Monitoring fluctuations of the Subtropical Front in the Tasman Sea between 3.45 and 2.45Ma (ODP site 1172).

Ballegeer, Anne-Marie, Flores, José A., Sierro, Francisco J. and Andersen, Nils (2012) Monitoring fluctuations of the Subtropical Front in the Tasman Sea between 3.45 and 2.45Ma (ODP site 1172). PPalaeogeography, Palaeoclimatology, Palaeoecology, 313-314 . pp. 215-224. DOI 10.1016/j.palaeo.2011.11.001.

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Abstract

Calcareous nannoplankton assemblages and benthic δ18O isotopes of Pliocene deep-sea sediments of ODP site 1172 (East of Tasmania) have been studied to improve our knowledge of the Southern Ocean paleoceanography. Our study site is located just north of the Subtropical Front (STF), an ideal setting to monitor migrations of the STF during our study period, between 3.45 and 2.45 Ma.
The assemblage identified at ODP site 1172 has been interpreted as characteristic for the transitional zone water mass, located south of the STF, based on: (i) the low abundances (< 1%) of subtropical taxa, (ii) relatively high percentages of Coccolithus pelagicus, a subpolar type species, (iii) abundances from 2-10% of Calcidiscus leptoporus, a species that frequently inhabits the zone south of the STF and (iv) the high abundances of small Noelaerhabdaceae which at present dominates the zone south of the STF. Across our interval the calcareous nannoplankton manifests glacial-interglacial variability. We have identified cold events, characterized by high abundances of C. pelagicus which coincide with glacial periods, except during G7. After 3.1 Ma cold events are more frequent, in concordance with global cooling trends. Around 2.75 Ma, the interglacial stage G7 is characterized by anomalous low temperatures which most likely are linked to definite closure of the Central American Seaway (CAS), an event that is believed to have had global consequences. A gradual increase of very small Reticulofenestra across our section marks a significant trend in the small Noelaerhabdaceae species group and has been linked to a general enhanced mixing of the water column in agreement with previous studies. It is suggested that a rapid decline of small Gephyrocapsa after isotopic stage G7 might be related to the cooling observed in our study site after the closure of the CAS.
Highlights
► We have analyzed stable isotopes and nannofossils assemblages of the South-Pacific. ► The Subtropical front was situated north of ODP site 1172 between 3.45 and 2.45 Ma. ► The nannofossil assemblages can be divided in a warm and a cold-water assemblage. ► Our results suggest a transition from warm to cold climate conditions after ca. 2.9 Ma.

Document Type: Article
Research affiliation: Kiel University > Kiel Marine Science
OceanRep > The Future Ocean - Cluster of Excellence
Kiel University
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.palaeo.2011.11.001
ISSN: 0031-0182
Projects: Future Ocean
Date Deposited: 27 Mar 2018 10:14
Last Modified: 04 Apr 2019 08:59
URI: http://oceanrep.geomar.de/id/eprint/42422

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