intensity of coral bleaching events have significantly risen globally, and many coral reefs are concerned to undergo irreversible phase shifts due to global warming. In this study, we examine spatiotemporal variations and relationships of high-temperature events, high-temperature anomaly events, and coral bleaching around the Ryukyu Islands, Japan. We also explore the correlation between these occurrences and the large-scale climate variability, El Niño–Southern Oscillation and Indian Ocean Dipole. More than 99% of the high-temperature events occurred from June to October, and more than 80% occurred from July to September, whereas high-temperature anomaly events occurred all year round. Corresponding with high-temperature events, more than 10% of the data reported overall bleaching, and more than 25% reported partial bleaching from June to October. Over 40% of data reported bleaching in August, of which 50% of these reports were categorized as overall bleaching and the remainder as partial. The spatial distribution of coral bleaching also corresponded better with high-temperature events than high-temperature anomaly events. In 2016, extensive and severe coral bleaching was reported around the Okinawa, Miyako, and Yaeyama Islands, where intense high-temperature events had occurred. The central-to-eastern equatorial Pacific displayed a negative sea surface temperature anomaly, and the eastern Indian Ocean did a positive anomaly following high-temperature events near the Ryukyu Islands. These findings indicated that the high-temperature events around the Ryukyu Islands show correlation with La Niña and a negative Indian Ocean Dipole. If the cumulative temperature of high-temperature events exceeds 56 °C-days every three years in the late 2030s, then the corals around the Ryukyu Islands will suffer high mortality within 20 years.
Quantitative Assessment of Factors Contributing to Variations in Sea Surface pCO₂ in the Pacific Sector of the Arctic Ocean

Manami Tozawa, Daiki Nomura, Mirai Matsuura, Mariko Hatta, Amane Fujiwara, Sayaka Yasunaka, Akihiko Murata

Journal of Geophysical Research: Oceans　129　(6)　2024/06/06
Publisher: American Geophysical Union (AGU)
DOI： 10.1029/2024jc021012 　

ISSN： 2169-9275

eISSN： 2169-9291

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Abstract To quantitatively assess seasonal variations in the partial pressure of carbon dioxide (pCO₂) in the Pacific sector of the Arctic Ocean (Canada Basin and Chukchi Sea) in 2021, water temperature, salinity, chlorophyll‐a, pCO₂, dissolved inorganic carbon (DIC), total alkalinity (TA), and nutrients were measured. During summer 2021, surface water pCO₂ in our study area (315 ± 41 μatm) was undersaturated with respect to the atmosphere (404 ± 4 μatm), and the ocean was a sink for atmospheric CO₂ (−10.5 ± 11.0 mmol C m⁻² day⁻¹). Using DIC, TA, and nutrients in the temperature minimum layer, we estimated the under‐ice pCO₂ in the water during the previous winter and calculated changes in pCO₂ (δpCO₂) due to temperature changes, freshwater inflow, biological activity, and other factors (gas exchange and advection) from winter to summer. In the Chukchi Sea, biological activity and temperature changes had significant impacts on pCO₂, whereas in the Canada Basin, the influx of freshwater caused a significant decrease in pCO₂. Our results suggested that different types of freshwaters had different effects on pCO₂, with sea ice meltwater having a greater effect on reducing pCO₂ than river water or snowmelt water. We therefore emphasize the importance of freshwater type and proportion, as well as freshwater supply, for prediction of future pCO₂ changes.
An Assessment of CO₂ Uptake in the Arctic Ocean From 1985 to 2018 Peer-reviewed

Sayaka Yasunaka, Manfredi Manizza, Jens Terhaar, Are Olsen, Ryohei Yamaguchi, Peter Landschützer, Eiji Watanabe, Dustin Carroll, Hanani Adiwira, Jens Daniel Müller, Judith Hauck

Global Biogeochemical Cycles　37　(11)　2023/11/10
Publisher: American Geophysical Union (AGU)
DOI： 10.1029/2023gb007806 　

ISSN： 0886-6236

eISSN： 1944-9224

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Abstract As a contribution to the Regional Carbon Cycle Assessment and Processes phase 2 (RECCAP2) project, we present synthesized estimates of Arctic Ocean sea‐air CO₂ fluxes and their uncertainties from surface ocean pCO₂‐observation products, ocean biogeochemical hindcast and data assimilation models, and atmospheric inversions. For the period of 1985–2018, the Arctic Ocean was a net sink of CO₂ of 116 ± 4 TgC yr⁻¹ in the pCO₂ products, 92 ± 30 TgC yr⁻¹ in the models, and 91 ± 21 TgC yr⁻¹ in the atmospheric inversions. The CO₂ uptake peaks in late summer and early autumn, and is low in winter when sea ice inhibits sea‐air fluxes. The long‐term mean CO₂ uptake in the Arctic Ocean is primarily caused by steady‐state fluxes of natural carbon (70% ± 15%), and enhanced by the atmospheric CO₂ increase (19% ± 5%) and climate change (11% ± 18%). The annual mean CO₂ uptake increased from 1985 to 2018 at a rate of 31 ± 13 TgC yr⁻¹ dec⁻¹ in the pCO₂ products, 10 ± 4 TgC yr⁻¹ dec⁻¹ in the models, and 32 ± 16 TgC yr⁻¹ dec⁻¹ in the atmospheric inversions. Moreover, 77% ± 38% of the trend in the net CO₂ uptake over time is caused by climate change, primarily due to rapid sea ice loss in recent years. Furthermore, true uncertainties may be larger than the given ensemble standard deviations due to common structural biases across all individual estimates.
Magnitude, Trends, and Variability of the Global Ocean Carbon Sink From 1985 to 2018 Peer-reviewed

Tim DeVries, Kana Yamamoto, Rik Wanninkhof, Nicolas Gruber, Judith Hauck, Jens Daniel Müller, Laurent Bopp, Dustin Carroll, Brendan Carter, Thi‐Tuyet‐Trang Chau, Scott C. Doney, Marion Gehlen, Lucas Gloege, Luke Gregor, Stephanie Henson, Ji Hyun Kim, Yosuke Iida, Tatiana Ilyina, Peter Landschützer, Corinne Le Quéré, David Munro, Cara Nissen, Lavinia Patara, Fiz F. Pérez, Laure Resplandy, Keith B. Rodgers, Jörg Schwinger, Roland Séférian, Valentina Sicardi, Jens Terhaar, Joaquin Triñanes, Hiroyuki Tsujino, Andrew Watson, Sayaka Yasunaka, Jiye Zeng

Global Biogeochemical Cycles　37　(10)　2023/10/17
Publisher: American Geophysical Union (AGU)
DOI： 10.1029/2023gb007780 　

ISSN： 0886-6236

eISSN： 1944-9224

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Abstract This contribution to the RECCAP2 (REgional Carbon Cycle Assessment and Processes) assessment analyzes the processes that determine the global ocean carbon sink, and its trends and variability over the period 1985–2018, using a combination of models and observation‐based products. The mean sea‐air CO₂ flux from 1985 to 2018 is −1.6 ± 0.2 PgC yr⁻¹ based on an ensemble of reconstructions of the history of sea surface pCO₂ (pCO₂ products). Models indicate that the dominant component of this flux is the net oceanic uptake of anthropogenic CO₂, which is estimated at −2.1 ± 0.3 PgC yr⁻¹ by an ensemble of ocean biogeochemical models, and −2.4 ± 0.1 PgC yr⁻¹ by two ocean circulation inverse models. The ocean also degasses about 0.65 ± 0.3 PgC yr⁻¹ of terrestrially derived CO₂, but this process is not fully resolved by any of the models used here. From 2001 to 2018, the pCO₂ products reconstruct a trend in the ocean carbon sink of −0.61 ± 0.12 PgC yr⁻¹ decade⁻¹, while biogeochemical models and inverse models diagnose an anthropogenic CO₂‐driven trend of −0.34 ± 0.06 and −0.41 ± 0.03 PgC yr⁻¹ decade⁻¹, respectively. This implies a climate‐forced acceleration of the ocean carbon sink in recent decades, but there are still large uncertainties on the magnitude and cause of this trend. The interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate‐driven variability exceeding the CO₂‐forced variability by 2–3 times. These results suggest that anthropogenic CO₂ dominates the ocean CO₂ sink, while climate‐driven variability is potentially large but highly uncertain and not consistently captured across different methods.
Anomalous Nutricline Drives Marked Biogeochemical Contrasts During the Kuroshio Large Meander Peer-reviewed

Hakase Hayashida, Andrew E. Kiss, Toru Miyama, Yasumasa Miyazawa, Sayaka Yasunaka

Journal of Geophysical Research: Oceans　128　(7)　2023/07/11
Publisher: American Geophysical Union (AGU)
DOI： 10.1029/2023jc019697 　

ISSN： 2169-9275

eISSN： 2169-9291

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Abstract The large meander (LM) of the Kuroshio western boundary current is well known to influence the local climate, fisheries, and aquaculture by greatly modulating regional heat transport, but its impact on biogeochemical processes remains unclear. Using a high‐resolution numerical ocean model and long‐term observational datasets, we show that the path of the Kuroshio south of Japan determines the extent of the shallow nutricline region, where winter convective mixing replenishes nutrient availability for subsequent blooms of phytoplankton during spring. During the LM phase, this mechanism triggers offshore phytoplankton blooms that can be twice as strong as those during the non‐large meander phase. In contrast, spring blooms are weaker in the nearshore region where the nutricline depth is deeper, which reduces the nutrient supply by winter convective mixing during the LM. The LM also modulates the spatial distributions of primary production, air‐sea carbon flux, and export production. Hence, the Kuroshio path variability has broader implications for marine ecosystems and biogeochemical cycles. The biogeochemical impacts of the Kuroshio LM exert bottom‐up control on regional marine ecosystems that may be disproportionate to its thermal effect, and therefore need to be assessed to understand the LM's overall impacts on fisheries and aquaculture.
Simulated decadal variations of surface and subsurface phytoplankton in the upstream Kuroshio Extension region Peer-reviewed

Tomoki Tozuka, Yoshikazu Sasai, Sayaka Yasunaka, Hideharu Sasaki, Masami Nonaka

PROGRESS IN EARTH AND PLANETARY SCIENCE　9　(1)　2022/12

DOI： 10.1186/s40645-022-00532-0 　

ISSN： 2197-4284
Early Wintertime CO ₂ Uptake in the Western Arctic Ocean Peer-reviewed

A. Murata, J. Inoue, S. Nishino, S. Yasunaka

Journal of Geophysical Research: Oceans　127　(8)　2022/08
Publisher: American Geophysical Union (AGU)
DOI： 10.1029/2021jc018037 　

ISSN： 2169-9275

eISSN： 2169-9291
Overview: Recent advances in the understanding of the northern Eurasian environments and of the urban air quality in China – a Pan-Eurasian Experiment (PEEX) programme perspective Peer-reviewed

Lappalainen, H. K, Petäjä, T, Vihma, T, Räisänen, J, Baklanov, A, Chalov, S, Esau, I, Ezhova, E, Leppäranta, M, Pozdnyakov, D, Pumpanen, J, Andreae, M. O, Arshinov, M, Asmi, E, Bai, J, Bashmachnikov, I, Belan, B, Bianchi, F, Biskaborn, B, Boy, M, Bäck, J, Cheng, B, Chubarova, N, Duplissy, J, Dyukarev, E, Eleftheriadis, K, Forsius, M, Heimann, M, Juhola, S, Konovalov, V, Konovalov, I, Konstantinov, P, Köster, K, Lapshina, E, Lintunen, A, Mahura, A, Makkonen, R, Malkhazova, S, Mammarella, I, Mammola, S, Buenrostro Mazon, S, Meinander, O, Mikhailov, E, Miles, V, Myslenkov, S, Orlov, D, Paris, J.-D, Pirazzini, R, Popovicheva, O, Pulliainen, J, Rautiainen, K, Sachs, T, Shevchenko, V, Skorokhod, A, Stohl, A, Suhonen, E, Thomson, E. S, Tsidilina, M, Tynkkynen, V.-P, Uotila, P, Virkkula, A, Voropay, N, Wolf, T, Yasunaka, S, Zhang, J, Qiu, Y, Ding, A, Guo, H, Bondur, V, Kasimov, N, Zilitinkevich, S, Kerminen, V.-M, Kulmala, M

Atmos. Chem. Phys.　22　4413-4469　2022

DOI： 10.5194/acp-22-4413-2022 　
Global distribution and variability of subsurface chlorophyll &lt;i&gt;a&lt;/i&gt; concentrations Peer-reviewed

Sayaka Yasunaka, Tsuneo Ono, Kosei Sasaoka, Kanako Sato

Ocean Science　18　(1)　255-268　2022
Publisher: Copernicus GmbH
DOI： 10.5194/os-18-255-2022 　

eISSN： 1812-0792

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Abstract. Chlorophyll a (Chl a) often exhibits a maximumconcentration in the subsurface layer rather that at the surface. The depthof the Chl a maximum primarily depends on the balance between lightpenetration from the surface and the nutrient supply from the deep ocean.However, a global map of subsurface Chl a concentrations based onobservations has not been presented yet. In this study, we integrate Chl aconcentration data from recent biogeochemical floats andhistorical ship-based (and other) observations and present global maps ofsubsurface Chl a concentrations with related variables. The subsurface Chl amaximum was observed globally throughout the oceans: at depths greater than80 m in the subtropics and tropics (30∘ S to 30∘ N); inthe 40–80 m depth range in the tropics, in the Southern Ocean (south of40∘ S), and at the midlatitudes (30–40∘ N/S) in theNorth Pacific; and at depths of less than 40 m in the northern subarctic(north of 40∘ N). The observed maxima all lie below the mixed-layer depth for the entire year in the subtropics and tropics and duringsummer in the midlatitudes and the northern subarctic. The depths of thesubsurface Chl a maxima are greater than those of the photosyntheticallyactive layer in the subtropics but shallower in the tropics andmidlatitudes. In the subtropics, a seasonal increase in oxygen below themixed layer implies substantial new biological production, which correspondsto 10 % of the net primary production in that region. During El Niño,subsurface Chl a concentrations are higher in the middle and easternequatorial Pacific but lower to the west in comparison with La Niña, apattern which is opposite to that on the surface. The spatiotemporalvariability of the Chl a concentrations described here has implications tonot only for the biogeochemical cycling in the ocean but also forunderstanding the thermal structure and dynamics of the ocean via absorptionof shortwave radiation.
Decadal vision in oceanography 2021: Polar oceans Peer-reviewed

Michiyo Yamamoto-Kawai, Takeshi Tamura, Eiji Watanabe, Jun Nishioka, Daiki Nomura, Ryusuke Makabe, Kohei Mizobata, Yasunaka Sayaka

Oceanography in Japan　30　(5)　159-178　2021/11
Publisher: The Oceanographic Society of Japan
DOI： 10.5928/kaiyou.30.5_159 　

ISSN： 0916-8362

eISSN： 2186-3105
Decadal vision in oceanography 2021: Tropical oceans Peer-reviewed

Doi Takeshi, Yasunaka Sayaka, Takahashi Kazutaka, Watanabe Michio, Tozuka Tomoki, Haruko Kurihara and

Oceanography in Japan　30　(5)　105-129　2021/11
Publisher: The Oceanographic Society of Japan
DOI： 10.5928/kaiyou.30.5_105 　

ISSN： 0916-8362

eISSN： 2186-3105

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A review of progress in oceanographic research in the tropics over the past decade is provided. Physical and biogeochemical oceanographic perspectives regarding directions for the next decade are proposed, with a special focus on the El Niño-Southern Oscillation (ENSO) in the tropical Pacific. Although physical understanding of the ENSO has considerably advanced and its dynamical prediction has now become possible, our understanding of mechanisms and ability to predict variations in the material cycles, biological production, and biodiversity associated with the ENSO is still rudimentary. Because effects of internal natural climate variability on the marine system (e.g., ocean warming, acidification, and deoxygenation) have become more serious with global warming, comprehensive understanding and more accurate prediction of the ENSO and its effects on the tropical ocean system are becoming increasingly important. This research will also be key to anticipating changing societal needs as ocean conditions change. In particular, basin-scale studies based on Biogeochemical Argo floats and earth system models, process-oriented studies based on ship/buoy observations and experiment/observation by local research stations, and feedback between the basin-scale studies and the process-oriented studies will be key in the coming decade. The tropical Pacific is an optimal testbed for innovative cross-disciplinary programs that contribute to better understanding and prediction of the ocean system, because its interannual variations associated with the ENSO are highly predictable relative to other oceans.
Nutrient and dissolved inorganic carbon variability in the North Pacific Peer-reviewed

Sayaka Yasunaka, Humio Mitsudera, Frank Whitney, Shin-ichiro Nakaoka

JOURNAL OF OCEANOGRAPHY　77　(1)　3-16　2020

DOI： 10.1007/s10872-020-00561-7 　

ISSN： 0916-8370

eISSN： 1573-868X
Addressing Arctic challenges requires a synoptic ocean survey Peer-reviewed

Øyvind Paasche, Are Olsen, Marius Årthun, Leif G. Anderson, Sten-Åke Wängberg, Carin J. Ashjian, Jacqueline M. Grebmeier, Takashi Kikuchi, Shigeto Nishino, Sayaka Yasunaka, Sung-Ho Kang, Kyoung-Ho Cho, Kumiko Azetsu-Scott, William J. Williams, Eddy Carmack, Sinhué Torres-Valdés, Toby Tyrrell, Karen Edelvang, Jianfeng He, and Heidi Marie Kassens

EOS　100　2019

DOI： 10.1029/2019EO136200 　
Spatio-temporal variability of surface water pCO2 and nutrients in the tropical Pacific from 1981 to 2015 Peer-reviewed

Yasunaka, S., S. Kouketsu, P.G. Strutton, A.J. Sutton, A. Murata, S. Nakaoka, Y. Nojiri

Deep Sea Res. Part II　167-170　104680　2019
Publisher: Deep Sea Res. Part II
DOI： 10.1016/j.dsr2.2019.104680 　
Deployment of drifting buoys with pCO 2 sensors in the Pacific Ocean

Akihiko Murata, Yoshiyuki Nakano, Shuhei Masuda, Sayaka Yasunaka, Kousei Sasaoka, Masahide Wakita

2018 OCEANS - MTS/IEEE Kobe Techno-Oceans, OCEANS - Kobe 2018　2018/12/04
Publisher: Institute of Electrical and Electronics Engineers Inc.
DOI： 10.1109/OCEANSKOBE.2018.8559125 　
Arctic Ocean CO2 uptake: An improved multiyear estimate of the air-sea CO2 flux incorporating chlorophyll a concentrations Peer-reviewed

Sayaka Yasunaka, Eko Siswanto, Are Olsen, Mario Hoppema, Eiji Watanabe, Agneta Fransson, Melissa Chierici, Akihiko Murata, Siv K. Lauvset, Rik Wanninkhof, Taro Takahashi, Naohiro Kosugi, Abdirahman M. Omar, Steven Van Heuven, Jeremy T. Mathis

Biogeosciences　15　(6)　1643-1661　2018/03/22
Publisher: Copernicus GmbH
DOI： 10.5194/bg-15-1643-2018 　

ISSN： 1726-4189 1726-4170
Basin-scale distribution of NH4 + and NO2 − in the Pacific Ocean Peer-reviewed

Sayaka Yasunaka, Yukihiro Nojiri, Taketo Hashioka, Chisato Yoshikawa, Taketoshi Kodama, Shin-ichiro Nakaoka, Sanae Chiba, Fuminori Hashihama, Masahide Wakita, Ken Furuya, Daisuke Sasano, Akihiko Murata, Hiroshi Uchida, Michio Aoyama

Journal of Oceanography　74　(1)　1-11　2018/02/01
Publisher: Springer Tokyo
DOI： 10.1007/s10872-017-0433-1 　

ISSN： 1573-868X 0916-8370
Biological organic carbon export estimated from the annual carbon budget observed in the surface waters of the western subarctic and subtropical North Pacific Ocean from 2004 to 2013 Peer-reviewed

Masahide Wakita, Makio C. Honda, Kazuhiko Matsumoto, Tetsuichi Fujiki, Hajime Kawakami, Sayaka Yasunaka, Yoshikazu Sasai, Chiho Sukigara, Mario Uchimiya, Minoru Kitamura, Toru Kobari, Yoshihisa Mino, Akira Nagano, Shuichi Watanabe, Toshiro Saino

JOURNAL OF OCEANOGRAPHY　72　(5)　665-685　2016/10

DOI： 10.1007/s10872-016-0379-8 　

ISSN： 0916-8370

eISSN： 1573-868X
Mapping of the air-sea CO2 flux in the Arctic Ocean and its adjacent seas: Basin-wide distribution and seasonal to interannual variability Peer-reviewed

Sayaka Yasunaka, Akihiko Murata, Eiji Watanabe, Melissa Chierici, Agneta Fransson, Steven van Heuven, Mario Hoppema, Masao Ishii, Truls Johannessen, Naohiro Kosugi, Siv K. Lauvset, Jeremy T. Mathis, Shigeto Nishino, Abdirahman M. Omar, Are Olsen, Daisuke Sasano, Taro Takahashi, Rik Wanninkhof

POLAR SCIENCE　10　(3)　323-334　2016/09

DOI： 10.1016/j.polar.2016.03.006 　

ISSN： 1873-9652

eISSN： 1876-4428
Long-term variability of surface nutrient concentrations in the North Pacific Peer-reviewed

S. Yasunaka, T. Ono, Y. Nojiri, F. A. Whitney, C. Wada, A. Murata, S. Nakaoka, S. Hosoda

GEOPHYSICAL RESEARCH LETTERS　43　(7)　3389-3397　2016/04

DOI： 10.1002/2016GL068097 　

ISSN： 0094-8276

eISSN： 1944-8007
Mapping of sea surface nutrients in the North Pacific: Basin-wide distribution and seasonal to interannual variability Peer-reviewed

Sayaka Yasunaka, Yukihiro Nojiri, Shin-ichiro Nakaoka, Tsuneo Ono, Frank A. Whitney, Maciej Telszewski

JOURNAL OF GEOPHYSICAL RESEARCH-OCEANS　119　(11)　7756-7771　2014/11

DOI： 10.1002/2014JC010318 　

ISSN： 2169-9275

eISSN： 2169-9291
North Pacific dissolved inorganic carbon variations related to the Pacific Decadal Oscillation Peer-reviewed

Sayaka Yasunaka, Yukihiro Nojiri, Shin-ichiro Nakaoka, Tsuneo Ono, Hitoshi Mukai, Norihisa Usui

GEOPHYSICAL RESEARCH LETTERS　41　(3)　1005-1011　2014/02

DOI： 10.1002/2013GL058987 　

ISSN： 0094-8276

eISSN： 1944-8007
Upper ocean warming pattern in the past 50 years Peer-reviewed

Sayaka Yasunaka, Masahide Kimoto

Journal of Oceanography　69　(1)　87-95　2013

DOI： 10.1007/s10872-012-0159-z 　

ISSN： 0916-8370
An overview of decadal climate predictability in a multi-model ensemble by climate model MIROC Peer-reviewed

Yoshimitsu Chikamoto, Masahide Kimoto, Masayoshi Ishii, Takashi Mochizuki, Takashi T. Sakamoto, Hiroaki Tatebe, Yoshiki Komuro, Masahiro Watanabe, Toru Nozawa, Hideo Shiogama, Masato Mori, Sayaka Yasunaka, Yukiko Imada

Climate Dynamics　40　(5-6)　1201-1222　2013

DOI： 10.1007/s00382-012-1351-y 　

ISSN： 0930-7575 1432-0894

eISSN： 1432-0894
Estimating temporal and spatial variation of ocean surface pCO(2) in the North Pacific using a self-organizing map neural network technique Peer-reviewed

S. Nakaoka, M. Telszewski, Y. Nojiri, S. Yasunaka, C. Miyazaki, H. Mukai, N. Usui

BIOGEOSCIENCES　10　(9)　6093-6106　2013

DOI： 10.5194/bg-10-6093-2013 　

ISSN： 1726-4170

eISSN： 1726-4189
Monthly maps of sea surface dissolved inorganic carbon in the North Pacific: Basin-wide distribution and seasonal variation Peer-reviewed

Sayaka Yasunaka, Yukihiro Nojiri, Shin-Ichiro Nakaoka, Tsuneo Ono, Hitoshi Mukai, Norihisa Usui

Journal of Geophysical Research: Oceans　118　(8)　3843-3850　2013
Publisher: Blackwell Publishing Ltd
DOI： 10.1002/jgrc.20279 　

ISSN： 2169-9291
The Initialization of the MIROC Climate Models with Hydrographic Data Assimilation for Decadal Prediction Peer-reviewed

Hiroaki Tatebe, Masayoshi Ishii, Takashi Mochizuki, Yoshimitsu Chikamoto, Takashi T. Sakamoto, Yoshiki Komuro, Masato Mori, Sayaka Yasunaka, Masahiro Watanabe, Koji Ogochi, Tatsuo Suzuki, Teruyuki Nishimura, Masahide Kimoto

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN　90A　275-294　2012/02

DOI： 10.2151/jmsj.2012-A14 　

ISSN： 0026-1165

eISSN： 2186-9057
Predictability of a Stepwise Shift in Pacific Climate during the Late 1990s in Hindcast Experiments Using MIROC Peer-reviewed

Yoshimitsu Chikamoto, Masahide Kimoto, Masayoshi Ishii, Masahiro Watanabe, Toru Nozawa, Takashi Mochizuki, Hiroaki Tatebe, Takashi T. Sakamoto, Yoshiki Komuro, Hideo Shiogama, Masato Mori, Sayaka Yasunaka, Yukiko Imada, Hiroshi Koyama, Masato Nozu, Fei-fei Jin

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN　90A　1-21　2012/02

DOI： 10.2151/jmsj.2012-A01 　

ISSN： 0026-1165

eISSN： 2186-9057
Influence of XBT Temperature Bias on Decadal Climate Prediction with a Coupled Climate Model Peer-reviewed

Sayaka Yasunaka, Masayosh Ishii, Masahide Kimoto, Takashi Mochizuki, Hideo Shiogama

JOURNAL OF CLIMATE　24　(20)　5303-5308　2011/10

DOI： 10.1175/2011JCLI4230.1 　

ISSN： 0894-8755
Intercomparison of historical sea surface temperature datasets Peer-reviewed

Sayaka Yasunaka, Kimio Hanawa

INTERNATIONAL JOURNAL OF CLIMATOLOGY　31　(7)　1056-1073　2011/06

DOI： 10.1002/joc.2104 　

ISSN： 0899-8418

eISSN： 1097-0088
Impact of the Assimilation of Sea Ice Concentration Data on an Atmosphere-Ocean-Sea Ice Coupled Simulation of the Arctic Ocean Climate Peer-reviewed

Takahiro Toyoda, Toshiyuki Awaji, Nozomi Sugiura, Shuhei Masuda, Hiromichi Igarashi, Yuji Sasaki, Yoshihisa Hiyoshi, Yoichi Ishikawa, Takashi Mochizuki, Takashi T. Sakamoto, Hiroaki Tatebe, Yoshiki Komuro, Tatsuo Suzuki, Teruyuki Nishimura, Masato Mori, Yoshimitsu Chikamoto, Sayaka Yasunaka, Yukiko Imada, Miki Arai, Masahiro Watanabe, Hideo Shiogama, Toru Nozawa, Akira Hasegawa, Masayoshi Ishii, Masahide Kimoto

SOLA　7　37-40　2011

DOI： 10.2151/sola.2011-010 　

ISSN： 1349-6476
Pacific decadal oscillation hindcasts relevant to near-term climate prediction Peer-reviewed

Takashi Mochizuki, Masayoshi Ishii, Masahide Kimoto, Yoshimitsu Chikamoto, Masahiro Watanabe, Toru Nozawa, Takashi T. Sakamoto, Hideo Shiogama, Toshiyuki Awaji, Nozomi Sugiura, Takahiro Toyoda, Sayaka Yasunaka, Hiroaki Tatebe, Masato Mori

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA　107　(5)　1833-1837　2010/02

DOI： 10.1073/pnas.0906531107 　

ISSN： 0027-8424
Possible Influence of Volcanic Activity on the Decadal Potential Predictability of the Natural Variability in Near-Term Climate Predictions Peer-reviewed

Hideo Shiogama, Seita Emori, Takashi Mochizuki, Sayaka Yasunaka, Tokuta Yokohata, Masayoshi Ishii, Toru Nozawa, Masahide Kimoto

ADVANCES IN METEOROLOGY　2010　2010

DOI： 10.1155/2010/657318 　

ISSN： 1687-9309

eISSN： 1687-9317
日本の冬季気温の経年変動とその大規模大気循環場との関係 Peer-reviewed

安中さやか, 花輪公雄

天気　55　149-158　2008
Interannual summer temperature variations over Japan and their relation to large-scale atmospheric circulation field Peer-reviewed

Sayaka Yasunaka, Kimio Hanawa

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN　84　(4)　641-652　2006/08

DOI： 10.2151/jmsj.84.641 　

ISSN： 0026-1165
Regime shift in the global sea-surface temperatures: Its relation to El Nino-southern oscillation events and dominant variation modes Peer-reviewed

S Yasunaka, K Hanawa

INTERNATIONAL JOURNAL OF CLIMATOLOGY　25　(7)　913-930　2005/06

DOI： 10.1002/joc.1172 　

ISSN： 0899-8418

eISSN： 1097-0088
Regime shifts in the Northern Hemisphere SST field: Revisited in relation to tropical variations Peer-reviewed

S Yasunaka, K Hanawa

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN　81　(2)　415-424　2003/04

DOI： 10.2151/jmsj.81.415 　

ISSN： 0026-1165
Regime shifts found in the Northern Hemisphere SST field Peer-reviewed

S Yasunaka, K Hanawa

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN　80　(1)　119-135　2002/02

DOI： 10.2151/jmsj.80.119 　

ISSN： 0026-1165

eISSN： 2186-9057
Arctic Oscillation and corresponding sea surface temperature anomaly fields Peer-reviewed

Yasunaka, S, K. Hanawa

Tohoku Geophys. J.　36　47-63　2001
Examination of correction to historical SST data using long-term coastal SST data taken around Japan Peer-reviewed

K Hanawa, S Yasunaka, T Manabe, N Iwasaka

JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN　78　(2)　187-195　2000/04

DOI： 10.2151/jmsj1965.78.2_187 　

ISSN： 0026-1165

eISSN： 2186-9057

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Misc. 21

海洋表層生物地球化学パラメータの広域分布と季節経年変動

安中さやか

月刊海洋　640　275-280　2024/04
気候-生態系の構造転換: レジームシフト

安中さやか

岩波科学　93　(12)　1030-1032　2023/12
混合層の炭素収支から見積もられた西部北太平洋亜寒帯域・亜熱帯域における有機炭素の輸送フラックス

脇田昌英, 本多牧生, 松本和彦, 藤木徹一, 川上創, 安中さやか, 笹井義一, 鋤柄千穂, 内宮万里央, 喜多村稔, 小針統, 三野義尚, 永野憲, 渡邉修一, 才野敏郎

日本海洋学会大会講演要旨集　2016　2016
A164 海洋表層CO_2観測と広域分布推定研究の動向(温室効果気体研究の観測・測定技術の進展による新たな展開,スペシャル・セッション)

中岡慎一郎, 野尻幸宏, 安中さやか, 小埜恒夫, 向井人史

大会講演予講集　108　114-114　2015
Publisher: 日本気象学会
北極海CO2フラックスの分布推定とその時空間変動特性

安中さやか, 村田昌彦, 内田裕, 渡邉英嗣, 西野茂人, 小杉如央, 笹野大輔, 石井雅男

日本海洋学会大会講演要旨集　2014　2014
北極海CO2フラックスの分布推定とその時空間変動特性

安中さやか, 村田昌彦, 渡邉英嗣, 小杉如央, 笹野大輔, 石井雅男, 西野茂人, 内田裕

極域科学シンポジウム講演予稿集(CD-ROM)　5th　2014
気候・海洋の長期変動と近年の動向 : 気候レジームシフトの生起条件

安中さやか, 花輪公雄

水産海洋研究　76　(4)　212-213　2012/11/01

ISSN： 0916-1562
B102 大気海洋結合モデルMIROCに見られるPDO : 中緯度固有モード(気候システムI,一般口頭発表)

森正人, 木本昌秀, 渡部雅浩, 安中さやか, 今田由紀子, 建部洋晶, 石井正好

大会講演予講集　97　77-77　2010
Publisher: 日本気象学会
C157 アンサンブルデータ同化手法を用いた近未来気候変動予測実験(様々な時間スケールでのデータ同化とアンサンブル予測,専門分科会)

望月崇, 石井正好, 木本昌秀, 近本喜光, 渡部雅浩, 野沢徹, 坂本天, 塩竈秀夫, 淡路敏之, 杉浦望実, 豊田隆寛, 安中さやか, 建部洋晶, 森正人

大会講演予講集　97　136-136　2010
Publisher: 日本気象学会
P126 歴史的海面水温データセットの相互比較(ポスターセッション)

安中さやか, 花輪公雄

大会講演予講集　97　243-243　2010
Publisher: 日本気象学会
Regime shifts in global SSTs during the last centenary

Kaiyo monthly　40　(8)　439-447　2008/10
Publisher: 海洋出版
ISSN： 0916-2011
A357 大気海洋結合モデルを用いた1997/98年El Ninoイベントの予測(予測可能性,スペシャル・セッション「データ同化と予測可能性」II)

近本喜光, 木本昌秀, 渡部雅浩, 建部洋晶, 安中さやか, 森正人, 今田由紀子, 石井正好

大会講演予講集　94　101-101　2008
Publisher: 日本気象学会
A356 近未来地球温暖化予測実験 : 十年スケール自然変動の精度よい予測を目指して(予測可能性,スペシャル・セッション「データ同化と予測可能性」II)

望月崇, 石井正好, 木本昌秀, 近本喜光, 渡部雅浩, 安中さやか, 坂本天, 塩竈秀夫

大会講演予講集　94　100-100　2008
Publisher: 日本気象学会
P320 日本の冬季気温の経年変動とその大規模大気循環場との関係

安中さやか, 花輪公雄

大会講演予講集　93　431-431　2008
Publisher: 日本気象学会
P438 日本の夏季気温場の経年変動と大気循環場

安中さやか, 花輪公雄

大会講演予講集　89　464-464　2006
Publisher: 日本気象学会
P161 日本の冬季・夏季気温場の卓越モードと大気大循環場および海面水温場との関係

八木晃司, 安中さやか, 木津昭一, 花輪公雄

大会講演予講集　87　315-315　2005
Publisher: 日本気象学会
レジームシフトの季節発展 (神戸コレクション--デジタル化と研究の展望)

安中さやか, 花輪公雄

海洋　35　(11)　798-803　2003/11
Publisher: 海洋出版
ISSN： 0916-2011
D159 レジームシフトの季節発展(歴史的海上気象観測データ(神戸コレクション)のデジタル化と研究の展望)

安中さやか, 花輪公雄

大会講演予講集　83　197-197　2003
Publisher: 日本気象学会
北半球海面水温場に見出されたレジームシフト : 熱帯太平洋との関係

安中さやか, 花輪公雄

大会講演予講集　82　51-51　2002/10/09
北半球海面水温場の長期変動特性--北極振動との関連 (総特集大規模大気海洋相互作用--数十年スケール変動の実態と機構) -- (3章北極海セクターにおける長期変動)

安中さやか, 花輪公雄

号外海洋　(24)　149-156　2001
Publisher: 海洋出版
ISSN： 0916-8575
沿岸水温資料を用いた歴史的海面水温資料の補正の検討 (特集デジタル化されたKobe Collection)

花輪公雄, 安中さやか

海洋　31　(7)　415-422　1999/07
Publisher: 海洋出版
ISSN： 0916-2011

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Books and Other Publications 1

レジームシフト－気候変動と生物資源管理－

川崎健, 花輪公雄, 谷口旭, 二平章

成美堂出版　2007

ISBN: 9784425531011

Presentations 15

Subsurface chlorophyll-a in the tropical Pacific

Sayaka Yasunaka

El Niño-Southern Oscillation: Past, Present, and Future　2025/03/14
CO2 uptake in the Arctic Ocean Invited

Sayaka Yasunaka

SAS webinar　2024/11/18
Pathways to an integrated understanding of the marine environment and marine ecosystems in Asia-Pacific Region

Sayaka Yasunaka, Hanani Adiwira, Jamie Kass, Toshio Suga

ICTCRED2024　2024/09/24
CO2 uptake in the Arctic Ocean Invited

Sayaka Yasunaka

2024/05/30
Marine Environment Integrative Analysis −from coast to world ocean, from seasonal to 10,000 year scale− Invited

Sayaka Yasunaka

JpGU2024　2024/05/27
琉球列島周辺海域における高水温イベントとサンゴ白化

安中さやか, 栗原晴子, 土井威志

JpGU2024　2024/05/26
海洋表層生物地球化学パラメータの広域分布と季節経年変動 Invited

安中さやか

大槌シンポジウム　2023/08/23
データの蓄積が明らかにする海洋環境変化 Invited

安中さやか

BBNJ協定の下での海洋遺伝資源のアクセスと利益配分　2023/07/29
An assessment of CO2 uptake in the Arctic Ocean from 1985 to 2018

Yasunaka, S, Manizza, M, Terhaar, J, Olsen, A, Yamaguchi, R, Landschutzer, P, Watanabe, E, Carroll, D, Adiwara, H, Muller, J. D, Hauck, J

JpGU2023　2023/05/24
An assessment of CO2 uptake in the Arctic Ocean from 1985 to 2018

Yasunaka, S, Manizza, M, Terhaar, J, Olsen, A, Yamaguchi, R, Landschutzer, P, Watanabe, E, Carroll, D, Adiwara, H, Muller, J. D, Hauck, J.

EGU2023　2023/04/24
北極海CO2吸収

安中さやか

低温研共同利用研究集会　2023/02/27
データの蓄積が明らかにする海洋環境変化

安中さやか

国連海洋科学の10年シンポジウム　2023/02/21
熱帯域における生物地球化学パラメータの分布変動

安中さやか

日本海洋学会 2022年度秋季大会　2022/09/07
Data accumulation reveals changes in the ocean environment

Sayaka Yasunaka

Ocean Decade Laboratories | A Productive Ocean　2022/06/01
クロロフィルa亜表層極大の広域分布と BGC Argoによる今後の研究展開 Invited

安中さやか

JpGU2022　2022/05/24

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Research Projects 11

海洋積算高水温の発生維持機構とその予測可能性

安中さやか

Offer Organization: 日本学術振興会

System: 科学研究費助成事業基盤研究(C)

Category: 基盤研究(C)

Institution: 東北大学

2023/04 - 2027/03
逆推定法を利用した太平洋大規模循環・変動と沿岸水の関わりの解明

Category: Grant-in-Aid for Transformative Research Areas (A)

2022/06 - 2027/03
海洋課題北極海環境動態の解明と汎用データセットの構築 Competitive

Watanabe Eiji, Ueno Hiromichi, Itoh Motoyo, Kimura Satoshi, Zhang Yuanxin, Yasunaka Sayaka, Hatta Mariko, Nakajima Ryota, Ikenoue Takahito, Murata Akihiko, Shigemitsu Masahito, Noguchi Maki, Nishino Shigeto, Onodera Jonaotaro, Fujiwara Amane, Sugie Koji, Kimoto Katsunori, Kitamura Minoru, Abe Hiroto, Matsuno Kohei, Kasai Akihide, Kawakami Tatsuya, Nomura Daiki, Hirata Takafumi, García Molinos Jorge、Alabia Dolorfino Irene, Ohshima Keiichiro, Nishioka Jun, Kameyama Sohiko, Yamamoto Masanobu, Hirawake Toru, Ito Masato, Harada Naomi, Shiozaki Takuhei, Kawaguchi Yusuke, Kodaira, Tsubasa、Mizobata Kohei, Kawai Michiyo

Offer Organization: Ministry of Education, Culture, Sports, Science and Technology

System: ArCS II: Arctic Challenge for Sustainability II

Institution: 国立極地研究所、海洋研究開発機構、北海道大学

2022/04 - 2025/03
北極海におけるCO2吸収量の長期変化傾向

安中さやか

System: 科学研究費補助金（基盤C）

2020/04 - 2023/03
気候変動が引き起こす海洋溶存酸素変化：データ解析と数値計算による総合研究

見延庄士郎

System: 科学研究費補助金（基盤A）

2018/04 - 2023/03
漂流ブイによる海洋表層CO2分圧の中長期モニタリング観測‐データ空白域の解消を目指して‐ Competitive

村田昌彦

Offer Organization: 環境省

System: 地球環境保全試験研究費

2016/04 - 2021/03
太平洋の広域観測データに基づく新たな窒素固定モデルの開発 Competitive

橋岡豪人

Offer Organization: 東京大学

System: 学際連携研究

2016/04 - 2017/03
生元素循環および生態系の長期変動解明 Competitive

千葉早苗

System: 科学研究費補助金（新学術）

2014/04 - 2016/03
大気海洋結合大循環モデルで再現された十年規模変動とその予測可能性 Competitive

安中さやか

Offer Organization: 日本学術振興会

System: 科学研究費補助金（特別研究員奨励費）

Category: 特別研究員奨励費

2009/04 - 2012/03

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XBT(Expendable Bathythermograph:投下式水温水深計)による海水温観測値に内在していたバイアスの、大気海洋結合大循環モデル(MIROC3)を用いた気候変動予測に対する影響を調べた。バイアスを除去した観測値の全球平均表層水温に見られる長期変化は、太陽放射や温室効果ガスの濃度を外部条件として与えて計算したモデル(MIROC3)による海水温長期変化の結果とよく一致した。さらに、バイアスを除去した観測値を初期値として用いた気候変動予測は、バイアスを除去しない観測値を用いた予測に比べて、太平洋10年規模変動(PDO)の予測可能性を向上させることがわかった。海面水温(SST)は、全球規模で長い時系列を用意できる海洋資料で、気候変動調査には非常に有効である。これまで格子化データセットを様々な機関が作成・公開しているが、特に、観測数の少ない期間や海域では、データセット間に差があることが知られている。しかし、1970年以前の比較検討は限定的であるので、気候変動研究に広く使われている歴史的SSTデータセットを相互比較した。また,統計値の比較だけでなく、気候シグナルの比較も行うとともに、その差の原因を考察した。その結果、元データや作成方浩の違いから、データセット間で大きな差があることがわかり、解析結果を解釈する際、各々のデータセットの特性を考慮し、必要に応じて、他のデータセットによる結果と比較すべきであると結論付けられた。過去100年間の海洋亜表層水温の昇温パターンを調べた。5年移動平均をかけた1911～2010年の年平均SST偏差に対してEOF解析を行ったところ、第1モードとして、揺らぎながらも単調に増加する時係数と、ほぼ全域で正の値を示す空間パターンが得られた。これに対応して、亜表層水温場は、亜熱帯域における大きな昇温と北太平洋亜寒帯域における局所的な負のトレンドを示し、大気循環場は、極域における海面気圧の低下と偏西風の強化および貿易風の時弱化が見られた。
全球大気海洋系における卓越変動の季節発展と海洋亜表層の役割 Competitive

安中さやか

Offer Organization: 日本学術振興会

System: 科学研究費補助金（特別研究員奨励費）

Category: 特別研究員奨励費

Institution: 東京大学

2007/04 - 2009/03

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日本の冬季気温の経年変動を,大規模大気循環場との関係に着目して考察した.日本の地点気温に対する回転主成分分析により,北西季節風の強さと関連する二つの卓越した変動パターンが抽出された.第1モードは,本州および南西諸島の気温変動を表すモードだった.風による温度移流の効果が気温偏差と関連することが示唆される一方,本州太平洋側の日照時間は,気温が低いときに長い傾向があった.また,大規模循環場との関係を調べたところ,WPパターンを伴っており,ENSOと関係することがわかった.第2モードは,北日本の気温変動を表し,1988/89年に大きな変化を示した.温度移流の効果が気温偏差と関連することが示唆されたが,日照時間との相関は低かった.また,対応する大気循環場のパターンは,北極振動に類似していた. 大気海洋結合大循環モデルに見られる太平洋十年規模変動を調べた.ENSOに関連する数年周期とともに、10〜30年の周期帯にもスペクトルピークを持つ変動が存在していた.Decadalスケールの変動は,ENSOスケール変動によく似た時空間特性を持っている一方,赤道西部に貯まった水温偏差の東進速度が異なることで,両者の変動周期の違いが生じたと考えられる.また,東進速度の違いにより,ENSOスケールの変動とDecadalスケール変動の特性の違いを推察することができた.
全球海面水温場に出現するレジームシフトとその季節依存性 Competitive

安中さやか

Offer Organization: 日本学術振興会

System: 科学研究費補助金（特別研究員奨励費）

Category: 特別研究員奨励費

Institution: 東北大学

2003/04 - 2006/03

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レジームシフトがいつ起こり,その前後でどのような変化が起こったのかを,海面水温(SST)場に着目して調べた.また,気圧や風の格子化データを用いて,SST変動に伴う大気循環場の変動を明らかにした.さらにレジームシフトとSST場の卓越変動モードやENSOイベントとの関係についても調べた. その結果,1910年代から1990年代にかけて、計5回のレジームシフトが全球スケールで起こっていたことがわかった.それらは,以前の研究において,北半球で見出されたレジームシフトのうち、熱帯変動を伴うものと一致していた.次に,レジームシフトとENSOイベントとの関係を調べたところ,すべてのシフトは,ENSOイベントの発生と同期して起こっていたことがわかった.すなわち,レジームシフトの起こったとき,熱帯太平洋のSSTは,ラ・ニーニャ(エル・ニーニョ)の状態からエル・ニーニョ(ラ・ニーニャ)の状態へ1年で遷移していた.これらのENSOイベントは,7-9月期に始まり,翌年の1-3月期に成熟期に達した後,翌年まで持続するという特徴的な季節発展を示していた.一方,レジームシフトに伴うSSTの変化は,ENSOイベントのものと比べ,1-3月期の北太平洋や北大西洋において顕著であった.また,それらの変化は,ほとんどの海域で,次のシフトまで持続していた.EOF解析により,全球SST場に卓越する変動パターンを抽出したところ,4つのモードが得られた.すなわち,1年を通して卓越するENSOモードと南半球トレンドモード,および,1-3月期に北半球で卓越する北太平洋モードと北極振動モードである.北半球と同様,全球規模においても,ENSOモード,北太平洋モードと北極振動モードが,レジームシフトに伴い,同期した有意な位相反転を示した.すなわち,北半球1-3月期においては,複数モードの同時符号反転があったために,ENSOイベントに伴う変化より大きな変化が見られたものと考えられる.また,北太平洋モードの符号反転は,熱帯太平洋西部における高気圧性(もしくは低気圧性)の大気循環をもたらし,レジームシフトに同期したエル・ニーニョ(ラ・ニーニャ)の終息を抑制する働きをしたことが示唆される. これらの成果はアメリカで開催されたワークショップや日本海洋学会ならびに日本気象学会で発表されるとともに,国際学会誌International Journal of Climatologyに掲載された.

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