Elsevier

Earth and Planetary Science Letters

Volume 484, 15 February 2018, Pages 329-340
Earth and Planetary Science Letters

Astronomically paced changes in deep-water circulation in the western North Atlantic during the middle Eocene

https://doi.org/10.1016/j.epsl.2017.12.016Get rights and content
Under a Creative Commons license
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Highlights

  • First high-resolution (<2 kyr/sample) mid-Eocene benthic foraminiferal isotope record.

  • Middle Eocene NCW intensity is primarily paced by obliquity.

  • Obliquity minima are associated with strong NCW and DWBC.

  • GNS surface cooling drives deep-water formation during obliquity minima.

Abstract

North Atlantic Deep Water (NADW) currently redistributes heat and salt between Earth's ocean basins, and plays a vital role in the ocean-atmosphere CO2 exchange. Despite its crucial role in today's climate system, vigorous debate remains as to when deep-water formation in the North Atlantic started. Here, we present datasets from carbonate-rich middle Eocene sediments from the Newfoundland Ridge, revealing a unique archive of paleoceanographic change from the progressively cooling climate of the middle Eocene. Well-defined lithologic alternations between calcareous ooze and clay-rich intervals occur at the ∼41-kyr beat of axial obliquity. Hence, we identify obliquity as the driver of middle Eocene (43.5–46 Ma) Northern Component Water (NCW, the predecessor of modern NADW) variability. High-resolution benthic foraminiferal δ18O and δ13C suggest that obliquity minima correspond to cold, nutrient-depleted, western North Atlantic deep waters. We thus link stronger NCW formation with obliquity minima. In contrast, during obliquity maxima, Deep Western Boundary Currents were weaker and warmer, while abyssal nutrients were more abundant. These aspects reflect a more sluggish NCW formation. This obliquity-paced paleoceanographic regime is in excellent agreement with results from an Earth system model, in which obliquity minima configurations enhance NCW formation.

Keywords

NADW
AMOC
astronomical forcing
middle Eocene
IODP

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