Environmental changes across the upper Eocene to upper Oligocene of the southern Labrador Sea, DSDP Site 112

The Eocene Oligocene Transition (EOT) 34 million years ago (Ma), was characterized by a climate shift from a largely ice-free greenhouse world to an icehouse climate. The colder Oligocene period included several cooling episodes, defining the bases of a s-Atlantic region, some of these cooling episodes are associated with appearance intervals of the dinocyst species Svalbardella clausii, and Svalbardella cooksoniae.

Here we present newly generated dinocyst, calcareous nannofossil, XRF and TEX86 proxy records across the upper Eocene to upper Oligocene from DSDP Site 112, southern Labrador Sea (latitude 54°N; Cores 13 to 5). The studied cores penetrate a deep-sea pelagic succession representing an interval of ~40 to 26.5 Ma. Our study reveals major depositional changes in the region of Site 112 across the EOT, including a decrease in the relative abundance of oceanic dinocysts (Impagidinium spp.), a decrease in carbonate content, higher siliciclastic delivery and grain coarsening. Furthermore, in the early Chattian we observe a high abundance of the potentially cold-water dinocyst S. clausii (up to 16% of the total dinocyst assemblage), possibly related to the Oi-2b cooling event.

The preliminary results of micro-Fourier transform infrared (FTIR) spectroscopy (a method for identifying macromolecular cell compositions in algal cells, and thus nutritional ecologies) in three morphologically similar Eocene and Oligocene dinocyst taxa (S. clausii, S. cooksoniae and Palaeocystodinium golzowense) suggest that they had similar feeding strategies. However, subtle differences in the resulting FTIR spectra indicate some geochemical distinctions between them. The affinity of S. clausii to colder surface waters is tested by comparison of its distribution to the TEX86-derived sea surface temperature record.