title: State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling.
abstract: Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets.
authors.affiliation: National Institute of Polar Research, Research Organizations of Information and Systems, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.; Department of Polar Science, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.; Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan.
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authors.identifier: 0000-0003-1163-700X
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authors.affiliation: Atmosphere and Ocean Research Institute, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa 277-8568, Japan.; Japan Agency for Marine-Earth Science and Technology, 3173-25 Showamachi, Kanazawa, Yokohama, Kanagawa 236-0001, Japan.
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authors.identifier: 0000-0003-1745-5952
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authors.affiliation: National Institute of Polar Research, Research Organizations of Information and Systems, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.; Department of Polar Science, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.
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authors.identifier: 0000-0003-2533-320X
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authors.affiliation: National Institute of Polar Research, Research Organizations of Information and Systems, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.; Department of Polar Science, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.
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authors.affiliation: Graduate School of Environmental Studies, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan.
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authors.affiliation: National Institute of Polar Research, Research Organizations of Information and Systems, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.; Department of Polar Science, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.
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authors.affiliation: National Institute of Polar Research, Research Organizations of Information and Systems, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.
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authors.affiliation: National Institute of Polar Research, Research Organizations of Information and Systems, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.; Department of Polar Science, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.
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authors.affiliation: National Institute of Polar Research, Research Organizations of Information and Systems, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.; Department of Polar Science, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.
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authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Kita-19, Nishi-8, Kita-ku, Sapporo 060-0819, Japan.
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authors.affiliation: National Institute of Polar Research, Research Organizations of Information and Systems, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.; Department of Polar Science, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.
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authors.affiliation: National Institute of Polar Research, Research Organizations of Information and Systems, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.; Department of Polar Science, Graduate University for Advanced Studies (SOKENDAI), 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan.
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keywords: Antarctica ice sheet; Atlantic Meridional Overturning Circulation; abrupt climate change; climate model; ice core; paleoclimate