Ecological stasis and saltation: species richness change in planktic foraminifera during the late Paleocene to early Eocene, DSDP Site 577

Abstract

Abstract A high resolution study of late Paleocene to early Eocene planktic foraminifera at DSDP Site 577 indicates the presence of three rapid faunal turnovers, or saltation events, with durations varying between 200–400 kyr and species turnover rates between 4–12 species/100 kyr. These saltation events are separated by slow faunal turnovers, or stasis intervals, with durations varying between 2.56–5.21 Myr and species turnover rates between 0.6–1.8 species/100 kyr. Each saltation event has different characteristics with disappearances equal to appearances in event T1, appearances dominate in event T2 that nearly double species richness, and primarily disappearances in event T3 that nearly halve species richness. Only event T2 near the P E boundary is associated with major and sudden environmental changes, as marked by a rapid warming in the deep ocean and high-latitude surface ocean and a negative excursion in carbonate δ13C values, that suggest a cause-effect relationship. The other two events occur during intervals of gradual environmental changes. We suggest that all three faunal events are triggered by the attainment of threshold conditions during the oceanic environmental changes. Threshold conditions may be attained through rapid environmental changes as in the case of event T2 near the P E boundary, or by gradual though cumulative environmental changes as appears to be the case in events T1 and T3. It is unclear, however, which environmental factors (e.g., temperature, salinity, nutrients, water-mass stratification) force rapid faunal turnovers or what role intrinsic biotic factors play.