The response of calcareous nannofossil Eprolithus floralis to Oceanic Anoxic Event 2 (Cenomanian-Turonian, Late Cretaceous)

Oceanic Anoxic Event 2 (OAE 2; Cenomanian–Turonian) is an interval of environmental perturbation associated with elevated CO₂, linked to the activity of the Caribbean Large Igneous Province. It represents a natural experiment for investigating the response of marine organisms, including calcareous nannoplankton, to extreme oceanic disruption. This study focuses on Eprolithus floralis, a nannolith with cooler surface water affinity. Previous morphometric analyses documented size and morphological changes of E. floralis across OAE 2 in the Eastbourne section (UK). To assess whether this signal is global and to explore the drivers, we investigated the size, morphology, and abundance of E. floralis across: Clot Chevalier (France), Novara di Sicilia (Italy) -up to peak B- and Tarfaya (Morocco). Our results indicate that the morphometric and morphological response of E. floralis to OAE 2 consist of reproducible signals, although modulated by local paleoceanographic conditions. A reduction in mean total diameter during OAE 2 is observed in all sections, with minimum values at peak B of the δ¹³C, or slightly later at Tarfaya. Only at Novara di Sicilia E. floralis displays reduced dimensions prior to OAE 2. A post-OAE 2 size increase is observed in all records. Two morphotypes, spiky and rounded previously identified at Eastbourne, occur in all studied sections and show broadly similar patterns thus excluding a diagenetic control on nannolith morphology. Rounded E. floralis increases in abundance immediately prior to the onset of OAE 2 and dominates throughout the event (>50%), whereas spiky forms prevail in pre- and post-OAE 2 intervals. The spiky morphotype is larger than the rounded morphotype and, consequently, variations in total mean size reflect changes in morphotype dominance. Interestingly, the size offset between morphotypes varies geographically, being smaller at Eastbourne and Clot Chevalier (ca.0.2 μm) and larger at Novara di Sicilia and Tarfaya (ca.0.5 μm). No correspondence is observed between E. floralis size or abundance with the Plenus Cold Event, suggesting that temperature was not a primary control. Notably E. floralis is more common at Novara di Sicilia and Tarfaya possibly due to different oceanographic settings, being the two sections located in upwelling areas. We conclude that E. floralis responded globally to OAE 2 with size reduction and change in dominance of morphotype abundance. Size variation is comparable to that documented in Biscutum constans coccoliths. This correspondence suggests a common sensitivity to peak environmental stress, potentially linked to elevated CO₂ levels and increased concentrations of toxic trace metals. Importantly, regional variability provides insights into the adaptive strategies of E. floralis. The predominance of smaller, rounded morphotypes at Novara di Sicilia and Tarfaya suggests a preference for unstable conditions, such as those of upwelling. We speculate that the rounded morphotype may reflect a r-like strategy whereas the larger spiky were better adapted to more stable conditions.