Dominance of Pacific Sourced Deep Water in the Atlantic sector of the Southern Ocean during the last glacials

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<p>The deep Southern Ocean (SO) circulation is of major significance for the understanding of the ocean´s impact on Earth’s climate as uptake and release of CO<sub>­­­2</sub> depend strongly on the redistribution of well and poorly ventilated water masses.</p><p>Neodymium isotopes preserved in deep sea sediment<em> </em>have proven useful to study the deep ocean circulation and water mass provenance thanks to basin scale isotope gradients between the Pacific and the North Atlantic. Here we present novel neodymium isotope data (ε<sub>Nd</sub>) of three sediment cores in 2.8, 3.3 and 3.6 km depth in the Atlantic sector of the SO to assess the presence of old and poorly ventilated Pacific sourced Deep Water (PDW) during the past 150 ka.</p><p>The sediment cores indicate dramatic temporal changes of ε<sub>Nd</sub> spanning a range of 7.7 ε-units from -1.0 to -8.3. While the ε<sub>Nd</sub> variability of the two deeper cores is driven by changes in ocean circulation, the shallowest drilling site is likely influenced by a local source of radiogenic Nd, such as weathering of volcanic material.</p><p>During peak glacial periods with maximum ice extent and a shoaled AMOC we observe radiogenic ε<sub>Nd</sub> values of ~-2.5 to -3.5. This confirms a predominance of glacial PDW at depths of >3 km with proportions close to 100% and thus increasing the water volume portion with enhanced respired carbon. We further advocate for the persistent presence of PDW even during interglacials although with a much smaller proportion.</p><p>Hence, our results enforce the leading role of the SO in storing and reinjecting respired CO<sub>2</sub> into the deep Atlantic Ocean and the Atmosphere during glacial-interglacial terminations.</p>