Photosymbiosis in planktonic foraminifera across the Paleocene–Eocene thermal maximum

• Published in: Paleobiology
• Main Authors: Shaw, Jack O., D'HAENENS, Simon, Thomas, Ellen, Norris, Richard D., Lyman, Johnnie A., Bornemann, Andre, Hull, Pincelli M.
• Other Authors: Shaw, Jack/0000-0002-2725-2334
• Format: Article in Journal/Newspaper
• Language: English
• Published: CAMBRIDGE UNIV PRESS 2021
• Subjects: Dickens; Pacific; Southern Ocean; Planktonic foraminifera
• Online Access: http://hdl.handle.net/1942/36282; https://doi.org/10.1017/pab.2021.7

Under stress, corals and foraminifera may eject or consume their algal symbionts ("bleach"), which can increase mortality. How bleaching relates to species viability over warming events is of great interest given current global warming. We use size-specific isotope analyses and abundance counts to examine photosymbiosis and population dynamics of planktonic foraminifera across the Paleocene-Eocene thermal maximum (PETM, similar to 56 Ma), the most severe Cenozoic global warming event. We find variable responses of photosymbiotic associations across localities and species. In the NE Atlantic (DSDP Site 401) PETM, photosymbiotic clades (acarininids and morozovellids) exhibit collapsed size-delta C-13 gradients indicative of reduced photosymbiosis, as also observed in Central Pacific (ODP Site 1209) and Southern Ocean (ODP Site 690) acarininids. In contrast, we find no significant loss of size-delta C-13 gradients on the New Jersey shelf (Millville) or in Central Pacific morozovellids. Unlike modern bleaching-induced mass mortality, populations of photosymbiont-bearing planktonic foraminifera increased in relative abundance during the PETM. Multigenerational adaptive responses, including flexibility in photosymbiont associations and excursion taxon evolution, may have allowed some photosym-biotic foraminifera to thrive. We conclude that deconvolving the effects of biology on isotope composition on a site-by-site basis is vital for environmental reconstructions. We thank B. Erkkila and M. Wint of the Yale Analytical and Stable Isotope Center, C. Charles at the UCSD Stable Isotope Laboratory, and D. Andreasen at the UCSC Stable Isotope Laboratory for help with isotopic analyses; G. Dickens and four anonymous reviewers for insightful comments which improved our article; and the International Ocean Discovery Program for samples from Sites ODP 1209, ODP 690, and DSDP 401. E.T. recognizes funding by National Science Foundation (NSF) OCE 1536611. P.M.H., S.D., and J.O.S recognize funding by NSF OCE 1536604 and a Sloan ...