Subtropical Northeastern Atlantic intermediate water variability duirng 490-427 ka (late MIS 13 to MIS 12): benthic foraminiferal evidence
Description
High-resolution foraminiferal stable isotopes and benthic foraminiferal faunal records of IODP Site U1391 were adopted to reconstruct the subtropical Northeastern Atlantic intermediate water variability from the late Marine Isotope Stage (MIS) 13 to MIS 12. Five faunal turnovers were recognized based on multivariate statistical analyses of benthic foraminiferal census data from the size fraction >250 μm. The dominance of Uvigerina peregrina parva 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 miliolids - 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 the dominance of Bulimina aculeata and miliolids, high BFAR, low benthic δ13C and the dark-colour sediments. A shift in foraminiferal composition from the dominance of miliolids and Bulimina mexicana to the dominance of Bulimina aculeata and miliolids, combined with significantly decreased benthic δ13C, suggests an increased influence of southern-sourced waters (SSW) and a decreased influence of GNAIW. At the beginning of Termination V (TV), infaunal taxa mainly composed of Uvigerina proboscidea, B. aculeata and Globobulimina pacifica dominate the benthic foraminiferal population, which may be attributed to eutrophic and poorly-oxygenated bottom water environment strongly influenced by SSW. Afterwards, miliolids rapidly became the predominant taxa. The predominance of miliolids was probably the result of selective carbonate dissolution caused by the corrosiveness of pore water related to decomposition of organic matter.