Using pH to understand species-specific coccolithophore dynamics: a multi-disciplinary approach

Thesis

Coccolithophores are fascinating organisms that play crucial roles in marine ecosystems. Their interaction with carbonate chemistry has garnered considerable attention because they act as marine calcifiers and have an impact on primary production. Changes in carbonate chemistry affect CO₂ availability for photosynthesis and influence coccolithophore physiology and biochemistry through pH. Moreover, alterations in carbonate chemistry impact calcium carbonate saturation states, thus affecting calcification. This thesis aims to understand species-specific responses through the multifaceted effects of carbonate chemistry. It explores how pH influences molecular processes and how these translate into global impacts through biogeochemical changes. Dilute batch cultures are used to demonstrate how shifts in carbonate chemistry affect the carbon and oxygen isotopic composition of coccolith calcite and organic matter. Additionally, isotopic fractionation is used to understand carbon residence times in the internal carbon pools of coccolithophore species. Proteomic analyses shed light on the cellular mechanisms driving physiological changes in coccolithophores, revealing variations among species from different ecological and geological backgrounds. Moreover, coccolithophore physiology under changing carbonate chemistry is compared to investigate potential impacts on major nutrient cycles. Among all scenarios, Chrysotila carterae shows the more unique responses, perhaps due to its characteristic cell biology and habitat. Coccolithus braarudii emerges as the most sensitive species among those studied, with pH changes drastically affecting cellular processes and inducing carbon limitation under low CO₂ conditions. Stable isotopes of Gephyrocapsa huxleyi indicate significant isotopic disequilibrium due to large carbon fluxes in and out of the cell, driven by its high surface area to volume ratio. However, the high adaptability of cellular processes in G. huxleyi enables it to acclimate to pH changes, reflected in minor variations in its elemental stoichiometry. This research highlights species-specific responses to changing seawater pH and sets an example for increasing diversity in future coccolithophore research.

Authors: Chauhan, N

• DOI: 10.5287/ora-2rmajab6r
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Subjects: Biogeochemistry