Middle Eocene dinoflagellate cyst distribution in the southwestern Atlantic Ocean: paleoclimatic and paleoceanographic implications

GUERSTEIN, G.R.; GONZÁLEZ ESTEBENET, M.S.; DANERS, G.; PREMAOR, E. ; FERREIRA, E.P. ; BELGABURO, A.

Mendoza

Congreso; IV INTERNATIONAL PALAEONTOLOGICAL CONGRESS; 2014

International Palaeontological Association

The Middle Eocene dinoflagellate cyst organic walled assemblages from Southwest Atlantic basins are represented by Antarctic-endemic components including species of Enneadocysta, Deflandrea, Vozzhennikovia, Spinidinium and Arachnodinium. In sections from Southern Hemisphere high latitudes (~50°S) the Middle Eocene Climatic Optimum (MECO) corresponds with an increase of Enneadocysta dictyostila (Menéndez) Fensome et al. Based on its positive correlation with CaCO3 percentages we assume that this form is the unique member of the endemic assemblage apparently tolerant to warm surface waters. This assumption is consistent with a significant representation of Enneadocysta dictyostila in samples from Colorado (~38°S), Punta del Este (~36°S), Pelotas (~30°S), Jequitinhonha (~17ºS) and Sergipe (~11°S) basins. Previous research developed in the Tasman area has related the presence of endemic taxa at mid latitudes to a strong clockwise subpolar gyre (?cold trap?) favoured by the continental blockage of the Tasmanian Gateway. We propose that the dinoflagellate cyst distribution in the Southwest Atlantic basins can be explained by a similar dynamical mechanism forming a proto- Weddell Gyre. Results from climatic model simulations indicate that the blockage of the Tasmanian Gateway and a partially-open Drake Passage both contributed to the formation of a strong western-intensified clockwise gyre. Morever, the same simulations showed that the gyre intensified after the MECO. Therefore, we hypothesize that during the MECO the species tolerant to warm waters flourished in high latitudes, while the subsequent drop of temperature intensified the proto-Weddel Gyre and transported the endemic components northward along the Southwestern Atlantic Shelf.