共催：東京大学大気海洋研究所地球表層圏変動センター, PAGES, INQUA commission of Coastal and Marine Processes
今回は九州大学の中田正夫教授に
（１）地球回転とコアーマントル境界の物性についての固体地球物理についての研究成果
（２）現在進行中の氷床融解の知見について、潮位計データやステリックな海面変化を考慮した研究成果
について講演していただく予定です。
セミナー後には懇親会も予定しております。そちらもご参加ください。
日時：2012年10月30日 (Tue)
場所：東京大学 大気海洋研究所（アクセス） @219号室
時間割：15:00-16:00 講演１
16:00-16:30 休憩
16:30-17:30 講演２
17:45- 懇親会 (@217号室）
問い合わせ先：横山祐典（yokoyama AT aori.u-tokyo.ac.jp）
発表のタイトル、アブストラクトは以下の通りです。
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講演１：Viscosity structure of the D² layer inferred from the decay time of Chandler wobble and tidal deformation: Implications for the temperature and heat flow at the core-mantle boundary
Abstract
The viscosity structure of the D² layer of the Earth’s mantle is inferred from the decay time of the Chandler wobble and semi-diurnal to 18.6 years tidal deformations combined with model viscosity-depth profiles corresponding to a range of temperature-depth models. We use two typical temperature profiles of the D² layer by considering its dynamic state: (i) bottom thermal boundary layer of the mantle convection (TBL model) and (ii) vigorously small-scale convecting layer (CON model). Three possible models are derived from the comparison between the numerical and observationally inferred decay times of Chandler wobble and tidal deformation. The first and second models are those with a viscosity of ~1016 Pa s at the core-mantle boundary. The temperature gradient for the first one, TBL model with a thickness of the D² layer (L) of ~ 200 km, is nearly constant within the D² layer. The second one, TBL and CON models with L~300 km, requires that the temperature gradient of the lower part (~100 km thickness) is larger than that of the upper part. The temperature increases within the D² layer for these two models are larger than ~1500 K. The third model has a constant low viscosity layer (~100 km thickness and viscosity smaller than ~1017 Pa s) at the bottom of the D² layer in TBL (L~200 and 300 km) and CON (L~300 km) models. The temperature increases would be 1000-1600 K depending on the viscosity at the top of the D² layer (1021-1022 Pa s). The heat flows from the core to the mantle for these three models are estimated to be larger than ~5 TW. The third model may be preferable after comprehensively taking account of the fitness of the decay time of the Chandler wobble and the tidal deformations for each model.
References
Nakada, M. and Karato, S., 2012. Low viscosity of the bottom of the Earth’s mantle inferred from the analysis of Chandler wobble and tidal deformation. Physics of the Earth and Planetary Interiors, 192-193, 68-80.
Nakada, M., Iriguchi, C. and Karato, S., 2012. The viscosity structure of the D² layer of the Earth’s mantle inferred from the analysis of Chandler wobble and tidal deformation. Physics of the Earth and Planetary Interiors, 208-209, 11-24.
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講演２：Rates and causes of 20th century (pre-satellite era) sea-level rise
Abstract:
Relative sea-level (RSL) changes derived from tide gauge and/or salt-marsh sediment sequences, with information for RSL changes during at least the past ~200 years, are analyzed to examine the rates and the causes of the global sea-level rise (GSLR) in the twentieth century (pre-satellite era) by incorporating thermosteric sea-level and recent estimates for the melting of mountain glaciers and polar ice caps. In this study, we do not require the glacial isostatic adjustment (GIA) correction and only assume steady tectonic movements at RSL observation sites. We first estimate the acceleration of the 20th century sea-level rise at each observation site, and then evaluate the residual between the acceleration and thermosteric sea-level rise. The residuals are principally effective in examining the RSL changes caused by the melting of mountain glaciers and Antarctic and Greenland ice sheets. Consequently, we infer an equivalent sea-level rise (ESLR) of ~1.4 mm yr-1 for the melting of mountain glaciers, Antarctic and Greenland ice sheets, in which each contribution in ESLR corresponds to the maximum estimate of IPCC2007 report, i.e., 0.68, 0.55 and 0.17 mm yr-1, respectively. It would be worth noting that the contribution from the Greenland ice sheet is rather small compared with other two sources. Moreover, the present study indicates the global sea-level rise in the twentieth century before the rapid sea-level acceleration occurred at 1990 to be ~1.7 mm yr-1.
References
Nakada, M. and Inoue, H., 2005. Rates and causes of recent global sea-level rise inferred from long tide gauge data records. Quaternary Science Reviews, 24, 1217-1222
Nakada, M., Okuno, J. and Ishii, M., Twentieth century sea-level rise inferred long tide gauge, geologically derived and thermosteric sea-level changes (submitted to Quaternary Science Reviews).
