CENTRAL NORTH ATLANTIC (IODP SITE U1313) PALEOCEANOGRAPHY AND THE STRUCTURE OF MARINE ISOTOPE STAGE 21 (EARLY PLEISTOCENE, 866–814 KA) BASED ON A HIGH-RESOLUTION DINOFLAGELLATE CYST RECORD

A high-resolution dinoflagellate cyst record coupled with other available data for Integrated Ocean Drilling Program (IODP) Site U1313 has been acquired to enhance understanding of the paleoceanography and structure of Marine Isotope Stage (MIS) 21 in the central North Atlantic. MIS 21 occurs within the Early–Middle Pleistocene transition and is well known to be climatically unstable, with seven substages recognized for this interglacial. No significant orbital forcing can explain this structure, which implies that changes internal to the climate system are responsible. Site U1313 is situated near the northern margin of the North Atlantic subtropical gyre, and is therefore a sensitive recorder of the position of the nutrient-elevated North Atlantic Current (NAC). During glacial intervals, the NAC shifts southwards where it influences Site U1313, whereas during interglacials the NAC returns north of Site U1313, which is then bathed in the oligotrophic waters of the Subtropical Gyre. A previously published high resolution oxygen isotope study of the foraminifera of MIS 21 at Site U1313 (Ferretti et al., 2010, Earth and Planetary Science Letters, 293: 28–41) has revealed the structure of this interglacial and its bounding glacials in unprecedented detail. The present investigation of the dinoflagellate cysts uses sediment saved from the Ferretti et al. study after sieving for foraminifera. Results can therefore be related directly to the isotopic trends. A total of 94 samples were processed that all yielded dinoflagellate cysts. A total of 26 species has been recorded, of which the following are commonly found in most samples: Impagidinium spp., Pyxidinopsis reticulata, Nematosphaeropsis labyrinthus, cysts of Protoceratium reticulatum, Bitectatodinium tepikiense, Pyxidinopsis sp., Brigantedinium cariacoense, and Brigantedinium simplex. Species of the mostly oligotrophic genus Impagidinium typically dominate assemblages. specimens are well preserved and considered in-situ. Preliminary findings suggest that fluctuations in assemblage composition throughout the interval result from nutrient fluxes reflecting perturbations in the NAC during MIS 21