The recovery of calcareous nannoplankton following the Cretaceous-Paleogene (K-Pg) mass extinction event 66.0 million years ago
Open Access
- Author:
- Jones, Heather Louise
- Graduate Program:
- Geosciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 27, 2020
- Committee Members:
- Timothy Bralower, Dissertation Advisor/Co-Advisor
Timothy Bralower, Committee Chair/Co-Chair
Mark E Patzkowsky, Committee Member
Lee Kump, Committee Member
Todd C Lajeunesse, Outside Member
Mark E Patzkowsky, Program Head/Chair - Keywords:
- geology
geosciences
paleobiology
paleontology
micropaleontology
oceanography
paleoceanography
extinction
evolution
paleoecology
K-Pg
plankton
phytoplankton
calcareous nannoplankton
coccolithophores
morphometrics
fossils - Abstract:
- Anthropogenic activity is causing atmospheric carbon dioxide to increase at rates unprecedented in the geological record. The resulting rise in annual average temperatures, surface ocean acidification, eutrophication, and frequency of extreme weather events, is causing, and will continue to cause, species to adapt, migrate, or become extinct. Among the organisms that are likely to be particularly vulnerable to extreme environmental change are the calcareous nannoplankton, the most dominant calcifying phytoplankton in the surface ocean. These organisms are of great importance to the marine ecosystem as they are a major component of the ocean-atmosphere carbon cycle and provide an important food source to both planktic and benthic organisms. In this dissertation, I take advantage of the extensive and globally distributed fossil record of calcareous nannoplankton to determine the long-term, community-scale response to environmental change during the earliest Paleocene (~62 to 66 million years ago (Ma)). This interval is characterized by the ecological recovery of marine ecosystems following the mass extinction event at the Cretaceous-Paleogene (K-Pg) boundary ~66 Ma, which was almost unequivocally caused by a bolide impact in the Yucatán, Mexico. The post-impact environment at the K-Pg boundary shares many similarities with the modern ocean, providing us with an excellent opportunity to examine the response of calcareous nannoplankton to extreme environmental perturbation over geological timescales. The aim of this dissertation is to better understand the environmental and ecological drivers of calcareous nannoplankton recovery following their almost complete elimination at the K-Pg boundary, as well as the timescales over which their recovery occurred. In Chapter 2, I examine early Paleocene assemblage change in the peak ring of the Chicxulub impact crater, which likely represented the most hostile post-impact environment on Earth at that time. In Chapter 3, I continue my examination of post-impact community change at an expanded, distal continental shelf site (El Kef, Tunisia) which I then compare to the global record. Lastly, in Chapter 4, I conduct a time series analysis assessing changes in the size and shape of the extant nannoplankton genus Braarudosphaera, which survived the mass extinction event and became dominant in certain locations immediately after the impact. My results present two distinct lines of evidence (Chapters 2 and 3) suggesting that the taxa comprising nannoplankton “boom-bust” successions (a series of high dominance acmes) and the timing of the switchovers between acmes, differed depending on the marine environment studied (in particular, high vs. low nutrient environments) and the rate at which marine biological pump efficiency was restored. Meanwhile, my morphometric results (Chapter 4) indicate that the genus Braarudosphaera was able to rapidly diversify and adapt to changing environmental conditions, likely contributing to their survival at the K-Pg boundary and their continued evolutionary success. Therefore, the results of this dissertation have important implications in assessing the resilience of nannoplankton communities and the adaptive capabilities of certain taxa to modern environmental change.