Paleoclimatic variations in foraminifer assemblages from the Alboran Sea (Western Mediterranean) during the last 150 ka in ODP Site 977

Abstract

Detailed analysis of the planktonic foraminifera assemblages of ODP Site 977, situated in the Alboran Sea (36°1,9′N; 1°57,3′W), led us to recognize 42 planktonic foraminiferal events that occurred during marine isotope stages (MIS) 4 and 5. These events were defined by changes in the abundances of Neogloboquadrina pachyderma (right and left coiling), Turborotalita quinqueloba, Globorotalia scitula, Globorotalia inflata, Globigerina bulloides and Globigerinoides ruber (white and pink varieties). Foraminiferal assemblages changed in response to glacial–interglacial and millennial climate variability throughout the last 150 ka. Based on the estimation of sea surface temperatures (SST) using the modern analog technique and the oxygen isotope data measured in G. bulloides, we inferred the oxygen isotopic composition of sea water (δw). SST increased in the Alboran Sea during the main Dansgaard–Oeschger Interstadials, such as interstadial 19 to 24. Even though N. pachyderma (left coiling) is very scarce before Heinrich Event (HE) 6, three cold pulses can be identified, between 65 and 85 ka ago. Moreover, increases in abundance of T. quinqueloba and G. scitula are recorded during D–O Stadials 20 and 21.

The maximum temperature, which was attained during the Last Interglacial, was about 2 °C higher than recent temperature and that reached over the Holocene. Planktic foraminifera assemblages and paleotemperatures remained cold 3 ka after the beginning of Termination II (T-II), 130 ka ago, probably in connection with the occurrence of Heinrich event 11 in the North Atlantic.

The abundance of G. bulloides during the deposition of organic rich layers (ORLs) of MIS 5, accompanied by lower isotope values in surface waters (δw), could indicate the presence of a fresher surface layer associated with an increase in marine surface productivity.