Planktonic foraminiferal variations in the southwestern Atlantic since the last glacial-interglacial cycle

Abstract

Relative abundances of planktonic foraminiferal species from two cores from the subtropical, southwestern Atlantic indicate changes in oceanic conditions during the last glacial-interglacial cycle. During interglacial intervals (biozone X or Marine Isotopic Stage 5 (MIS-5) and biozone Z or MIS-1), the relative abundance of the intermediate water-dwelling species of menardiform plexus was high, whereas those of deep-dwelling species Globorotalia truncatulinoides and Globorotalia inflata were relatively low, suggesting high temperature conditions (≥22°C) and/or increased upper-water stratification during this period of time. In contrast, the absence of menardiform plexus and high abundances of cold-water species (G. truncatulinoides and G. inflata) during the glacial interval (biozone Y [MIS-4, MIS-3, and MIS-2]) suggest cold-water conditions (≤22°C) and/or a reduction of upper-water stratification. Two intervals of moderate temperature and/or low salinity during the last glaciation, however, are suggested by the increase in abundance of Pulleniatina plexus. Foraminiferal fauna have suggested a difference of 1 to 2°C between the last glacial interval and the late Holocene. Millennial-scale paleoceanographic events have been identified during the last interglacial interval (MIS-5), suggesting that warm conditions and/or a stratified water column were replaced by short intervals of cooler water and reduced upper-water stratification, as indicated by changes in abundances of menardiform plexus and G. truncatulinoides. The short interval during which menardiform plexus disappeared during the Holocene suggests a temperature decrease and can be related to the widespread stadial event in the Holocene at 8.2 ka. Copyright © 2014, SEPM (Society for Sedimentary Geology).