Cenozoic Variations in the Deep Western Boundary Current as Recorded in the Seismic Stratigraphy of Contourite Drifts: IODP Expedition 342, Newfoundland Ridge, Offshore Canada

Bathymetric contour parallel currents driven by thermohaline forcings play a significant role in oceanic circulation, deep-sea sedimentation, and the shaping of continental margins. Climatic variability can influence thermohaline forcings and consequently the intensity and path of these currents through time. Mud to fine sand-dominated sedimentary drifts deposited by these currents (contourites) have unique morphological characteristics related to their formation. The J-Anomaly and Newfoundland Ridges, offshore eastern Canada, intersects one of these currents, the Deep Western Boundary Current, providing the necessary conditions for significant and long-lived deposition of contourite drifts. A grid of 56 2-D seismic-reflection profiles combined with nine drill sites from IODP Expedition 342 facilitates the ability to link seismic-scale stratal geometries to a robust chronology and information about sediment character. This integrated dataset affords the ability to map the volumetric sediment distribution of these drifts and hence the dynamics of the Deep Western Boundary Current through phases of abrupt and high-magnitude climate change. Seismic stratigraphic mapping indicates distinct changes in contourite morphologies and depocenters, which are interpreted to reflect changes in current energy and path through time. For example, up-current migrating mud wave-dominated packages are interpreted to represent relatively high-energy environments and occur in younger (post-Oligocene) strata. Shifts in seismic stratigraphic packages from shallower to deeper depths are interpreted to reflect a change in bottom current focus and path. Linking sediment core to seismic stratigraphic interpretations also enables calculation of volumetric sediment accumulation rates, which more accurately describe contourite depositional history than do linear rates obtained from core alone. We also investigate the correlation of our seismic horizons with ocean basin-scale seismic reflectors from previous seismic stratigraphic studies of the North Atlantic. Improved understanding of long-term (10⁵-10⁶yr) dynamics of North Atlantic oceanic circulation in response to significant changes in Cenozoic climate regime provides important context towards refining models and predictions of oceanic response to contemporary climate change.