Dynamic intermediate ocean circulation in the North Atlantic during Heinrich Stadial 1:A radiocarbon and neodymium isotope perspective

• Published in: Paleoceanography
• Main Authors: Wilson, David J., Crocket, Kirsty C., van de Flierdt, Tina, Robinson, Laura F., Adkins, Jess F.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2014
• Subjects: Heinrich stadial; deglaciation; Atlantic meridional overturning circulation; neodymium isotopes; radiocarbon; deep sea corals; Greenland; Iceland; North Atlantic
• Online Access: https://pure.uhi.ac.uk/en/publications/21a000fd-eeeb-4417-9170-ed31190be071; https://doi.org/10.1002/2014PA002674; https://pureadmin.uhi.ac.uk/ws/files/1810611/Wilson_et_al_Paleoceanog_2014_14C_and_eNd_perspective_on_NWAtl_circulation.pdf; http://onlinelibrary.wiley.com/doi/10.1002/2014PA002674/abstract

The last deglaciation was characterized by a series of millennial-scale climate events that have been linked to deep ocean variability. While often implied in interpretations, few direct constraints exist on circulation changes at mid-depths. Here we provide new constraints on the variability of deglacial mid-depth circulation using combined radiocarbon and neodymium isotopes in 24 North Atlantic deep-sea corals. Their aragonite skeletons have been dated by uranium-series, providing absolute ages and the resolution to record centennial-scale changes, while transects spanning the lifetime of a single coral allow subcentennial tracer reconstruction. Our results reveal that rapid fluctuations of water mass sourcing and radiocarbon affected the mid-depth water column (1.7–2.5 km) on timescales of less than 100 years during the latter half of Heinrich Stadial 1. The neodymium isotopic variability (−14.5 to −11.0) ranges from the composition of the modern northern-sourced waters towards more radiogenic compositions, suggesting the presence of a greater southern-sourced component at some times. However, in detail, simple two-component mixing between well-ventilated northern-sourced and radiocarbon-depleted southern-sourced water masses cannot explain all our data. Instead, corals from ~15.0 ka and ~15.8 ka may record variability between southern-sourced intermediate waters and radiocarbon-depleted northern-sourced waters, unless there was a major shift in the neodymium isotopic composition of the northern end-member. In order to explain the rapid shift towards the most depleted radiocarbon values at ~15.4 ka, we suggest a different mixing scenario involving either radiocarbon-depleted deep water from the Greenland-Iceland-Norwegian Seas or a southern-sourced deep water mass. Since these mid-depth changes preceded the Bolling-Allerod warming and were apparently unaccompanied by changes in the deep Atlantic, they may indicate an important role for the intermediate ocean in the early deglacial climate evolution.