Subtropical Northeastern Atlantic intermediate water variability duirng 490-427 ka (late MIS 13 to MIS 12): benthic foraminiferal evidence
High-resolution foraminiferal stable isotopes and benthic foraminiferal faunal records of IODP Site U1391 drilled off the western Iberian margin were adopted to reconstruct intermediate water variability of the subtropical Northeastern Atlantic during the late Marine Isotope Stage (MIS) 13 and MIS 12. Five faunal turnovers were recognized based on multivariate statistical analyses of benthic foraminiferal census data from the size fraction >125 μm. The dominance of Uvigerina peregrina parva and Melonis barleeanum coincides with high benthic foraminiferal accumulation rates (BFAR), high benthic δ13C and the presence of dark-colour sediments during the final stage of MIS 13, also accompanied by frequent occurrences of Planulina ariminensis, an indicator of Mediterranean Outflow Water (MOW), which indicates MOW-related high oxic and mesotrophic to slightly eutrophic bottom water environments. MIS 12c and MIS 12b are characterized by the Bulimina mexicana assemblage, together with low BFAR, high benthic δ13C and the presence of light-colour sediments, revealing oligotrophic and well-oxygenated seafloor conditions associated with the possible advection of nutrient-poor Glacial North Atlantic Intermediate Water (GNAIW) to the studied site. A prominent increase in organic matter supply and a slight decrease in dissolved oxygen concentration during MIS 12a were reflected by more abundant Bulimina aculeata, higher BFAR, lower benthic δ13C and the darker-colour sediments relative to MIS 12c-b. A shift in the dominant species and significantly decreased benthic δ13C, suggest an increased influence of southern-sourced waters (SSW) and a decreased influence of GNAIW during MIS 12a. At the beginning of Termination V (TV), infaunal taxa mainly composed of B. aculeata, Bulimina exilis, Nonionella turgida, Brizalina sp. and Uvigerina proboscidea dominate the benthic foraminiferal population, which may be attributed to eutrophic and poorly-oxygenated bottom water environment strongly influenced by SSW. Afterwards, N. turgida rapidly became the predominant taxa, and its predominance was probably the result of further reduction in dissolved oxygen concentration.