Re-evaluation of the "elevated epifauna" as indicator of Mediterranean outflow water in the Gulf of Cadiz using stable isotopes (δ13C, δ18O)

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doi: 10.1016/j.gloplacha.2017.06.005
Author(s): García Gallardo, Ángela; Grunert, Patrick; Voelker, Antje H. L.; Mendes, Isabel; Piller, Werner E.
Author Affiliation(s): Primary:
University of Graz, Institute of Earth Sciences, Austria
Other:
Instituto Portugues do Mar e da Atmosfera, Portugal
University of Algarve, Portugal
Volume Title: Global and Planetary Change
Source: Global and Planetary Change, Vol.155, p.78-97. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0921-8181
Note: In English. 140 refs.; illus., incl. 1 plate, 4 tables, sketch map
Summary: The presence and high abundances of the benthic foraminiferal group "elevated epifauna" has been proposed as indicator of the existence of Mediterranean Outflow Water (MOW) in the Gulf of Cadiz. Here we intend to use this potential proxy to reconstruct MOW in the early Pliocene at the Integrated Ocean Drilling Program (IODP) Hole U1387C. Cibicides lobatulus, Planulina ariminensis and Cibicides refulgens were found at this site, but high abundances of C. lobatulus and C. refulgens coincide with increases of shelf taxa and grain size, related to episodes of downslope transport. This issue calls into question the applicability of these species as MOW proxies. The present study therefore reassesses the role of these three elevated epifaunal species by means of stable isotope analyses (δ18O, δ13C) by contrasting their isotopic signature with that of shelf dwellers and deep-water taxa from Pliocene and Recent sediments from the Gulf of Cadiz and the western Iberian margin. Since foraminiferal calcite does not always precipitate in equilibrium with seawater, substantial efforts have been taken in order to determine species-specific offset values and to correct the isotopic signature for vital effects. Our corrected results demonstrate that C. lobatulus and C. refulgens are isotopically similar to the shelf dwellers in the Pliocene data-set, eliminating them as MOW indicators. Recent samples from the Gulf of Cadiz and the western Portugal shelf corroborate the wide bathymetric range of C. lobatulus from the shelf to the slope. Our results thus warrant for caution when considering C. lobatulus and C. refulgens as indicators of bottom current strength in unstable slope settings, particularly when co-occurring with allochthonous shelf dwellers. In contrast, P. ariminensis shows a signature close to deep-water taxa, corroborating its reliability as indicator of MOW.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 07 Marine Geology and Oceanography; Andalusia Spain; Assemblages; Atlantic Ocean; C-13/C-12; Carbon; Cenozoic; Estremadura Promontory; Europe; Expedition 339; Foraminifera; Guadiana River; Gulf of Cadiz; Huelva Spain; Hydrochemistry; IODP Site U1386; Iberian Peninsula; Integrated Ocean Drilling Program; Invertebrata; Isotope ratios; Isotopes; Lis River; Lower Pliocene; Mediterranean Sea; Mediterranean outflow water; Microfossils; Nazare Canyon; Neogene; North Atlantic; Northeast Atlantic; O-18/O-16; Oxygen; Paleo-oceanography; Pliocene; Portugal; Protista; Quaternary; Southern Europe; Spain; Stable isotopes; Tertiary
Coordinates: N364940 N364941 W0074508 W0074508
N363000 N372000 W0071500 W0075500
N385000 N395000 W0091000 W0104500
Record ID: 2017081027
Copyright Information: GeoRef, Copyright 2017 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands