Planktonic Foraminifera as Sensitive Recorders of Climate Variability in the Eastern Mediterranean During the Last ~90 ka
Wednesday, 17 December 2014
Planktonic foraminifera (PF) are widely used in Quaternary paleoceanography as carriers of oxygen stable isotope signal. This signal is one of the main tools for establishing chronostratigraphy and determining the nature of global and local glacial and interglacial cycles. In this study, the focus is on the PF assemblages which are sensitive recorders of climate and water column properties including the degree of water column stratification and trophic levels. In order to reconstruct the climate variability of the last ~90 ka, core MDVAL9501 (980 m water depth), taken by R/V Marion Dufresnae, SE of Cyprus, was studied. A δ18O-Globigerinoides ruber stratigraphy was established and correlated with well-dated (U/Th) speleothem records of Soreq Cave and radiocarbon dates. The sedimentary record in this core covers the last ~90ka. Variations in PF assemblage composition indicate that conditions shifted between two main climatic scenarios. During the last glacial cooler, more aerated, less stratified and more mesotrophic water column persisted with distinct seasonality. This is evident from the occurrence of two deep water dwellers Globorotalia inflata being abundant from 75 to 50 ka BP and G. scitula from 55 to 15 ka BP (with respective SST of 15-16 ºC and 11-13 ºC) and accompanied continuously by the cold water species Neogloboqudrina pachyderma and Globigerina bulloides. Among the "warm" water species G. ruber is nearly the only "survivor" during the glacial period comprising 25-50% of the assemblage with lower values corresponding to minima in D-O events. During Holocene, water column was warmer, more stratified, mostly oligotrophic with reduced seasonality. The dominating species were G. ruber and other "warm” water species comprising >75% of the assemblage and occurring in low numbers. An exception are sapropel S1 (early Holocene) and S3 (MIS 5.1) periods, when lower δ18O and highest TOC values prevail with significantly increased numerical abundance of PF, indicating a temporary change to more mesotrophic water-column conditions.