12:15 PM - 12:30 PM
[MIS34-10] Abrupt intensification of North Atlantic Deep Water formation at the Nordic Seas during the late Pliocene transition
Here, we developed a new rock-magnetic method to determine constituent of sediments and report on the evolution of NADW during LPT. North Atlantic deep-sea sediments drilled at the Gardar Drift (Integrated Ocean Drilling Program site U1314) were used for rock-magnetic measurements. We measured isothermal remanence (IRM) acquisition curves of 252 samples collected from 199.3 to 299.2 mcd of the core, which correspond to ages between 2.22 and 2.91 Ma at an average resolution of 3 kyr.
First derivatives of the IRM curves were decomposed into two end-member components. Consequently, residuals of the decomposition were sufficiently small throughout the study interval, thus confirming that the Gardar Drift sediments represent a mixing of the two end-member components: high-coercivity and low-coercivity components. Changes in the components agree well with those of the LR04 oxygen isotope data of benthic foraminifera [Lisiecki and Raymo, 2005]; the fraction of high-coercivity component periodically changed with the interglacial?glacial cycle. Variation trends of the sediment constituents drastically changed at ca. 2.68 Ma. Average values of the fraction of high-coercivity component increased after ca. 2.68 Ma from 38 ± 13% to 68 ± 22% because of the increase in high-coercivity component during the interglacial period.
Fraction changes of the high-coercivity component represent variation of the Iceland-Scotland Overflow Water, a branch of NADW formed at the Nordic Seas. The drastic increase in the high-coercivity component during the interglacial period suggests that intense NADW formation at the Nordic Seas abruptly started at ca. 2.68 Ma.