Glacial reduction of AMOC strength and long term transition in weathering inputs into the Southern Ocean since the Mid Miocene: Evidence from radiogenic Nd and Hf isotopes.

Dausmann, Veit , Frank, Martin , Gutjahr, Marcus and Rickli, Jörg (2017) Glacial reduction of AMOC strength and long term transition in weathering inputs into the Southern Ocean since the Mid Miocene: Evidence from radiogenic Nd and Hf isotopes. Open Access Paleoceanography, 32 (3). pp. 265-283. DOI 10.1002/2016PA003056.

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Abstract

Combined seawater radiogenic hafnium (Hf) and neodymium (Nd) isotope compositions were extracted from bulk sediment leachates and foraminifera of Site 1088, ODP Leg 177, 2082 m water depth on the Agulhas Ridge. The new data provide a continuous reconstruction of long and short-term changes in ocean circulation and continental weathering inputs since the Mid-Miocene. Due to its intermediate water depth the sediments of this core sensitively recorded changes in admixture of North Atlantic Deep Water (NADW) to the Antarctic Circumpolar Current (ACC) as a function of the strength of the Atlantic Meridional Overturning Circulation (AMOC).

Nd isotope compositions (εNd) range from -7 to -11 with glacial values generally 1 to 3 units more radiogenic than during the interglacials of the Quaternary. The data reveal episodes of significantly increased AMOC strength during late Miocene and Pliocene warm periods whereas peak radiogenic εNd values mark a strongly diminished AMOC during the major intensification of Northern Hemisphere Glaciation near 2.8 Ma and in the Pleistocene after 1.5 Ma.

In contrast, the Hf isotope compositions (εHf) show an essentially continuous evolution from highly radiogenic values of up to +11 during the Miocene to less radiogenic present day values (+2 to +4) during the late Quaternary. The data document a long-term transition in dominant weathering inputs, where inputs from the South America are replaced by those from Southern Africa. Moreover, radiogenic peaks provide evidence for the supply of radiogenic Hf originating from Patagonian rocks to the Atlantic sector of the Southern Ocean via dust inputs.

Document Type: Article
Additional Information: WOS:000399449100003
Keywords: AMOC, Southern Ocean, radiogenic isotopes, weathering, overturning circulation
Research affiliation: Kiel University
OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1002/2016PA003056
ISSN: 0883-8305
Projects: ODP
Expeditions/Models/Experiments:
Date Deposited: 13 Mar 2017 10:58
Last Modified: 23 Sep 2019 23:53
URI: http://oceanrep.geomar.de/id/eprint/36921

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