Japan Geoscience Union Meeting 2018

Presentation information

[EE] Evening Poster

M (Multidisciplinary and Interdisciplinary) » M-IS Intersection

[M-IS01] Evolution and variability of Asian Monsoon and its linkage with Cenozoic global cooling

Mon. May 21, 2018 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Masanobu Yamamoto(Faculty of Environmental Earth Science, Hokkaido University), Ryuji Tada(Department of Earth and Planetary Science, Graduate School of Science, The Univeristy of Tokyo)

[MIS01-P02] Two step expansion of C4 plants in northwestern India at 10 Ma and 7.5 Ma: Evidence of leaf wax carbon isotopes in IODP Site U1457 sediments

Kenta Suzuki2, *Masanobu Yamamoto1,2, Osamu Seki2,3 (1.Faculty of Environmental Earth Science, Hokkaido University, 2.Graduate School of Environmental Sceince, Hokkaido University, 3.Institute of Low Temperature Science, Hokkaido University)

Keywords:C-4 plants, Miocene, India

Earlier studies indicated that C4 plants started to expand globally around 8 Ma (e.g., Cerling et al., 1997). This phenomenon is attributed to the decrease of atmospheric CO2 (Cerling et al., 1997), cooling (Zhang et al., 2003) and aridification (Huang et al., 2001).

In this study, we generated a record of the stable carbon isotope (δ13C) of higher plants during the last 10.6 m.y. Long-chain fatty acids (>26 carbons) were analyzed for 90 samples between 0 to 1000 m in Site U1457, Laxmi Basin, Arabian Sea.
The δ13C of C26, 28, 30 fatty acids was –29 ‰ at 10.5 Ma, dropped at 10 Ma to –34 ‰, recovered to –28 ‰ by 9 Ma, dropped again at 8 Ma to –33 ‰, abruptly increased to –26 ‰ at 7.5 Ma, gradually increased to –23 ‰ by ~6 Ma, and constantly high after 6 Ma. This result indicates that the proportion of C4 plants around 10 Ma and 8 Ma was significantly low, and C4 plants expanded two times at 10 Ma and 7.5 Ma. The first retreat of C4 plants around 10 Ma corresponded to a wet period in eastern Europe (Böhme et al., 2007), suggesting that higher precipitation increased C3 plants. The second retreat of C4 plants around 8 Ma is unexplained, but the recovery of C4 plants at 7.5 Ma coincided with global cooling, suggesting a drastic decrease of atmospheric carbon dioxide concentration may have induced C4 plant expansion.