Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean
Pelagic sediments from the subtropical South Atlantic Ocean contain geographically extensive Oligocene ooze and chalk layers that consist almost entirely of the calcareous nannofossil Braarudosphaera. Poor recovery and the lack of precise dating of these horizons in previous studies has limited the...
Published in: | Paleoceanography and Paleoclimatology |
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2018
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Online Access: | http://hdl.handle.net/11564/701376 https://doi.org/10.1002/2017PA003222 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017PA003222 |
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ftunivchietiiris:oai:ricerca.unich.it:11564/701376 2024-04-21T08:11:34+00:00 Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean D. Liebrand I. Raffi A. Fraguas R. Laxenaire J. H. C. Bosmans F. J. Hilgen P. A. Wilson S. J. Batenburg H. M. Beddow S. M. Bohaty P. R. Bown A. J. Crocker C. E. Huck L. J. Lourens L. Sabia Liebrand, D. Raffi, I. Fraguas, A. Laxenaire, R. Bosmans, J. H. C. Hilgen, F. J. Wilson, P. A. Batenburg, S. J. Beddow, H. M. Bohaty, S. M. Bown, P. R. Crocker, A. J. Huck, C. E. Lourens, L. J. Sabia, L. 2018 ELETTRONICO http://hdl.handle.net/11564/701376 https://doi.org/10.1002/2017PA003222 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017PA003222 eng eng info:eu-repo/semantics/altIdentifier/pmid/31058259 info:eu-repo/semantics/altIdentifier/wos/WOS:000435281200006 volume:33 issue:5 firstpage:511 lastpage:529 numberofpages:19 journal:PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY http://hdl.handle.net/11564/701376 doi:10.1002/2017PA003222 info:eu-repo/semantics/altIdentifier/scopus/2-s2.0-85047664229 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017PA003222 info:eu-repo/semantics/openAccess Braarudosphaera acme Oligocene astronomical forcing of atmospheric and oceanic front eddie monsoon surface ocean stratification info:eu-repo/semantics/article 2018 ftunivchietiiris https://doi.org/10.1002/2017PA003222 2024-03-25T01:49:22Z Pelagic sediments from the subtropical South Atlantic Ocean contain geographically extensive Oligocene ooze and chalk layers that consist almost entirely of the calcareous nannofossil Braarudosphaera. Poor recovery and the lack of precise dating of these horizons in previous studies has limited the understanding of the number of acmes, their timing and durations, and therefore their likely cause. Here we present a high-resolution, astronomically tuned stratigraphy of Braarudosphaera oozes (29.5-27.9 Ma) from Ocean Drilling Program Site 1264 in the southeastern Atlantic Ocean. We identify seven episodes with highly abundant Braarudosphaera. Four of these acme events coincide with maxima and three with minima in the ~110 and 405-kyr paced eccentricity cycles. The longest lasting acme event corresponds to a pronounced minimum in the ~2.4-Myr eccentricity cycle. In the modern ocean, Braarudosphaera occurrences are limited to shallow marine and neritic settings, and the calcified coccospheres of Braarudosphaera are probably produced during a resting stage in the algal life cycle. Therefore, we hypothesize that the Oligocene acmes point to extensive and episodic (hyper) stratified surface water conditions, with a shallow pycnocline that may have served as a virtual seafloor and (partially/temporarily) prevented the coccospheres from sinking in the pelagic realm. We speculate that hyperstratification was either extended across large areas of the South Atlantic basin, through the formation of relatively hyposaline surface waters, or eddy contained through strong isopycnals at the base of eddies. Astronomical forcing of atmospheric and/or oceanic circulation could have triggered these conditions through either sustained rainfall over the open ocean and adjacent land masses or increased Agulhas Leakage. Article in Journal/Newspaper South Atlantic Ocean ARUd'A - Archivio Istituzionale della ricerca dell'università Chieti-Pescara (IRIS) Paleoceanography and Paleoclimatology 33 5 511 529 |
institution |
Open Polar |
collection |
ARUd'A - Archivio Istituzionale della ricerca dell'università Chieti-Pescara (IRIS) |
op_collection_id |
ftunivchietiiris |
language |
English |
topic |
Braarudosphaera acme Oligocene astronomical forcing of atmospheric and oceanic front eddie monsoon surface ocean stratification |
spellingShingle |
Braarudosphaera acme Oligocene astronomical forcing of atmospheric and oceanic front eddie monsoon surface ocean stratification D. Liebrand I. Raffi A. Fraguas R. Laxenaire J. H. C. Bosmans F. J. Hilgen P. A. Wilson S. J. Batenburg H. M. Beddow S. M. Bohaty P. R. Bown A. J. Crocker C. E. Huck L. J. Lourens L. Sabia Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean |
topic_facet |
Braarudosphaera acme Oligocene astronomical forcing of atmospheric and oceanic front eddie monsoon surface ocean stratification |
description |
Pelagic sediments from the subtropical South Atlantic Ocean contain geographically extensive Oligocene ooze and chalk layers that consist almost entirely of the calcareous nannofossil Braarudosphaera. Poor recovery and the lack of precise dating of these horizons in previous studies has limited the understanding of the number of acmes, their timing and durations, and therefore their likely cause. Here we present a high-resolution, astronomically tuned stratigraphy of Braarudosphaera oozes (29.5-27.9 Ma) from Ocean Drilling Program Site 1264 in the southeastern Atlantic Ocean. We identify seven episodes with highly abundant Braarudosphaera. Four of these acme events coincide with maxima and three with minima in the ~110 and 405-kyr paced eccentricity cycles. The longest lasting acme event corresponds to a pronounced minimum in the ~2.4-Myr eccentricity cycle. In the modern ocean, Braarudosphaera occurrences are limited to shallow marine and neritic settings, and the calcified coccospheres of Braarudosphaera are probably produced during a resting stage in the algal life cycle. Therefore, we hypothesize that the Oligocene acmes point to extensive and episodic (hyper) stratified surface water conditions, with a shallow pycnocline that may have served as a virtual seafloor and (partially/temporarily) prevented the coccospheres from sinking in the pelagic realm. We speculate that hyperstratification was either extended across large areas of the South Atlantic basin, through the formation of relatively hyposaline surface waters, or eddy contained through strong isopycnals at the base of eddies. Astronomical forcing of atmospheric and/or oceanic circulation could have triggered these conditions through either sustained rainfall over the open ocean and adjacent land masses or increased Agulhas Leakage. |
author2 |
Liebrand, D. Raffi, I. Fraguas, A. Laxenaire, R. Bosmans, J. H. C. Hilgen, F. J. Wilson, P. A. Batenburg, S. J. Beddow, H. M. Bohaty, S. M. Bown, P. R. Crocker, A. J. Huck, C. E. Lourens, L. J. Sabia, L. |
format |
Article in Journal/Newspaper |
author |
D. Liebrand I. Raffi A. Fraguas R. Laxenaire J. H. C. Bosmans F. J. Hilgen P. A. Wilson S. J. Batenburg H. M. Beddow S. M. Bohaty P. R. Bown A. J. Crocker C. E. Huck L. J. Lourens L. Sabia |
author_facet |
D. Liebrand I. Raffi A. Fraguas R. Laxenaire J. H. C. Bosmans F. J. Hilgen P. A. Wilson S. J. Batenburg H. M. Beddow S. M. Bohaty P. R. Bown A. J. Crocker C. E. Huck L. J. Lourens L. Sabia |
author_sort |
D. Liebrand |
title |
Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean |
title_short |
Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean |
title_full |
Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean |
title_fullStr |
Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean |
title_full_unstemmed |
Orbitally Forced Hyperstratification of the Oligocene South Atlantic Ocean |
title_sort |
orbitally forced hyperstratification of the oligocene south atlantic ocean |
publishDate |
2018 |
url |
http://hdl.handle.net/11564/701376 https://doi.org/10.1002/2017PA003222 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017PA003222 |
genre |
South Atlantic Ocean |
genre_facet |
South Atlantic Ocean |
op_relation |
info:eu-repo/semantics/altIdentifier/pmid/31058259 info:eu-repo/semantics/altIdentifier/wos/WOS:000435281200006 volume:33 issue:5 firstpage:511 lastpage:529 numberofpages:19 journal:PALEOCEANOGRAPHY AND PALEOCLIMATOLOGY http://hdl.handle.net/11564/701376 doi:10.1002/2017PA003222 info:eu-repo/semantics/altIdentifier/scopus/2-s2.0-85047664229 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017PA003222 |
op_rights |
info:eu-repo/semantics/openAccess |
op_doi |
https://doi.org/10.1002/2017PA003222 |
container_title |
Paleoceanography and Paleoclimatology |
container_volume |
33 |
container_issue |
5 |
container_start_page |
511 |
op_container_end_page |
529 |
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1796953551439659008 |