Bottom ocean currents revealed by Anisotropy of Magnetic Susceptibility in the North Atlantic Ocean: Data from IODP Expeditions 384, 395C and 395

Abstract

We report preliminary results from the magnetic stratigraphy and the anisotropy of magnetic susceptibility (AMS) of 6 sites drilled from the International Ocean Discovery Program Expeditions 384, 395C and 395 in the North Atlantic Ocean. Five sites were drilled along a transect on the eastern side of the modern Reykjanes Ridge (including Gardar drift and Bjorn drift), and one on its western side, close to Greenland (Eirik drift). The magnetic stratigraphy provides a precise record of geomagnetic reversals that, coupled with biostratigraphic data, was used to build an age model for each site. The resulting age models provide constraints on variations in sedimentation rate, as well as variations in the AMS parameters. The AMS was used to investigate the strength and direction of bottom currents, with implications for oceanic gateway evolution. The AMS data were reoriented using the shipboard mean declination of the cores at 20 mT, assuming a geocentric axial dipole hypothesis, and time-averaged paleosecular variation. The AMS parameters (lineation, foliation, anisotropy factor, and shape parameter) document the onset and change in the strength of bottom currents. The current direction is generally consistent with that of modern instrumental measurements (NNE - SSW), at least in the last 2.5 Myr.