Gastropod carbonate delta (super 18) O and delta (super 13) C values record strong seasonal productivity and stratification shifts during the late Eocene in England

High-resolution delta (super 18) O and delta (super 13) C measurements obtained from the gastropod Clavilithes macrospira provide the most detailed record of seasonal change in temperature (range approximately 14 degrees C), seawater chemistry, and bottom-water ventilation yet obtained from late Eocene strata (type Bartonian, ca. 40 Ma). The delta (super 18) O oscillations suggest a linear rate of long-term growth and rapid growth in spring-early summer. Coherence analysis shows that delta (super 13) C patterns vary from being closely in phase with respect to annual delta (super 18) O oscillations, to being antiphase, with a phase shift toward a spring, or more rarely, an autumnal delta (super 13) C peak. These patterns are attributed to unstable seasonal productivity and/or the development of a seston-rich bottom layer, in which the delta (super 13) C gradients arising from seasonal eutrophication were perturbed by spring storms. Such episodes may have led to the decline and extinction of oligotrophic marine biota with photosymbionts, including Nummulites, in the late Eocene.