Evolution and paleobiology of Cenozoic planktonic foraminifera and coccolithophores

• Main Author: Si, Weimin
• Format: Text
• Language: unknown
• Published: No Publisher Supplied 2018
• Subjects: Planktonic foraminifera
• Online Access: https://dx.doi.org/10.7282/t3-8dwj-tp20; https://rucore.libraries.rutgers.edu/rutgers-lib/59233/

In this study, I have examined the micro- and macroevolutionary changes in planktonic foraminifera and coccolithophores on different timescales. I first studied the taxonomy, stratigraphy and evolution of the Middle Miocene planktonic foraminifera Fohsella, an iconic example of gradual morphologic evolution in marine planktonic species. In contrast to earlier studies that have focused on the gross morphology as embodied by the projection of the edge view of tests, I have analyzed multiple phenotypic traits of the evolving lineage and found that traits did not evolve in concert. The evolution of the lineage is a mosaic combination of different evolutionary modes for different traits, suggesting that interpretations based on “pure” morphologic and “overall shape” measurements, may significantly underestimate the dynamics of foraminiferal evolution. On shorter timescales, microfossils provide empirical evidence on adaptations of species to rapid ocean warming and acidification. I examined changes in vital effects in photosymbiont-bearing planktonic foraminifera during the Paleocene-Eocene Thermal Maximum (ca. 56 Ma). The δ13C-size data indicate divergent changes in δ13C vital effects in high- versus mid-latitude populations, due likely to different responses in photosymbiotic activities. Combined δ18O-size data and isotopic ranking indicates that some surface dwellers may have experienced depth migrations due to extreme sea surface temperatures. Species with flexible depth distribution were capable of adapting to rapid warming by vertical migration in the upper ocean, while populations restricted to near surface may have undergone temporal and/or regional collapse during peak warming. From a paleo-proxy perspective, biologic responses during the PETM have obscured palaeoceanographic signatures both regionally and globally. On multi-Myr scale, macro-evolutionary changes in planktonic calcifiers may have also affected the ocean’s carbonate budget. I examined the changes in carbonate accumulation, production and dissolution of planktonic foraminifera and coccoliths. Mass Accumulation Rate shows that carbonate accumulation has decreased significantly over the last 15 Myr even though carbonate preservation has improved. A further separation of the bulk carbonate into foraminiferal and coccolith fractions indicates relatively constant foraminiferal contribution over time but significantly higher coccolith production in the Miocene. Given the constraint of relatively small changes in the carbonate compensation depth, carbonate accumulation in the deep-sea has decreased, suggesting reduced alkalinity input to the ocean since the Middle Miocene.