Vital Effects and Ecologic Adaptation of Photosymbiont-Bearing Planktonic Foraminifera During the Paleocene-Eocene Thermal Maximum, Implications for Paleoclimate

Stable isotope-size data of four major planktonic foraminifera lineages from the Paleocene-Eocene Thermal Maximum (PETM, similar to 56Ma) at two locations (North Atlantic New Jersey shelf and Southern Ocean) are analyzed. By comparing changes in delta C-13/delta O-18-size correlation prior to and during the PETM, we present evidence of significant changes in vital effects in photosymbiont-bearing planktonic foraminifera during the PETM. The delta C-13-size data indicate divergent changes in delta C-13 vital effects in high-latitude versus mid-latitude populations, due likely to different responses in photosymbiotic activities. Combined delta O-18-size data and isotopic ranking indicates that some surface dwellers experienced changes that may be interpreted as depth migrations. Extreme temperatures (>32 degrees C) may have exerted selective pressure and drove depth migrations. Species with flexible depth distribution were capable of adapting to rapid warming by vertical migration in the upper ocean, while populations restricted to near-surface ocean may have undergone temporal and/or regional collapse during the peak warming. From a paleo-proxy perspective, these biologic responses have the potential to obscure paleoceanographic signatures both regionally and globally.