Eocene circulation and dinoflagellate distribution in the Southwestern Atlantic Ocean

GUERSTEIN, G. RAQUEL, BRINKHUIS, H. DANERS, G.

Buenos Aires

Congreso; XII Reunión Argentina de Sedimentología; 2008

Asociación Argentina de Sedimentología

The study of Middle Eocene dinoflagellate assemblages from subtropical SW Atlantic basins shows the presence of well represented "Transantarctic Flora" (TF) defined by Wrenn and Beckman (1982). The TF, including Enneadocysta dictyostila (usually named Areosphaeridium diktyoplokum or Enneadocysta partridgei) has been widely recorded in Middle Eocene sections from Southern Hemisphere high latitudes. Its distribution in the circum-Antarctic realm during the Paleogene was recently analysed by Warnaar (2006). Peaks of E. dictyostila along with other TF components have been observed in samples from Colorado Basin (~38°S), Argentina and Punta del Este Basin (~36°S), Uruguay. Previous research in the Tasman area has related the presence of the TF at mid latitudes to the formation of a strong clockwise subpolar gyre ("refrigerator trap") favoured by the continental blockage of the Tasmanian Gateway (Huber et al., 2004). In this presentation we extend these studies showing that the observed dinoflagellate distribution in the SW Atlantic can be explained by a similar dynamical mechanism operating close to the present Weddel Gyre. The blockage of the Tasmanian Gateway and a partially-open Drake Passage both contribute to the formation of a strong western-intensified clockwise gyre that may have transported the TF components from the Antarctic continent, northward along the SW Atlantic Shelf during the Middle Eocene. The opening and deepening of the Tasmanian Gateway and Drake Passage and the subsequent development of the ACC current during the Oligocene disrupted the subpolar gyre and promote the extinction of the TF species. * FONCYT PICT 07-26057 – CONICET PIP 6416 Huber, M. Brinkhuis, H. Stickley, C. E., Döös, Sluijs, A. Warnaar, J. Schellenberg, S.A. and Williams, G.L. (2004) Eocene circulation of the Southern Ocean: Was Antarctica kept warm by subtropical waters? Paleoceanography, 19, PA4026, doi: 10.1029/2004PA001014. and Williams, G.L. (2004) Eocene circulation of the Southern Ocean: Was Antarctica kept warm by subtropical waters? Paleoceanography, 19, PA4026, doi: 10.1029/2004PA001014. Warnaar, J. (2006) Climatological implications of Australian-Antarctic separation. Universiteit Utrecht, unpublished PhD Thesis. 143 pp. (2006) Climatological implications of Australian-Antarctic separation. Universiteit Utrecht, unpublished PhD Thesis. 143 pp. Wrenn, J.H. and Beckman, S.W. (1982). Maceral, total organic carbon, and palynological analyses of Ross Ice Shelf Project site J9 cores. Science 216, 187-189. and Beckman, S.W. (1982). Maceral, total organic carbon, and palynological analyses of Ross Ice Shelf Project site J9 cores. Science 216, 187-189.