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| Titel |
Ocean circulation during the Middle Jurassic in the presence/absence of a circumglobal current system |
| VerfasserIn |
Maura Brunetti, Peter O. Baumgartner, Christian Vérard, Cyril Hochard |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250077412
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| Zusammenfassung |
| Pangea breakup started in the Early Jurassic by the formation of the Central Atlantic
and its connection with the Neotethys. By the Middle Jurassic, rifting between
North and South America may have opened a first marine proto-Caribbean passage.
However, the oldest known proto-Caribbean ocean crust is only of early Late Jurassic
age.
Based on earlier plate tectonic reconstructions featuring a wide open proto-Caribbean
seaway, the existence of a circumglobal equatorial current system has been suggested by
many authors as a possible physical mechanism for increasing the poleward ocean
heat transport, and hence, producing the reduced meridional temperature gradient
documented for the Middle Jurassic. Models with increased atmospheric pCO2,
estimated to be between 1 and 7 times pre-industrial values in the Jurassic, generate
elevated temperatures both in the tropics and in polar regions, but do not reduce the
meridional gradient. A different mechanism needs to be considered in order to reproduce
such reduced meridional temperature gradient. A possibility is enhanced poleward
heat transport through the ocean. However, this hypothesis has been questioned
by Late Jurassic simulations with a specified, reduced meridional gradient, which
showed that the required ocean heat transport is much smaller than in present-day
simulations.
We investigate the critical role of a Tethyan–Atlantic–proto-Caribbean passage with
respect to the Middle Jurassic ocean circulation by means of coupled ocean/sea-ice numerical
models based on detailed plate reconstructions of the oceanic realms. We perform
numerical experiments with an open/closed western boundary of the proto-Caribbean
basin and we discuss the water properties, the gyre transport and the overturning
meridional circulation for these different bathymetric configurations. For an open western
boundary, we find a trans-Pangean circumglobal current of the order of 1Â Sv, that
flows in the upper 300 m along the northern margin of the Central Atlantic and
proto-Caribbean basins. We discuss the consequences of such a modest current on the global
ocean circulation and on water stratification/low upwelling rates in the Central
Atlantic. We compare the predicted effects with a revised analysis of Middle Jurassic
oceanic sedimentary records from the proto-Caribbean and the Central Atlantic. |
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