Glacial-interglacial circulation changes inferred from 231Pa/ 230Th sedimentary record in the North Atlantic region

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Glacial-interglacial circulation changes inferred from 231Pa/ 230Th sedimentary record in the North Atlantic region Francois, Roger

Abstract

Studies from the subtropical western and eastern Atlantic Ocean, using the 231Pa/230Th ratio as a kinematic proxy for deep water circulation, provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation (MOC) over the last deglaciation. In this study, we present a compilation of existing and new sedimentary 231Pa/230Th records from North Atlantic cores between 1710 and 4550 m water depth. Comparing sedimentary 231Pa/230Th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the North Atlantic during the last 20,000 years. The 231Pa/230Th ratio measured in upper Holocene sediments indicates slow water renewal above ~2500 m and rapid flushing below, consistent with our understanding of modern circulation. In contrast, during the Last Glacial Maximum (LGM), Glacial North Atlantic Intermediate Water (GNAIW) drove a rapid overturning circulation to a depth of at least ~3000 m depth. Below ~4000 m, water renewal was much slower than today. At the onset of Heinrich event 1, transport by the overturning circulation declined at all depths. GNAIW shoaled above 3000 m and significantly weakened but did not totally shut down. During the Bølling-Allerød (BA) that followed, water renewal rates further decreased above 2000 m but increased below. Our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode, with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the LGM but less accentuated. MOC during the Younger Dryas appears very similar to BA down to 2000 m and slightly slower below. An edited version of this paper was published by AGU. Copyright 2009 American Geophysical Union.

Item Metadata

Title	Glacial-interglacial circulation changes inferred from 231Pa/ 230Th sedimentary record in the North Atlantic region
Creator	Francois, Roger
Contributor	University of British Columbia. Pacific Centre for Isotopic and Geochemical Research
Publisher	American Geophysical Union
Date Issued	2009
Description	Studies from the subtropical western and eastern Atlantic Ocean, using the 231Pa/230Th ratio as a kinematic proxy for deep water circulation, provided compelling evidence for a strong link between climate and the rate of meridional overturning circulation (MOC) over the last deglaciation. In this study, we present a compilation of existing and new sedimentary 231Pa/230Th records from North Atlantic cores between 1710 and 4550 m water depth. Comparing sedimentary 231Pa/230Th from different depths provides new insights into the evolution of the geometry and rate of deep water formation in the North Atlantic during the last 20,000 years. The 231Pa/230Th ratio measured in upper Holocene sediments indicates slow water renewal above ~2500 m and rapid flushing below, consistent with our understanding of modern circulation. In contrast, during the Last Glacial Maximum (LGM), Glacial North Atlantic Intermediate Water (GNAIW) drove a rapid overturning circulation to a depth of at least ~3000 m depth. Below ~4000 m, water renewal was much slower than today. At the onset of Heinrich event 1, transport by the overturning circulation declined at all depths. GNAIW shoaled above 3000 m and significantly weakened but did not totally shut down. During the Bølling-Allerød (BA) that followed, water renewal rates further decreased above 2000 m but increased below. Our results suggest for the first time that ocean circulation during that period was quite distinct from the modern circulation mode, with a comparatively higher renewal rate above 3000 m and a lower renewal rate below in a pattern similar to the LGM but less accentuated. MOC during the Younger Dryas appears very similar to BA down to 2000 m and slightly slower below. An edited version of this paper was published by AGU. Copyright 2009 American Geophysical Union.
Subject	Low-temperature Geochemistry
Genre	Article
Type	Text
Language	eng
Date Available	2017-01-11
Provider	Vancouver : University of British Columbia Library
Rights	Attribution-NonCommercial-NoDerivatives 4.0 International
DOI	10.14288/1.0078394
URI	http://hdl.handle.net/2429/40057
Affiliation	Science, Faculty of; Earth and Ocean Sciences, Department of
Citation	Gherardi, Jeanne Marie; Labeyrie, Laurent D.; Nave, Silvia; Francois, Roger; McManus, Jerry F.; Cortijo, Elsa. 2009. Glacial-interglacial circulation changes inferred from 231Pa/ 230Th sedimentary record in the North Atlantic region. Paleoceanography, 24(2) PA2204.
Publisher DOI	10.1029/2008PA001696
Peer Review Status	Reviewed
Scholarly Level	Faculty
Copyright Holder	Francois, Roger
Rights URI	http://creativecommons.org/licenses/by-nc-nd/4.0/
Aggregated Source Repository	DSpace

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