Climate-induced variability in Mediterranean outflow to the North Atlantic Ocean during the late Pleistocene

• Main Authors: Nichols, Matthew, Xuan, Chuang, Crowhurst, Simon, Hodell, David A., Richter, Carl, Acton, Gary, Wilson, Paul A.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2020
• Subjects: North Atlantic
• Online Access: https://eprints.soton.ac.uk/443243/; https://eprints.soton.ac.uk/443243/1/877556_1_merged_1596657904.pdf; https://eprints.soton.ac.uk/443243/2/2020PA003947.pdf

Mediterranean Outflow Water (MOW) adds salt and density to open ocean intermediate waters and is therefore an important motor of Atlantic meridional overturning circulation (AMOC) and climate variability. However, the variability in strength and depth of MOW on geological timescales is poorly documented. Here we present new detailed records, with excellent age control, of MOW variability from 416 ka to present from rapidly accumulated marine sediments recovered from the West Iberian Margin during Integrated Ocean Drilling Program (IODP) Expedition 339. Our records of x-ray fluorescence (XRF), physical grain size and palaeocurrent information from the anisotropy of magnetic susceptibility (AMS) indicate (i) a close relationship between the orientation of principle AMS axes and glacial-interglacial cycles and (ii) two distinct regimes of MOW behaviour over the last ~416 kyrs in grain size and AMS variability at orbital (mainly precessional) and suborbital timescales. Between marine isotope stages (MIS) 10 and MIS 4, MOW was focused at a generally shallow depth on the West Iberian Margin, and changes in MOW strength were strongly paced by precession. A transition interval occurred during MIS 5 and 4, when MOW deepened and millennial-scale variability in strength flow strength was superimposed on orbitally paced change. During MIS 11 and from MIS 3 to present, MOW was deeply focused and millennial-scale variability dominated. We infer that late Pleistocene variability in MOW strength and depth were strongly climate- influenced and that changes in circum-Mediterranean rainfall climate were likely a primary control.