Central North Atlantic (IODP Site U1313) paleoceanography based on a high-resolution dinoflagellate cyst record across the Early–Middle Pleistocene boundary (Marine Isotope Stages 20–18, ~810–741 ka)
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A dinoflagellate cyst (dinocyst) study of 102 samples from Integrated Ocean Drilling Program Site U1313 in the central North Atlantic Ocean represents the most detailed dinocyst record yet available for Marine Isotope Stage (MIS) 19, which spans the Lower–Middle Pleistocene boundary. A published ultra-high-resolution δ18O record constrains the study. The following paleoenvironmental indicators were among those used: Operculodinium centrocarpum sensu Wall & Dale (North Atlantic Current [NAC]), Nematosphaeropsis labyrinthus (sub-polar water masses), total Impagidinium spp. (subtropical gyre), and total protoperidiniacean cysts and total cyst concentrations (productivity indicators). Cooling just prior to Termination IX suggests a Younger-Dryas type event. An early arrival of the North Atlantic Current at ~797 ka and then warm subtropical gyre waters at 793.58 ka, presage the arrival of oligotrophic waters at 790.5 ka. The onset of peak interglacial conditions at 790.5 ka is delayed relative to the benthic δ18O signal, which has a midpoint age for Termination IX at ~793 ka, and presumably reflects the persistence of ice sheets to the north. Peak interglacial conditions terminated at 784 ka with a duration of ~6500 years. This is shorter than the 10.5–12.5 kyr extent of full interglacial conditions recorded elsewhere and based on different criteria. Dinocyst transfer functions give August sea-surface temperatures of ~20°C for peak interglacial conditions, a few degrees cooler than at present. Subpolar water masses occupied Site U1313 in late MIS 19, but at 750.89 ka (early MIS 18) a return of the North Atlantic Current was followed by further warming, with an August sea-surface temperature of 20 °C for the highest sample at 741.41 ka.