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Southern Ocean evidence for reduced export of North Atlantic Deep Water during Heinrich event 1

¹Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
²Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, New York 10964, USA

Deep-sea corals form unique, high-resolution archives of ocean circulation that can be dated using the decay of uranium to thorium. They are abundant in the Southern Ocean, and can provide unprecedented insights into ocean circulation and ocean chemistry on sub-millennial time scales in areas where application of traditional paleoceanographic proxies is difficult. Here we present the first coupled neodymium (Nd) isotope and radiocarbon data from deep-sea corals in the Drake Passage (Southern Ocean) adding new constraints on ocean circulation during the last Heinrich event (H1; 16.7 ka). The modern-day Drake Passage water column is homogeneous with respect to Nd isotopes (expressed in epsilon units, _Nd). Its isotopic value of close to –9 is largely controlled by the mixture of North Atlantic Deep Water and Pacific Deep Water. The aragonite of modern Drake Passage corals reflects this water-column value, whereas a fossil coral from H1 is significantly higher at –6.4 ± 0.4. We interpret this ~2.5 unit shift as a reduction in the influence of North Atlantic–sourced Nd in the Southern Ocean during H1. This interpretation is supported by a series of radiocarbon analyses on the same sample, and is consistent with a twofold or greater reduction in export of North Atlantic waters from the Atlantic Basin. Combining analyses of radiocarbon and Nd isotopes on U-series dated deep-sea coral skeletons holds great potential for quantification of past ocean ventilation rates.