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Climate of the Past An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/cp-2017-134
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
20 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).
Variations of Mediterranean–Atlantic exchange across the late Pliocene climate transition
Ángela García-Gallardo, Patrick Grunert, and Werner E. Piller Institute of Earth Sciences, University of Graz, NAWI Graz Geocenter, Heinrichstrasse 26, 8010 Graz, Austria
Abstract. Mediterranean-Atlantic exchange through the Strait of Gibraltar plays a significant role in the global ocean-climate dynamics in two ways. On one side, the injection of the saline and warm Mediterranean Outflow Water (MOW) contributes to North Atlantic deep-water formation. In return, the Atlantic inflow is considered a sink of less saline water for the North Atlantic Ocean. However, while the history of MOW is the focus of numerous studies, the latter has received little attention so far. The present study provides an assessment of the Mediterranean–Atlantic exchange with focus on the Atlantic inflow strength and its response to regional and global climate from 3.33 to 2.60 Myrs. This time interval comprises the mid-Pliocene warm period (MPWP, 3.29–2.97 Myr) and the onset of the Northern Hemisphere Glaciation (NHG). For this purpose, gradients in surface δ18O records of the planktonic foraminifer Globigerinoides ruber between the Integrated Ocean Drilling Program (IODP) Hole U1389E (Gulf of Cadiz) and ODP Site 978 (Alboran Sea) have been evaluated. Interglacial stages and warm glacials of the MPWP revealed steep and reversed (relative to the present) W-E δ18O gradients suggesting a weakening of Mediterranean–Atlantic exchange likely caused by high levels of relative humidity in the Mediterranean region. In contrast, periods of stronger inflow are indicated by flat δ18O gradients due to more intense arid conditions during the severe glacial Marine Isotope Stage (MIS) M2 and the initiation of the NHG (MIS G22, G14, G6–104). Intensified Mediterranean–Atlantic exchange in cold periods is linked to the occurrence of ice-rafted debris (IRD) at low latitudes and weakening of the Atlantic Meridional Overturning Circulation (AMOC). Our results thus suggest the development of a negative feedback between AMOC and exchange rates at the Strait of Gibraltar in the latest Pliocene as it has been proposed for the late Quaternary.

Citation: García-Gallardo, Á., Grunert, P., and Piller, W. E.: Variations of Mediterranean–Atlantic exchange across the late Pliocene climate transition, Clim. Past Discuss., https://doi.org/10.5194/cp-2017-134, in review, 2017.
Ángela García-Gallardo et al.
Ángela García-Gallardo et al.
Ángela García-Gallardo et al.

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Short summary
We study the variability of Mediterranean–Atlantic exchange with focus on the surface Atlantic inflow across the mid-Pliocene warm period and the onset of the Northern Hemisphere Glaciation, still unresolved by previous works. Oxygen isotope gradients between both sides of the Strait of Gibraltar reveal weak inflow during warm periods that turns stronger during severe glacials and the start of a negative feedback between exchange at the Strait and the Atlantic Meridional Overturning Circulation.
We study the variability of Mediterranean–Atlantic exchange with focus on the surface Atlantic...
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