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- Title
Long-term response of oceanic carbon uptake to global warming via physical and biological pumps.
- Authors
Akitomo Yamamoto; Ayako Abe-Ouchi; Yasuhiro Yamanaka
- Abstract
Global warming is expected to significantly decrease oceanic carbon uptake and therefore accelerate an increase in atmospheric CO2 and global warming. The primary reasons in previous studies for the change in the oceanic carbon uptake are the solubility reduction due to seawater warming and changes in the ocean circulation and biological pump. However, quantifications of the contributions from different processes to the overall reduction in ocean uptake are still unclear. Herein, we investigate multimillennium response of oceanic carbon uptake to global warming and quantify the contributions of the physical and biological pump to the response using an atmosphere-ocean general circulation model and a biogeochemical model. We found that global warming reduced oceanic CO2 uptake by 13 % (30 %) in the first 140 years (at year 2000), which is consistent with previous studies. Sensitivity studies show that changes in the biological pump via ocean circulation change and solubility change due to seawater warming are dominant processes in the uptake reduction. These results are contrary to most previous studies wherein circulation changes and solubility change from seawater warming are the dominant processes. The weakening of biological production and carbon export induced by lower nutrient supply diminishes the vertical gradient of DIC substantially reducing the CO2 uptake. The weaker deep-ocean circulation decreases the downward transport of CO2 from the surface to the deep ocean, leading to a drop in the CO2 uptake in high-latitude regions. Conversely, weaker equatorial upwelling reduces the upward transport of natural CO2 and therefore enhances the CO2 uptake in low-latitude regions. Because these effects cancel each other, the circulation change becomes a second-order process. Our results suggest that the biological pump plays a significant role in the future oceanic carbon uptake through natural carbon cycle.
- Subjects
CARBON dioxide in water; GLOBAL warming; SEAWATER; OCEAN circulation; CARBON cycle
- Publication
Biogeosciences Discussions, 2017, p1
- ISSN
1810-6277
- Publication type
Article
- DOI
10.5194/bg-2017-451