Pliocene North Atlantic water mass distribution and Meridional Overturning Circulation, 3.3 - 3.0 Ma
Final Report Abstract
This study focuses on a reconstruction of water mass distribution and an evaluation of AMOC strength during the Mid-Pliocene warm period ~3.3–3.0 Ma. In addition, the study was extended to focus on the reconstruction of North Atlantic deep water changes during the Plio/Pleistocene global cooling. Changes in North Atlantic deep water circulation during the past 4 Myr were studied at a suite of five IODP/ODP sites at water depths from ~2100 to 5000 m. Benthic δ13C records at these sites oscillate in parallel around values lower than today by 0.2‰ during interglacials and by 0.7‰ during glacials of the most recent Pliocene warm period 3.3–3.0 Myr ago. However, Mg/Ca-based bottom water temperatures were 2 to 3°C higher than today during interglacials and near modern levels during glacials. The coeval changes in ventilation at a lower level than today may indicate a weaker difference between these warm water masses than today, which is probably caused by vigorous water mixing. This is corroborated by εNd bottom water values near –9 to –10 at all sites, which differs markedly from the modern situation characterised by clear differences in εNd signatures between water masses at each site. Accordingly, the lesser ventilated, warm, and mixed water masses are most likely the result of the weaker overturning in the North Atlantic during that time of global warmth. After 1.6 Myr ago, benthic δ13C records show a gradually improving ventilation, with pronounced glacial/interglacial oscillations, which came close to the modern-to-late-Pleistocene levels. This ventilation change in deep water masses was coeval with a clear divergence in bottom water εNd between the different sites towards modern signatures. This is apparently linked to a significant change in the sources of circulating deep waters in the northern North Atlantic. Accordingly, the first reorganisation of North Atlantic deep water circulation towards the modern situation appears to have started only after 1.6 Myr ago, most likely as a response to increases in the amplitude of the Earth’s obliquity cycle during that time.
Publications
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(2011): Changes in North Atlantic deep water circulation during the past 4 Myr. AGU 2011, San Francisco, USA
Khélifi N., Frank M., and Nürnberg D.
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(2013): Changes in North Atlantic deep water circulation during the past 4 million years. ICP 11, Barcelona, Spain
Khélifi N., Frank M., and Nürnberg D.
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(2013): Reduced Atlantic circulation during the Pliocene warming? 2nd Workshop on Pliocene Climate, Bristol, UK
Khélifi N., Frank M., and Nürnberg D.
