OCE-PRF: Windows into Cretaceous diatom paleobiology: Seasonal responses in laminated sediments and survivability and response to the Cretaceous-Paleogene extinction event

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Diatoms are photosynthetic algae that are an essential part of the biosphere and Earth’s climate system. While Cenozoic records indicate their impact on primary biological and chemical cycles, there is a lack of descriptive and applied research on Cretaceous diatoms. This lack of descriptive work limits their application for understanding ancient global ecosystems such as the Cretaceous greenhouse climates. Therefore, developing a better understanding of how diatoms responded to significant environmental perturbations during the end-Cretaceous mass extinction event and their response to seasonal changes in the early Cretaceous; is critical for understanding how Earth’s climate system has evolved through geologic time and helps constrain future climate variability. The unifying research theme is to better understand the controls on diatom responses to paleoenvironmental changes and improve their utility as tools for Cretaceous geological studies. PI Coenen will study modern and ancient laminated sediments to better understand Ocean Drilling Project Site 693 paleoenvironments and diatom taxonomy. This work will provide a critical understanding of early Cretaceous climate variability on a seasonal timescale, which will aid in the understanding of Earth’s climate system in a greenhouse world. Additionally, PI Coenen will study diatoms and silicoflagellates both before and after the Cretaceous-Paleogene (K/Pg) mass extinction to see how siliceous microfossils respond to environmental perturbations and understand what factors led to survivability in diatoms through this mass extinction event. As an NSF Postdoctoral Researcher, PI Coenen will mentor undergraduate student projects and learn how to mentor graduate level projects and run a research lab with Dr. Harwood. Additionally, PI Coenen will develop modules for an online Antarctic Geosciences course and a Paleogene and Cretaceous siliceous microfossil biostratigraphy workshop. PI Coenen will also host outreach activities at local libraries and k-12 schools and work closely with UNL to foster efforts to broaden participation in the geosciences.The proposed research seeks to develop new information on diatom paleobiology and paleoecology from two locations in the Southern Hemisphere, ranging in time from the early Cretaceous through the K/Pg mass extinction event. PI Coenen will evaluate whether modern ecological approaches can be applied to ancient paleontological records. The central hypothesis is that Cretaceous diatoms shared many life strategies with modern diatoms, allowing for the application of ‘biological uniformitarianism’ to interpret fossil diatom records. This research will be conducted at the University of Nebraska-Lincoln, where Dr. Harwood will mentor PI Coenen on Cretaceous diatom systematics, biostratigraphy, and paleoecology. Drs. Harwood and Coenen will collaborate with Dr. Leventer to provide Coenen training on modern diatom-bearing laminated sediments from the East Antarctic margin to build his skill set to interpret early Cretaceous diatom seasonal changes from ODP Site 693 laminations. This work will provide a rare opportunity to study high-resolution ocean-atmospheric forcing during early Cretaceous greenhouse climates. Additionally, siliceous microfossils from Seymour and Vega islands, Antarctic Peninsula, will be documented across a precursor extinction recognized in the macrofauna ~150 kyr prior to the K/Pg mass extinction event, as well as document the post-event recovery. The response of both silicoflagellates and diatoms to extreme environmental perturbations will be studied in detail to document silicoflagellate retrograde evolution and better understand how diatoms survived the K/Pg extinction that decimated other fossil phytoplankton. Study of diatom assemblages, with a focus on abundance and volume changes of diatom resting spores across a potential precursor extinction related to the Deccan Traps will provide data to resolve these questions. Additionally, this research on the newly forming Southern Ocean has important implications for understanding late Cretaceous paleoclimate and paleoceanography. Both proposed studies have the potential to constrain modeling efforts and provide a better sense of paleoenvironments in these respective intervals.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.