Neodymium isotopic evidence for linked changes in Southeast Atlantic and Southwest Pacific circulation over the last 200 kyr

Hu, Rong and Noble, Taryn L. and Piotrowski, Alexander M. and McCave, I. Nicholas and Bostock, Helen C. and Neil, Helen L. (2016) Neodymium isotopic evidence for linked changes in Southeast Atlantic and Southwest Pacific circulation over the last 200 kyr. Earth and Planetary Science Letters, 455. pp. 106-114. ISSN 0012-821X DOI 10.1016/j.epsl.2016.09.027

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Official URL: http://doi.org/10.1016/j.epsl.2016.09.027

Abstract

Knowledge of the geometry and strength of the deep overturning circulation is central to the understanding of past climate variability on glacial–interglacial (G–I) timescales. In this study, neodymium (Nd) isotopic ratios on planktonic foraminifera are used to reconstruct the water mass source and mixing history of intermediate and deep water in the Southeast (SE) Atlantic and Southwest (SW) Pacific over the past 200 kyr from five sediment cores. Nd isotopes from a depth transect of cores in the SE Atlantic displayed a stronger geochemical gradient around 3.5 km at the LGM, with higher εNd values of ∼−6.0 below that boundary than those of ∼−7.8 above. In contrast, a similar εNd value (∼−9.5) is observed at both the intermediate and abyssal depths in the Holocene. The glacial upper ocean is 1.8 εNd units less radiogenic than the lower ocean, reflecting an increase in the amount of North Atlantic Component Water (NACW) in the upper SE Atlantic. A coherent Nd isotope change was observed in the SE Atlantic and SW Pacific intermediate and deep water with major excursion to more radiogenic εNd values during Marine Isotope Stage (MIS) 2, 4 and 6. This suggests the flux of NACW to the Southern Ocean was reduced during cold marine stages, possibly accompanied by changes in the water mass geometry. The constant 2 εNd-unit offset between intermediate water in the SE Atlantic and SW Pacific suggests the persistent propagation of less radiogenic NACW to the upper Pacific Ocean over the last glacial cycle. Moreover, the larger glacial vertical εNd gradients between the intermediate and deep waters in both the SE Atlantic and SW Pacific indicate a decreased proportion of NACW entrainment into the deep oceans, consistent with studies proposing reduced mixing between the upper and lower meridional overturning cells.

Item Type: Article
Uncontrolled Keywords: 2016AREP; IA72;
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Earth and Planetary Science Letters
Volume: 455
Page Range: pp. 106-114
Identification Number: 10.1016/j.epsl.2016.09.027
Depositing User: Sarah Humbert
Date Deposited: 24 Feb 2017 14:15
Last Modified: 02 Mar 2017 20:55
URI: http://eprints.esc.cam.ac.uk/id/eprint/3830

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