Morphometric and morphological response of Eprolithus floralis to Oceanic Anoxic Event 2 (Cenomanian/Turonian, Late Cretaceous)

Understanding the response of calcareous nannoplankton to past environmental perturbations is critical for assessing the impact of paleoenvironmental changes on marine calcifiers. Here, we analyze the size, morphotype distribution, and abundance of Eprolithus floralis across Oceanic Anoxic Event (OAE) 2 at Clot Chevalier (SE France), Novara di Sicilia (S Italy), and Tarfaya (Morocco), and compare them with Eastbourne (UK) to distinguish supra-regional from local environmental controls. Mean total diameter differs by ~1 μm between northern and southern sections and decreases from pre-OAE 2 to OAE 2, with minimum mean values generally reached around peak B of the carbon-isotope excursion. The magnitude of this decrease varies among sections, reflecting different regional baseline conditions. Rounded specimens are on average ~0.58 μm smaller than spiky specimens, and their increased relative abundance during OAE 2 contributes to the observed size decrease. Specimens with lowest size (3.2–3.5 μm) are extremely rare, suggesting a possible minimum size for the species. The magnitude of the morphometric response differs among sections, with the largest size reductions during OAE 2 at Clot Chevalier (16%) and Tarfaya (10%) and most complete post-OAE 2 recovery recorded at the northern localities, which also display the largest pre-OAE 2 average size. Neither temperature nor nutrient availability explains the common morphometric evolution observed across the four localities. Instead, the temporal correspondence between volcanism, atmospheric CO₂ increase and the onset, maximum size decrease and recovery, suggests that perturbations of the marine carbonate system exerted a control on coccolithophore calcification.