Evolution of Pliocene paleoceanography in the subpolar Atlantic during the onset of Northern Hemisphere Glaciation (NHG) NOW MODIFIED TO: Mid-Pliocene evolution of Mediterranean Outflow Water (MOW) and its salt discharge to the Northeast Atlantic during t

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In the Labrador Sea deep-reaching convection cells presently form Upper North Atlantic Deep Water and govern - together with deepwater sources in the Nordic Seas - the strength of North Atlantic thermohaline circulation (THC) and the related heat transport to northern high latitudes. This convection is highly sensitive to freshwater disturbances induced by meltwater from the Greenland and (glacial) Laurentide ice-sheets and makes this sea a key area to study past climate change. For example, large-amplitude, millennialscale variability in North Atlantic climate in the Pleistocene was intimately linked to ice-sea interaction in the subpolar northwest Atlantic and to changes in Labrador Sea Water formation. Three hypotheses need to be tested to arrive at a better understanding of the role of Labrador Sea paleoceanography during the Late Pliocene onset of Northern Hemisphere Glaciation (NHG) and coeval closure of the Central American Seaway, promoting heat, salt, and moisture transport to northern high latitudes: i) Increased Late Pliocene precipitation in northern Eurasia has led to enhanced freshwater export from the Arctic Ocean to the North Atlantic via the East Greenland Current (EGC) and weakened North Atlantic THC, thus accelerated NHG; ii) Deepwater formation in the Labrador Sea was dominant during less severe Late Pliocene glacials; iii) Millennial-scale climate variability was confined to times of enlarged ice-sheets advancing over northwest Atlantic shelves. We propose to reconstruct the evolution of EGC and LSW at IODP Site U1307 over the onset of NHG (3.3-2.6 Ma) by means of foraminiferal Mg/Ca and stable-isotope records with submillennial time resolution. Precise age control for the well preserved, continuous Late Pliocene sediment section at Site 1307 will also contribute to a Leg-303 Shipboard Party s general objective, that is to generate a chronostratigraphic framework for North Atlantic climate variability.