Forcings on Coccolithophore Evolution and Assemblage Changes

Marine microplankton play an integral role on Earth, not only in supporting entire ecosystems but also in affecting fundamental components of the climate system. However, our understanding of the factors driving microplankton evolution and assemblage changes is still incomplete. Here, I explore how marine microplankton responded to drivers such as subaerial volcanism and abrupt climate change, with a focus on coccolithophores—a calcifying marine phytoplankton group. Coccolithophore assemblage analysis of annually laminated sediments from the northeastern Arabian Sea spanning the last century reveals their sensitivity to changes in the Indian monsoon system and the El Niño–Southern Oscillation. I utilize this baseline information to assess the impacts of a volcanic supereruption and a warm interstadial–cold stadial climate transition on the marine ecosystem. Primary productivity (based on a coccolithophore proxy) significantly increased in the northeastern Arabian Sea for about 8–19 years after the ~74 ka Toba supereruption, best explained by cooling of the Asian landmass that strengthened the Indian winter monsoon. However, the coccolithophore assemblage after the Toba supereruption responded differently from the succeeding cold stadial, supporting the notion that the supereruption did not trigger the interstadial–stadial climate transition. In general, subaerial volcanism also appears to play an unexplored role in microplankton evolution over million-year and orbital (20–100 kyr) time scales. Over the last 50 Myr, contrasting correlations between diatom diversity (positive) and calcareous nannoplankton diversity (negative) to the frequency of volcanic eruptions and climate potentially relates to different ecological responses to ash fertilization, although the exact processes remain speculative. Over orbital time scales, microplankton datums and strong volcanic eruptions in the Quaternary seem to cluster temporally; for instance, the extinction of the calcareous nannoplankton species Discoaster brouweri, although diachronous within a time period of 170 ka, occurred about 10 kyr after the Huckleberry Ridge Tuff supereruption in the Pacific, possibly pointing to a direct impact of the supereruption on the extinction. In conclusion, this thesis underscores the overlooked role of volcanism on microplankton evolution and assemblage changes, which has important implications for our understanding of the complex interactions between solid Earth, climate, and the biosphere.

Department dc:contributor.department

Earth Sciences

Year dc:date.issued

2025

Author dc:creator

• Guballa, Jose Dominick Santos

Advisor dc:contributor.advisor

• Bollmann, Jörg

• coccolithophores
• ENSO
• monsoons
• Toba eruption
• volcanic eruptions

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc-nd/4.0/

Handle dc:identifier.uri

https://hdl.handle.net/1807/145038

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/145038