Symbiont 'bleaching' in planktic foraminifera during the Middle Eocene Climatic Optimum

TitleSymbiont 'bleaching' in planktic foraminifera during the Middle Eocene Climatic Optimum
Publication TypeJournal Article
Year of Publication2013
AuthorsEdgar KM, Bohaty SM, Gibbs SJ, Sexton PF, Norris RD, Wilson PA
Date Published2013/01
Type of ArticleArticle
ISBN Number0091-7613
Accession NumberWOS:000313026200004
Keywordsdelta-c-13; delta-o-18; evolution; globigerinoides-sacculifer; isotopes; life processes; paleocene thermal maximum; paleoecology; photosymbiosis; photosynthesis

Many genera of modern planktic foraminifera are adapted to nutrient-poor (oligotrophic) surface waters by hosting photosynthetic symbionts, but it is unknown how they will respond to future changes in ocean temperature and acidity. Here we show that ca. 40 Ma, some fossil photosymbiont-bearing planktic foraminifera were temporarily 'bleached' of their symbionts coincident with transient global warming during the Middle Eocene Climatic Optimum (MECO). At Ocean Drilling Program (ODP) Sites 748 and 1051 (Southern Ocean and mid-latitude North Atlantic, respectively), the typically positive relationship between the size of photosymbiont-bearing planktic foraminifer tests and their carbon isotope ratios (delta C-13) was temporarily reduced for similar to 100 k.y. during the peak of the MECO. At the same time, the typically photosymbiont-bearing planktic foraminifera Acarinina suffered transient reductions in test size and relative abundance, indicating ecological stress. The coincidence of minimum delta O-18 values and reduction in test size-delta C-13 gradients suggests a link between increased sea-surface temperatures and bleaching during the MECO, although changes in pH and nutrient availability may also have played a role. Our findings show that host-photosymbiont interactions are not constant through geological time, with implications for both the evolution of trophic strategies in marine plankton and the reliability of geochemical proxy records generated from symbiont-bearing planktic foraminifera.

Short TitleGeology
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