Hohbein, Michael W.; Sexton, Philip F. and Cartwright, Joseph A.
Onset of North Atlantic Deep Water production coincident with inception of the Cenozoic global cooling trend.
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Here we show that the onset of deep water overflow from the Norwegian-Greenland Sea into the North Atlantic, interpreted to represent the onset of a modern-style North Atlantic Deep Water mass, commenced close to the early to middle Eocene boundary. This finding is based on the identification of a large, elongate contourite sediment drift, the “Judd Falls Drift,” in the Faeroe-Shetland Basin, through detailed mapping of high-resolution two-dimensional and three-dimensional seismic data. This sediment drift covers an area of ∼9000 km2 in one of the critical present-day deep water gateways into the North Atlantic Ocean. Interpretation of the body as a contourite drift is based on standard seismic-stratigraphic diagnostic criteria including tridirectional onlap, lensoid sediment geometry, upslope progradational configurations of stacked onlap units, and an erosional base cut in a deepwater setting. The internal reflection configuration indicates that the drift was deposited under a southwest-flowing current regime, which we propose represents the onset of North Atlantic Deep Water production, with continual deep water flow until at least the latest Eocene (ca. 35 million years ago [Ma]). Onset of drift deposition is dated by several key boreholes as occurring at ca. 50–49 Ma, across the early to middle Eocene boundary, and is coincident with independent geochemical evidence for major changes in the configuration of deep-sea circulation patterns, global biological production, and the onset of Cenozoic climatic cooling. These temporal concurrences suggest a strong link between the initiation of North Atlantic Deep Water production and Cenozoic global climate evolution.
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