Abstract
Variations in benthic foraminiferal δ13C from a suite of cores located in the equatorial western Atlantic document that the production rate of North Atlantic Deep Water has varied considerably during the last 400,000 years. The cores are located on the eastern slope of Ceara Rise and monitor the chemical variation in deep waters over the depth range of 3200 to 4300 m. Peak production apparently occurred during interglacial stages with isotopic stage 7.3 (216ka) exhibiting the greatest bathymetric extent of NADW. Minima in NAD W bathymetric range occurred during glacial maxima, when significant northward penetration of deep water from the Southern Ocean occupied large portions of the western Atlantic. Minimum production of NADW and maximum penetration of southern-source deep water occurred during glacial stages 4, 8 and 10. During these periods, there is no evidence for NADW at depths below 3200 m.
Climate change and deep water production are linked but the records are complicated because maxima in NADW production do not necessarily occur during the most extreme interglaeials. Also there is a water depth-related difference in the phase relationships between ice volume and deep water production. In the deepest sites, changes in deep water production (as denoted by benthic foraminiferal Δδ13C) appear to lead changes in ice volume (as denoted by benthic foraminiferal δ18O) for both the eccentricity (100 kyr) and obliquity (41 kyr) periods of orbital geometry, providing partial confirmation of the Imbrie et al. (1992) model of a deep water-climate link. But the shallower cores do not lead ice volume at the 100 kyr period. Furthermore, NADW production lags ice volume in the precessional period at all water depths, unlike the records used in the Imbrie et al. (1992) model. Higher frequency, sub-orbital oscillations in benthic foraminiferal 8I3C imply that NADW production is occurring at frequencies like those seen in ice core records. These oscillations in NADW production appear to be restricted to intervals when ice volume was greater than today’s.
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Curry, W.B. (1996). Late Quaternary Deep Circulation in the Western Equatorial Atlantic. In: The South Atlantic. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-80353-6_29
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DOI: https://doi.org/10.1007/978-3-642-80353-6_29
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