Paleoceanography of marine isotope stage 31 in the northwest North Atlantic

English Abstract:

We investigated paleoceanographic conditions during Marine Isotope Stage (MIS) 31 at IODP site 1305, off southwest Greenland in the Labrador Sea, based on the analysis of dinocyst and foraminiferal assemblages, in addition to isotopic measurements in planktic foraminifers as complementary tracers of properties in mesopelagic and epipelagic water masses. The Modern Analogue Technique (MAT) has been applied to reconstruct sea surface conditions using dinocyst assemblages. Low salinity conditions (32-34.5), large seasonal temperature gradients with cool winters (3-6°C) and mild summer (10-15°C) characterized the surface water mass. In contradistinction, the application of MAT to foraminifers assemblages, which are largely dominated by the deep dwelling species Neogloboquadrina pachyderma left coiling, indicate very cold conditions both in winter (-2-0°C) and summer (2-4°C), a range consistent with the observed isotopic composition of planktic foraminifers. Hence, the discrepancy between dinocyst vs planktic foraminifer reconstructions suggests strongly stratified, relatively warm surface waters, overlying a cold and more saline intermediate water mass. These results lead to infer conditions unfavorable for convection and intermediate- or deep-water formation in the Labrador Sea during the interval.