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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/cp-2019-31
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/cp-2019-31
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 07 Mar 2019

Research article | 07 Mar 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Glacial CO2 decrease and deep-water deoxygenation by iron fertilization from glaciogenic dust

Akitomo Yamamoto1,2, Ayako Abe-Ouchi1,2, Rumi Ohgaito1, Akinori Ito1, and Akira Oka2 Akitomo Yamamoto et al.
  • 1Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
  • 2Atmospheric an Ocedn Research Institute, The University of Tokyo, Kashiwa, Japan

Abstract. Increased accumulation of respired carbon in the deep ocean associated with enhanced efficiency of the biological carbon pump is thought to be a key mechanism of glacial CO2 drawdown. Despite greater oxygen solubility due to sea surface cooling, recent quantitative and qualitative proxy data show glacial deep-water deoxygenation, reflecting increased accumulation of respired carbon. However, the mechanisms of deep-water deoxygenation and contribution from the biological pump to glacial CO2 drawdown have remained unclear. In this study, we report the significance of iron fertilization from glaciogenic dust for glacial CO2 decrease and deep-water deoxygenation using our numerical simulation, which successfully reproduces the magnitude and large-scale pattern of the observed oxygen changes from the present to Last Glacial Maximum. Sensitivity experiments reveal that physical changes (e.g., more sluggish ocean circulation) contribute to only half of all glacial deep deoxygenation, whereas the other half is driven by enhanced efficiency of the biological pump. We found that iron input from the glaciogenic dust with higher iron solubility is the most significant factor for enhancement of the biological pump and deep-water deoxygenation. Glacial deep-water deoxygenation expands the hypoxic waters in the deep Pacific and Indian Ocean. The simulated global volume of hypoxic waters is nearly double the present value, which suggest that the glacial deep-water is sever environment for the benthic animals. Our model underestimated the deoxygenation in the deep Southern Ocean due to enhanced ventilation. The model-proxy comparison of oxygen change suggest that the stratified Southern Ocean is required for reproducing oxygen decline in the deep Southern Ocean. Enhanced efficiency of biological pump contributes to decrease of glacial CO2 by more than 30 ppm, which is supported by the model-proxy agreement of oxygen change. Our findings confirm the significance of the biological pump in glacial CO2 drawdown and deoxygenation.

Akitomo Yamamoto et al.
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Short summary
Proxy records of glacial oxygen change provide constraints on the contribution of the biological pump to glacial CO2 decrease. Here, we report our numerical simulation which successfully reproduces records of glacial oxygen changes and shows the significance of iron supply from glaciogenic dust. Our model simulations clarify that the enhanced efficiency of the biological pump is responsible for glacial CO2 decline of more than 30 ppm and approximately half of deep ocean deoxygenation.
Proxy records of glacial oxygen change provide constraints on the contribution of the biological...
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