Response of the pelagic environment to palaeoclimatic changes in the central Mediterranean Sea during the Late Quaternary

Three central Mediterranean deep-sea cores have been studied to reconstruct the palaeoclimatic history of the basin over the time interval 34-0 kyr BP. The intensity and duration of the climatic events that occurred in the Mediterranean Sea during the last glacial-postglacial transition were estimated by observing compositional changes in the planktonic foraminifera and calcareous nannoplankton (coccolithophores) assemblages, together with a reconstruction of sea surface temperatures (using Modern Analogue Technique and U-37(k') index), the delta O-18 signal and pteropod fluxes. The application of two independent and well established techniques for the determination of the past SST led to a number of considerations about the accuracy and efficacy of the use of such methodologies in the Mediterranean Sea, notoriously dominated by local factors and characterised by a number of independent environments. The recognition of millennial to centennial climatic instabilities, in both the SST and microfossil records, was possible because of the high resolution of the study. A succession of nine main biozones and six subzones, based on the major changes in the planktonic foraminifera records, has been recognised and compared with GRIP and GISP2 ice cores delta O-18 values and with records from four other studies from the central Mediterranean Sea. During the early phase of the Holocene, a period characterised by relatively higher temperatures and lighter delta O-18 values has been recognised as being coeval with the 'Climatic Optimum' (between 10.5 and 6.1 kyr BP, calendar age). This interval was characterised by an abrupt drop in the pteropods relative abundances and fluxes. The pteropodal fossil assemblage may have been affected by a possible event of selective dissolution of the aragonite driven by the shoaling of the ACD. A coeval change in the position of the pycnocline may have been responsible for a strong relative increase in abundance of Neogloboquadrina pachyderma r.c., and a decrease in the abundance of Globorotalia inflata in the western sector of the Mediterranean Sea. (C) 2001 Elsevier Science B.V. All rights reserved.