LATE QUATERNARY NORTH ATLANTIC PALEOCEANOGRAPHIC RECORDS AND STABLE ISOTOPIC VARIABILITY IN FOUR PLANKTONIC FORAMINIFERAL SPECIES

The distribution of planktonic foraminiferal species in two cores, ENAM 30 and ENAM 94-13, taken within the framework of the European North Atlantic Margin (ENAM) project from water depths of around 1200 m, south-west of the Faeroe Islands, were investigated. The oxygen isotope record of the polar Neogloboquadrina pachyderma sinistral includes Oxygen Isotope Stages (OIS) 4 to OIS 1 in core ENAM 30, whereas that of core ENAM 94-13 precedes the OIS 6/7 boundary. The age of the sediments is based on AMS 14C measurements. The micropaleontological record suggests much more variable hydrographic conditions during OIS 7 to OIS 3, compared to the more stable OIS 2 and OIS 1. Trends of dramatic warming through glacial-interglacial boundaries are followed by a general trend of decreasing temperatures towards the end of interglacial stages. This implies that colder episodes could also develop in the near future of the Holocene at a sub-Milankovitch time scale, after the end of the recent warming phase. The oxygen and carbon isotopic signal of the sub-polar species N. pachyderma dextral, Turborotalita quinqueloba and Globigerina bulloides, from deglacial, interglacial and interstadial sediments, were analyzed for comparison with the signal of N. pachyderma sinistral. Our investigation shows that the low relative abundance of the polar morphotype of N. pachyderma in sediments from warmer climates can yield an isotopic signal that does not correspond to the prevailing climatic conditions of the area at the time slice studied, probably for not being the most representative species of the sample. This fact is further supported by the older AMS 14C age of N. pachyderma, compared to the ages of the sub-polar species from the same level. The signals of the three sub-polar species, on the other hand, show a more coherent trend in the intervals investigated and may reflect better the actual environmental conditions. Warm climatic episodes within Oxygen Isotope Stage 6, indicated by the high relative abundance of sub-polar species, were not apparent in the oxygen isotope record of N. pachyderma sinistral, while the lower values of the isotopic records of the sub-polar species accurately reflect these warmer intervals.