Size variation of Eprolithus floralis across Oceanic Anoxic Event 2 (Late Cretaceous) in the Eastbourne section

Morphometric analyses of Eprolithus floralis were conducted in the Eastbourne section (southeast England, UK) to quantify size changes of this nannofossil species across Oceanic Anoxic Event 2 (OAE 2; Cenomanian/Turonian boundary, ∼94 Ma). The total and inner diameters exhibit a reduction of 3 % and 2.4 %, respectively, relative to the overall mean size during OAE 2 with minimum values (∼1 μm smaller) occurring at carbon isotope peak B. A recovery of 8.4 % and 5.7 % in two distinct morphotypes were identified: the rounded morphotype is ca. 0.5 μm smaller than the spiky one and starts to be more abundant just prior to OAE 2. The spiky morphotype accounts for 61 % before and 56 % after OAE 2 where it also shows largest average sizes and the smallest diaphragm. Morphometric shifts coincide with the onset of intense volcanism from the Caribbean Plateau whereas the size increase parallels the decline in volcanic activity, suggesting a possible link between environmental recovery and morphological diversification. Size and abundance minima of E. floralis and Biscutum constans at peak B suggest a shared physiological response, likely reduced calcification, to maximum environmental stress and possibly ocean acidification. However, E. floralis shows earlier size recovery, indicating higher ecological tolerance. No clear correlation is found with the Plenus Cold Event, excluding temperature as a primary control of E. floralis abundance and size. • E. floralis shows size reduction during OAE 2. • Minimum sizes reached around peak b. • Two morphotypes are identified: rounded and spiky . • Rounded specimens are small and more abundant during OAE 2. • There is a link between the onset and end of volcanism and the observed size variations.