Technical Note 20/4

LEG 172
NW Atlantic Sediment Drifts

Modified from Proposal 404 Submitted By
L.D. Keigwin, R. Flood, and E.A. Boyle
Staff Scientist: Gary Acton
Co-Chief Scientists: Lloyd D. Keigwin & Domenico Rio
Abstract

The Blake-Bahama Outer Ridge (BBOR) and Carolina Slope are located at the western boundary for deep water circulation in the North Atlantic and the surface waters of the Gulf Stream, which are important as a source of salt and heat to the northern North Atlantic. For this reason, the BBOR is the optimal location to monitor changes in North Atlantic Deep Water (NADW). It is also an excellent location to monitor Antarctic Bottom Water (AABW) because that water mass is recirculated in the subtropics, blending with the exposed NADW. At shallower depths the region is bathed by water from the Labrador Sea, which on geological time scales may be as important a water mass as is the upper NADW. Recently a shallow component to Labrador Sea water has been identified which interacts with the Gulf Stream, probably controlling the distribution of sediment on the Carolina Slope. According to the "Great Ocean Conveyor" paradigm, knowledge of the history of these surface, intermediate, and deep water masses is essential to understanding the world ocean's role in climate change.

Drilling on Leg 172 will provide paleoenvironmental records for late Neogene hemipelagic sediments that are deposited at accelerated rates on western North Atlantic sediment drifts on the BBOR and Carolina Slope. These two areas may represent the only sediment drift locations in the world's oceans where it is possible to conduct high-resolution paleoclimate studies through a 3500-m-range of water depths. Data obtained from the Bermuda Rise site will be compared with data from sites located at deep, high-deposition-rate locations on the BBOR and Carolina Slope to document late Neogene oceanographic changes in the western North Atlantic for millennial as well as Milankovitch times scales over the entire deep and intermediate water column.

To Leg 172 Proposed Site Information