Deep-sea ostracode turnovers through the Paleocene–Eocene thermal maximum in DSDP Site 401, Bay of Biscay, North Atlantic

Previous low resolution studies suggest that ostracodes, in contrast with deep sea foraminifera, largely survived the massive environmental changes of the Paleocene–Eocene thermal maximum (PETM). In a new high-resolution study from the continental slope (~ 1800 m paleodepth) NE Atlantic, we also find extensive survivorship of ostracode faunas, but this is accompanied by a temporary drop in species diversity and ecological diversity during the PETM. There are 12 common ostracode species before the PETM that are reduced to only two species at the same time as the benthic foraminiferal extinction event. All but three species reappear in the later parts of the PETM and statistical analysis suggests that most of the apparent “Lazarus” species might be found with sufficient sampling of PETM faunas. We find no evidence for an excursion fauna of ostracodes as has been detected in calcareous nannofossils, planktic foraminifera, and benthic foraminifera. However, the ostracode assemblages changed from a relatively diverse ecological assemblage before and after the PETM to one dominated by infaunal species typical of low oxygen conditions during the PETM. The absence of major extinction and the temporary nature of species disappearances are comparable to turnovers in shallow marine ostracodes and stands in sharp contrast to the ~ 50% species-level extinction in benthic foraminifers.