Japan Geoscience Union Meeting 2019

Presentation information

[J] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-CC Cryospheric Sciences & Cold District Environment

[A-CC26] Ice cores and paleoenvironmental modeling

Tue. May 28, 2019 1:45 PM - 3:15 PM 201B (2F)

convener:Ryu Uemura(University of the Ryukyus), Kenji Kawamura(National Institute of Polar Research, Research Organization of Information and Systems), Ayako Abe-Ouchi(Atmosphere and Ocean Research Institute, The University of Tokyo), Nozomu Takeuchi(Chiba University), Chairperson:Ayako Abe-Ouchi(東京大学大気海洋研究所), Sam Sherriff-Tadano(University of Tokyo)

2:00 PM - 2:15 PM

[ACC26-14] Reproduction of the increasing amplitude and period in the glacial cycles using a model incorporating diatomaceous activity.

*Tasuku Akagi1, Takahiro Hasegawa2 (1.Department of Earth and Planetary Sciences, Faculty of Science, Kyushu University, 2.Graduate School of Science, Kyushu University)

Keywords:the glacial cycles, amplitude and period, silicon cycling, diatom activity

The mode changes in the glacial cycle, smaller amplitudes with 20 kyr periods before 2.7 BP; medium amplitudes with 40 kyr periods between 2.70 and 1 Ma BP; greater amplitudes with around 100 kyr periods after 1 Ma BP, remain unanswered.

Carbon cycling is closely coupled with silicon cycling in the Earth surface. Oceanic silica is supplied from weathering of terrestrial matter, which depends on the atmospheric pCO2. The atmospheric pCO2, in turn, is influenced by the diatomaceous biological pump. Silicon can be a crucial driver of the Earth surface environment. Oceanic silica is removed by the burial of amorphous silica produced by diatoms. We have reported that the non-linear dissolution behavior of diatom frustules, where greater diatomaceous production tends to suppress dissolution of dissolved silica forming greater-sized frustule-aggregates.

Here we have developed a numerical model expressing the carbon and silicon cycling in the Earth surface, with diatomaceous biological pump and the non-linear dissolution behavior of diatom frustules being introduced.

The results of the model runs show interesting outcomes: when the amount of circulating carbon is reduced with time, both the amplitude and period of atmospheric pCO2increase with time. When the insolation changes by Milankovitch forcing were loaded on the model temperature, the mode changes are successfully reproduced.

We propose that the glacial cycles may be understood by the coupling of ice-sheet dynamics and change in the oceanic Si inventory.