46. CLIMATICALLY INDUCED CHANGES IN VERTICAL WATER MASS STRUCTURE OF THE VEMA CHANNEL DURING THE PLIOCENE: EVIDENCE FROM DEEP SEA

• Main Authors: David A. Hodell, James P. Kennett, Graduate School Of Oceanography
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Arctic; Foraminifera*; NADW; North Atlantic Deep Water; North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.530.205; http://www.deepseadrilling.org/72/volume/dsdp72_46.pdf

Pliocene changes in the vertical water mass structure of the western South Atlantic are inferred from changes in ben-thic foraminiferal assemblages and stable isotopes from DSDP Holes 516A, 517, and 518. Factor analysis of 34 samples from Site 518 reveals three distinct benthic foraminiferal assemblages that have been associated with specific subsurface water masses in the modern ocean. These include a Nuttalides umbonifera assemblage (Factor 1) associated with Ant-arctic Bottom Water (AABW), a Globocassidulina subglobosa-Uvigerina peregrina assemblage (Factor 2) associated with Circumpolar Deep Water (CPDW), and an Oridorsalis umbonatus-Epistominella exigua assemblage associated with North Atlantic Deep Water (NADW). Bathymetric gradients in Δ13C between Holes 516A (1313 m), 517 (2963 m), and 518 (3944 m) are calculated whenever possible to monitor the degree of similarity and/or difference in the apparent oxygen utilization (AOU) of water masses located at these depths during the Pliocene. Changes in bathymetric Δ13C gradients coupled with benthic foraminiferal assemblages record fundamental changes in the vertical water mass struc-ture of the Vema Channel during the Pliocene from 4.1 to 2.7 Ma. At Site 518, the interval from 4.1 to 3.6 Ma is dominated by the N. umbonifera (Factor 1) and O. umbonatus-E. ex-igua (Factor 3) assemblages. The Δ13C gradient between Holes 518 (3944 m) and 516A (1313 m) undergoes rapid oscilla-tions during this interval though no permanent increase in the gradient is observed. However, δ13C values at Site 518 are