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Titel |
Middle Eocene paleocirculation of the southwestern Atlantic Ocean, the anteroom to an ice-house world: evidence from dinoflagellates |
VerfasserIn |
G. Raquel Guerstein, Gloria Daners, Elbio Palma, Elizabete P. Ferreira, Eduardo Premaor, Cecilia R. Amenábar, Alexandra Belgaburo |
Konferenz |
EGU General Assembly 2016
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Medientyp |
Artikel
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Sprache |
en
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 18 (2016) |
Datensatznummer |
250129953
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Publikation (Nr.) |
EGU/EGU2016-10131.pdf |
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Zusammenfassung |
Middle Eocene dinoflagellate cyst organic walled assemblages from sections located in the
Antarctic Peninsula, Tierra del Fuego, Santa Cruz province and south of Chile are mainly
represented by endemic taxa, which are also dominant in several circum - Antarctic sites
located southern 45˚ S. Some members of this endemic Antarctic assemblage, including
especies of Enneadocysta, Deflandrea, Vozzhennikovia, and Spinidinium, have been
recognised in sites along the Southwest Atlantic Ocean Shelf at Colorado (∼38˚ S), Punta
del Este (∼36˚ S) and Pelotas (∼30˚ S) basins. Northern 30˚ S, at Jequitinhonha (∼17oS)
and Sergipe (∼11˚ S) basins, there is no evidence of the endemic Antarctic members,
except for Enneadocysta dictyostila, recorded in very low proportion. Based on its
positive correlation with CaCO3 percentages we assume that this species is the
unique member of the endemic assemblage apparently tolerant to warm surface
waters. Previous research developed in the Tasman area has related the presence of
endemic taxa at mid- latitudes to a strong clockwise subpolar gyre favoured by the
partial continental blockage of the Tasmanian Gateways and the Drake Passage.
In this work we propose that the dinoflagellate cyst distribution along the South
Atlantic Ocean Shelf can be explained by a similar dynamical mechanism induced
by a cyclonic subpolar gyre on the South Atlantic Ocean. The western boundary
current of this gyre, starting on the west Antarctic continental slope, would follow a
similar path to the present Malvinas Current on the Patagonian slope. Modelling and
observational studies at the Patagonian shelf-break have shown that a cyclonic western
boundary current promotes upwelling and intrusion of cold oceanic waters to the shelf
and intensifies the northward shelf transport. In a similar way we hypothesize that
during the Middle Eocene the western boundary current of a proto-Weddell Gyre
transported the circum-antarctic waters and the endemic components northward along the
Southwestern Atlantic Shelf. During the Late Eocene, the endemic component is
replaced by more diverse assemblages with bipolar markers of cooler, typical oceanic
species and an increased number of heterotrophic protoperidiniaceans. The opening
and deepening of the Tasmanian Gateway and Drake Passage and the subsequent
development of an incipient Antarctic Circumpolar Current during the Oligocene
disrupted the subpolar gyres and promote the extinction of the endemic species. |
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