Pleistocene ice-rafted debris events recorded at the Agulhas Plateau - indicators of intermittent Indian-Atlantic gateway closure
Interocean exchange of heat and salt around South Africa - the so called 'Agulhas Leakage' - is thought to be a key link in the maintenance of the Atlantic meridional overturning circulation (AMOC). It takes place at the Agulhas Retroflection, largely by the intermittent shedding of enormo...
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ftunivutrecht:oai:dspace.library.uu.nl:1874/396233 2023-07-23T04:20:47+02:00 Pleistocene ice-rafted debris events recorded at the Agulhas Plateau - indicators of intermittent Indian-Atlantic gateway closure Ziegler, M. Hall, I. R. Siret, P. J. Zahn, R. non-UU output of UU-AW members 2012-04-01 image/pdf https://dspace.library.uu.nl/handle/1874/396233 en eng 1029-7006 https://dspace.library.uu.nl/handle/1874/396233 info:eu-repo/semantics/OpenAccess Abstract 2012 ftunivutrecht 2023-07-02T03:08:58Z Interocean exchange of heat and salt around South Africa - the so called 'Agulhas Leakage' - is thought to be a key link in the maintenance of the Atlantic meridional overturning circulation (AMOC). It takes place at the Agulhas Retroflection, largely by the intermittent shedding of enormous rings that penetrate into the South Atlantic Ocean (Lutjeharms, 1996, Biastoch et al., 2008; Beal et al., 2011). Recent palaeoceanographic studies suggest that variability in the latitudinal position of the subtropical front (STF) in the Southern Ocean, act as a gatekeeper for the Agulhas retroflection and moreover, that a variable northward migration of the STF potentially modulated the severity of glacial periods by altering the amount of Agulhas leakage with consequences for the AMOC (Bard and Rickaby, 2009). Here we present a high-resolution record of ice rafted debris (IRD) from the southern Agulhas Plateau (sediment core MD02-2588, 41°19,90 S and 25°49,70 E, 2907 m water depth) covering the last 350,000 years. We find distinct millennial scale events with high abundances of IRD in the sediments. Scanning-electron microscope analysis of individual grains shows a wide range of morphologies, with a high degree of angularity being a dominant feature, with surface microfeatures (linear fractures, grooves and troughs) that are typical for glacial origin and transport. We interpret these IRD events as indicators for a northward shift of the Southern Ocean frontal system, thereby allowing sufficient cooling and iceberg survivability as far north as the Agulhas Plateau. Our proxy record suggests significant millennial scale variability of the frontal movements throughout the last three glacial cycles. Largest IRD peaks occur during marine isotope stage 8 (~300 ka BP) and hence during a period for which an extreme northward shift in the STF has been identified previously (Bard and Rickaby, 2009). We compare our IRD record with records of millennial scale climate variability in the North Atlantic (McManus et al., 1999, Martrat et ... Article in Journal/Newspaper North Atlantic South Atlantic Ocean Southern Ocean Utrecht University Repository Indian Southern Ocean |
institution |
Open Polar |
collection |
Utrecht University Repository |
op_collection_id |
ftunivutrecht |
language |
English |
description |
Interocean exchange of heat and salt around South Africa - the so called 'Agulhas Leakage' - is thought to be a key link in the maintenance of the Atlantic meridional overturning circulation (AMOC). It takes place at the Agulhas Retroflection, largely by the intermittent shedding of enormous rings that penetrate into the South Atlantic Ocean (Lutjeharms, 1996, Biastoch et al., 2008; Beal et al., 2011). Recent palaeoceanographic studies suggest that variability in the latitudinal position of the subtropical front (STF) in the Southern Ocean, act as a gatekeeper for the Agulhas retroflection and moreover, that a variable northward migration of the STF potentially modulated the severity of glacial periods by altering the amount of Agulhas leakage with consequences for the AMOC (Bard and Rickaby, 2009). Here we present a high-resolution record of ice rafted debris (IRD) from the southern Agulhas Plateau (sediment core MD02-2588, 41°19,90 S and 25°49,70 E, 2907 m water depth) covering the last 350,000 years. We find distinct millennial scale events with high abundances of IRD in the sediments. Scanning-electron microscope analysis of individual grains shows a wide range of morphologies, with a high degree of angularity being a dominant feature, with surface microfeatures (linear fractures, grooves and troughs) that are typical for glacial origin and transport. We interpret these IRD events as indicators for a northward shift of the Southern Ocean frontal system, thereby allowing sufficient cooling and iceberg survivability as far north as the Agulhas Plateau. Our proxy record suggests significant millennial scale variability of the frontal movements throughout the last three glacial cycles. Largest IRD peaks occur during marine isotope stage 8 (~300 ka BP) and hence during a period for which an extreme northward shift in the STF has been identified previously (Bard and Rickaby, 2009). We compare our IRD record with records of millennial scale climate variability in the North Atlantic (McManus et al., 1999, Martrat et ... |
author2 |
non-UU output of UU-AW members |
format |
Article in Journal/Newspaper |
author |
Ziegler, M. Hall, I. R. Siret, P. J. Zahn, R. |
spellingShingle |
Ziegler, M. Hall, I. R. Siret, P. J. Zahn, R. Pleistocene ice-rafted debris events recorded at the Agulhas Plateau - indicators of intermittent Indian-Atlantic gateway closure |
author_facet |
Ziegler, M. Hall, I. R. Siret, P. J. Zahn, R. |
author_sort |
Ziegler, M. |
title |
Pleistocene ice-rafted debris events recorded at the Agulhas Plateau - indicators of intermittent Indian-Atlantic gateway closure |
title_short |
Pleistocene ice-rafted debris events recorded at the Agulhas Plateau - indicators of intermittent Indian-Atlantic gateway closure |
title_full |
Pleistocene ice-rafted debris events recorded at the Agulhas Plateau - indicators of intermittent Indian-Atlantic gateway closure |
title_fullStr |
Pleistocene ice-rafted debris events recorded at the Agulhas Plateau - indicators of intermittent Indian-Atlantic gateway closure |
title_full_unstemmed |
Pleistocene ice-rafted debris events recorded at the Agulhas Plateau - indicators of intermittent Indian-Atlantic gateway closure |
title_sort |
pleistocene ice-rafted debris events recorded at the agulhas plateau - indicators of intermittent indian-atlantic gateway closure |
publishDate |
2012 |
url |
https://dspace.library.uu.nl/handle/1874/396233 |
geographic |
Indian Southern Ocean |
geographic_facet |
Indian Southern Ocean |
genre |
North Atlantic South Atlantic Ocean Southern Ocean |
genre_facet |
North Atlantic South Atlantic Ocean Southern Ocean |
op_relation |
1029-7006 https://dspace.library.uu.nl/handle/1874/396233 |
op_rights |
info:eu-repo/semantics/OpenAccess |
_version_ |
1772185516805980160 |