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| Titel |
Marine Isotope Stages (MIS) 96-101: Glacial induced closure of the Panamanian Gateway |
| VerfasserIn |
Jeroen Groeneveld, Henry DeBey, Ed C. Hathorne, Stephan Steinke |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250039045
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| Zusammenfassung |
| We present combined Mg/Ca and δ18O measurements from ODP Site 1241 from the east
Pacific and ODP Site 999 from the Caribbean. The studied time interval covers the first major
glacial-interglacial cycles (MIS96-101) after intensification of Northern Hemisphere
Glaciation. Analyses were performed on the planktic foraminifers Neogloboquadrina
dutertrei and Globigerinoides sacculifer, representing water mass properties in the
thermocline and the mixed layer respectively. Data resolution is aimed to be able to resolve
millennial scale variations to constrain the changes in water mass conditions during
MIS96-101.
Aim of the study is to test the theory that the Panamanian Gateway temporarily closed
during glacial MIS 96, 98, and 100 due to a drop in sea level of 50-80 m. This
was first suggested in Groeneveld et al., (in prep.) and might have provided the
necessary conditions to allow the Great American Biotic Interchange, the large
scale migration of mammals from South to North America and vice versa. As this
exchange would have required more arid conditions in Central America to allow
the fauna, which was mainly adapted to a savannah-like environment, to cross, a
glacial period would have provided the right conditions. Reconstruction of sea water
temperatures can indicate if and when the gateway closed. With an open Panamanian
Gateway relatively cold water flowed from the Pacific into the Caribbean. With
the onset of glacial conditions sea surface temperatures (SST) expectedly would
show a decrease in the east Pacific (Site 1241). But, SSTs in the Caribbean (Site
999) are expected to rise as no longer relatively cold Pacific water is entering the
Caribbean, but rather the warmer waters from the Western Atlantic Warm Pool
advanced from the north to the core location. Indeed, reconstructed SSTs from G.
sacculifer show a decrease of 2.5Ë C at Site 1241 and an increase of 3Ë C at Site
999 suggesting that the Panamanian Gateway truly was closed during the glacial
stage.
Additionally, the Mg/Ca-temperatures of N. dutertrei, a thermocline dweller, do not show
any change in the east Pacific, but do show a 3Ë C cooling in the Caribbean. This suggests
that the closing of the gateway only influenced surface water conditions. The decrease in N.
dutertrei temperatures can be explained in two ways. With the closure the Western Atlantic
Warm Pool extended towards the southern Caribbean, increasing sea surface temperatures as
indicated by G. sacculifer. This resulted in an increase in mixed-layer thickness, pushing
the thermocline to a larger water depth. As N. dutertrei is often characterized as
following the nutrient maximum in the thermocline, it accordingly lived deeper
during glacial stages, and, hence, indicates lower temperatures. Alternatively, it
was suggested that with the closure of the gateway slight upwelling conditions
could have occurred in the Columbia Basin, resulting in colder temperatures in
the thermocline and for N. dutertrei. Obviously in this case it would mean that
upwelling was not very intense as sea surface temperatures meanwhile increased. |
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