Glacial-to-deglacial changes in North Atlantic meltwater advection and deep-water formation – Centennial-to-millennial-scale 14 C records from the Azores plateau

• Published in: Geochimica et Cosmochimica Acta
• Main Authors: Balmer, Sven, Sarnthein, Michael
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2018
• Subjects: Iceland; Labrador Sea; NADW; North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/43927/; https://oceanrep.geomar.de/id/eprint/43927/1/Balmer.pdf; https://doi.org/10.1016/j.gca.2018.03.001

The last deglacial was marked by tremendous changes in ocean temperature and circulation as well as atmospheric CO2 and 14C. We employed the “14C plateau-tuning technique” to a centennial-scale planktic 14C record of core MD08-3180 retrieved S.W. of the Azores Islands at ∼3060 m water depth to establish both a new standard of absolute age control and a record of past 14C reservoir ages of ocean surface waters. Both δ18O minima of G. bulloides and high planktic reservoir ages of ∼1600 to 2170 yr suggest two major melt water incursions that reached from the Labrador Sea up to the subtropics over Heinrich Stadial 1 (HS-1). In parallel, we established a record of (apparent) benthic ventilation ages that add the planktic 14C reservoir ages together with the benthic-planktic 14C age difference at the site and time of deposition, a sum finally adjusted to past changes in atmospheric 14C that occurred since the time of deep-water formation. Near the Azores apparent deep-water ages of the Last Glacial Maximum were as low as 340–740 yr, which suggests a lateral advection of young North Atlantic Deep Waters (NADW) from subpolar regions south of Iceland, in harmony with recent model simulation and in contrast to a widely assumed major shoaling of glacial deep-water formation. During HS-1, local benthic ventilation ages increased up to 2200–2550 yr, thus suggest an incursion of old southern-source deep waters, an unstable regime that was interrupted by brief pulses of NADW incursion near 16, 15.6 cal. ka, and most salient, near 14.9/14.7 ka.