Linkage of deep sea rapid acidification process and extinction of benthic foraminifera in the deep sea at the Paleocene/ Eocene transition

• Published in: Island Arc
• Main Authors: Kawahata, Hodaka, Nomura, Ritsuo, Matsumoto, Katsumi, Nishi, Hiroshi
• Other Authors: Japan Society for the Promotion of Science
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2015
• Subjects: Methane hydrate; Ocean acidification; Planktonic foraminifera
• Online Access: http://dx.doi.org/10.1111/iar.12106; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fiar.12106; https://onlinelibrary.wiley.com/doi/pdf/10.1111/iar.12106

Abstract O cean D rilling P rogram L eg 199 S ite 1220 provides a continuous sedimentary section across the P aleocene/ E ocene ( P / E ) transition in the carbonate‐bearing sediments on 56–57 Ma oceanic crust. The large negative δ 13 C shift in seawater is likely due to the disintegration of methane hydrate, which is expected to be rapidly changed to carbon dioxide in the atmosphere and well‐oxygenated seawater, leading to a reduction in deep‐sea pH . A pH decrease was very likely responsible for the emergence of agglutinated foraminiferal fauna as calcareous fauna was eliminated by acidification at the P / E transition at S ite 1220. The absence of the more resistant calcareous benthic foraminifera and the presence of the planktonic foraminifera at S ite 1220 is interesting and unique, which indicates that calcareous benthic foraminifera suffered greatly from living on the seafloor. Box model calculation demonstrates that, assuming the same mean alkalinity as today, p CO 2 must increase from 280 ppm to about 410 ppm for the calcite undersaturation in the deep ocean and for the oversaturation in the surface ocean during the P / E transition. The calculated increased p CO 2 coincides with paleo‐botanical evidence. The current global emission rate (∼7.3 peta (10 15 ) g C /y) of anthropogenic carbon input is approximately 30 times of the estimate at the P/E transition. The results at the P/E transition give an implication that the deep sea benthic fauna will be threatened in future in combination with ocean acidification, increased sea surface temperature and more stratified surface water.