Evolutionary ecology of Early Paleocene planktonic foraminifera:Size, depth habitat and symbiosis

• Published in: Paleobiology
• Main Authors: Birch, Heather S., Coxall, Helen K., Pearson, Paul N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2012
• Subjects: Planktonic foraminifera
• Online Access: https://hdl.handle.net/1983/50cd1209-e4c5-413e-8932-aceb1c0c3eb5; https://research-information.bris.ac.uk/en/publications/50cd1209-e4c5-413e-8932-aceb1c0c3eb5; https://doi.org/10.1666/11027.1; http://www.scopus.com/inward/record.url?scp=84868138646&partnerID=8YFLogxK

The carbon stable isotope ( 13 C) composition of the calcitic tests of planktonic foraminifera has an important role as a geochemical tracer of ocean carbon system changes associated with the Cretaceous/Paleogene (K/Pg) mass extinction event and its aftermath. Questions remain, however, about the extent of 13 C isotopic disequilibrium effects and the impact of depth habitat evolution on test calcite 13 C among rapidly evolving Paleocene species, and the influence this has on reconstructed surface-to-deep ocean dissolved inorganic carbon (DIC) gradients. A synthesis of new and existing multispecies data, on the relationship between 13 C and 18 O and test size, sheds light on these issues. Results suggest that early Paleocene species quickly radiated into a range of depths habitats in a thermally stratified water column. Negative 18 O gradients with increasing test size in some species of Praemurica suggest either ontogenetic or ecotypic dependence on calcification temperature that may reflect depth/light controlled variability in symbiont photosynthetic activity. The pattern of positive 13 C test-size correlations allows us to (1) identify metabolic disequilibrium 13 C effects in small foraminifera tests, as occur in the immediate aftermath of the K/Pg event, (2) constrain the timing of evolution of foraminiferal photosymbiosis to 63.5 Ma, ∼0.9 Myr earlier than previously suggested, and (3) identify the apparent loss of symbiosis in a late-ranging morphotype of Praemurica. These findings have implications for interpreting 13 C DIC gradients at a resolution appropriate for incoming highly resolved K/Pg core records.