Reconstructing initial mediterranean outflow from benthic Foraminifera

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Author(s): Garcia Gallardo, Angela; Grunert, Patrick; Voelker, Antje H. L.; Mendes, Isabel; Piller, Werner E.
Author Affiliation(s): Primary:
University of Graz, Institute for Earth Sciences, Graz, Austria
Instituto Portugues do Mar e da Atmosfera, Portugal
University of the Algarve, Portugal
Volume Title: AGU 2016 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2016; American Geophysical Union 2016 fall meeting, San Francisco, CA, Dec. 12-16, 2016. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: The onset of Mediterranean Outflow Water (MOW) takes place after the opening of the Gibraltar Strait (5.33 Ma). Its impact on oceanography and climate in the present is widely studied but its role in the early Pliocene is not well explored yet. Quantitative analysis of benthic foraminifera has been performed on sediment samples from the lower part of IODP Hole U1387C (IODP Expedition 339) in order to reconstruct paleoenvironmental changes during the late Miocene-early Pliocene. Micropaleontological records reveal a shift from reduced oxygenation in the late Miocene to a better ventilated setting during the early Pliocene likely related to the first evidence of Mediterranean-Atlantic exchange. Increased abundances of the functional benthic foraminiferal "elevated epifauna" group have been directly related to MOW in the Gulf of Cadiz since they are adapted to settle on substrates above the sediment surface to catch food particles from strong bottom currents (Schonfeld, 2002). In our study, the elevated epifauna is represented by Planulina ariminensis, Cibicides lobatulus and C. refulgens. However, our early Pliocene records reveal that peak abundances of C. lobatulus and C. refulgens are well correlated with allochthonous shelf taxa and grain-size maxima, suggesting downslope transport to deeper settings. To clarify this issue, stable isotope analyses (δ18O, δ13C) have been performed on shells of shelf dwellers, deep water taxa and elevated epifauna from Pliocene and present-day samples from the Iberian Margin. Preliminary results indicate that some elevated epifaunal elements have a broad bathymetric range and are not always autochthonous to deeper settings. In the early Pliocene Gulf of Cadiz, characterized by frequent turbidite deposition, P. ariminensis would thus remain the only reliable indicator of MOW. Schonfeld, J., 2002. A new benthic foraminiferal proxy for near-bottom current velocities in the Gulf of cadiz, Northeastern Atlantic Ocean. Deep-Sea Res I 49:1853-1875.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Atlantic Ocean; Expedition 339; Foraminifera; Gulf of Cadiz; IODP Site U1387; Integrated Ocean Drilling Program; Mediterranean region; Microfossils; North Atlantic
Coordinates: N364819 N364820 W0074308 W0074308
Record ID: 2018008296
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