The largest extinction of deep-sea benthic foraminifera in the Cenozoic occurred during the Paleocene-Eocene Thermal Maximum event (PETM, ~55.8 Ma). Much has been speculated about the causes of such extinction, and proposed mechanisms include changes in productivity and/or oxygenation of bottom waters, metabolic changes and in the composition of the food supply to the seafloor, or the ocean acidification related to the massive input of isotopically light carbon into the ocean-atmosphere system, among others.
Here we analyse ocean acidification as a potential triggering mechanism of the extinctions. The early Eocene at the Zumaya section (Basque-Cantabrian Basin) is marked by a 4 m-thick interval with a very low CaCO3 content. In order to analyse whether CaCO3 dissolution had a direct effect on the extinctions across the PETM, we carried out dissolution experiments on various species of agglutinated benthic foraminifera from Zumaya. In general, agglutinated species that do not disappear in the interval of most intense dissolution at Zumaya were not -or only slightly- affected by our dissolution experiments, since they do not have calcareous particles or cement. However, some species that went extinct or locally disappeared during the early Eocene, such as Dorothia cylindracea, Spiroplectammina spectabilis and Haplophragmoides cf. walteri, are resistant to dissolution. These results suggest that, in addition to ocean acidification, other factors must have contributed to the destabilization of benthic foraminiferal assemblages.
Arreguín-Rodríguez G. J. & Alegret L., 2015. Experimentos de disolución de CaCO3 en foraminíferos bentónicos aglutinados del Paleoceno-Eoceno. Estudios Geológicos 71(1): e023. Article (in Spanish).
