DIFFERENTIAL STABLE ISOTOPIC RESPONSE IN PLANKTONIC FORAMINIFERA FROM THE PALEOCENE-EOCENE THERMAL MAXIMUM, NEW JERSEY COASTAL PLAIN

The Paleocene-Eocene Thermal Maximum (PETM) was an abrupt warming event, characterized by a global temperature increase of about 5-8°C. The PETM is associated with the Carbon Isotope Excursion (CIE) represented by a decrease in δ¹³C values in marine (~2-3 ‰ in benthic and ~2.5-4 ‰ in planktonic foraminifera) and terrestrial (~2.5-6 ‰) environments. Here, we present stable isotope records of planktonic foraminifera across the onset of the PETM/CIE in the Millville New Jersey coastal plain core (ODP Leg 174AX). We analyzed multiple species of surface dwelling foraminifera (Morozovella spp., Acarinina spp.) and thermocline dwelling foraminifera (Subbotina spp.) for δ¹⁸O and δ¹³C. Our analyses show different responses to the PETM in surface versus thermocline species. The surface dwellers record a decrease in δ¹⁸O values of 1 ‰, whereas the thermocline dwelling Subbotina spp. record Δδ¹⁸O of -2 ‰. For carbon isotopes, Δδ¹³C in Morozovella spp. and Acarinina spp. are -4.5 ‰ and -4 ‰, respectively, while Subbotina spp. show change in δ¹³C values of -3.5 ‰. Two effects are proposed to explain such specific responses in the surface and thermocline dwelling planktonic foraminifera: 1) change in habitat of the surface dwellers due to intense acidification of the mixed layer and 2) non-uniform alteration of surface versus thermocline waters during the PETM. In the first case, the mixed layer in contact with the PETM atmosphere was more corrosive forcing surface dwellers to descend into the more buffered thermocline waters. As a result, Morozovella spp. and Acarinina spp. δ¹⁸O values record the PETM warming minus the change in habitat cooling. Accordingly, δ¹³C values reflect the whole ocean decrease plus change in habitat. In the second case, the PETM warming affected the surface and thermocline differently with twice the warming in the thermocline relative to the surface.