Impacts of the Mediterranean Outflow variability upon North Atlantic circulation

BOSCORF has recently completed a large ITRAX scanning project with Matt Nichols, currently a second year PhD at Southampton. Here Matt details how he will be using the Ca/Ti ratio to refine the age model for his core, and the importance of XRF data in this study.


Mediterranean outflow water (MOW) leaking into the Atlantic Ocean has been shown to significantly affect Atlantic meridional overturning circulation (AMOC), one of the main long-term drivers of heat distribution to the northern Hemisphere. As AMOC is driven by the sinking of cold, dense water in the high latitudes, the additional salinity provided by saline Mediterranean water enhances the rate of North Atlantic deep-water formation and thereby the overall rate of overturning and heat transport. At times of AMOC stagnation and freshening, the MOW has particular significance by increasing the salinity of intermediate depth Atlantic waters and helping to re-instate vigorous overturning1.

 Figure showing the path and depth of the Mediterranean outflow in the North East Atlantic4.

This project incorporates data from sediments from International Ocean Discovery Programme (IODP) Sites U1391, U1385 and U1390, collected during Expedition 339 to the Iberian Margin2. Sediments on the Iberian Margin and the Gulf of Cadiz record changes in AMOC and the MOW through the mid to late Pleistocene (the last ~1 million years).

Grain size and sediment composition changes Sites U1391 and U1390 can provide insight into MOW strength variability and migration up and down slope, while Site U1385 has remarkable oxygen isotope records that closely resemble changes in both the Greenland and Antarctic ice core temperature records, in the surface and bottom water respectively. By high resolution correlation of these climate records we can further understand how MOW has impacted upon AMOC on both short timescales and through differing climate settings.

A strong age-model is critical to this study as confidence will be needed in any millennial scale lags and leads between various MOW and AMOC proxies. By high-resolution scanning of a suite of 60 u-channels from Site U1391 on the ITRAX XRF scanner at BOSCORF we can transfer the well-established age model of Site U13853 to Site U1391 by correlation of Ca/Ti data between the two sites. Additionally, invaluable grain size (Zr/Rb) and sediment composition data can be gleaned from the XRF data which will help to determine MOW strength changes and sediment provenance.


1. Voelker et al., 2006. Mediterranean outflow strengthening during northern hemisphere coolings: A salt source for the glacial Atlantic? Earth and Planetary Science Letters, 245, 39-55.

2. Expedition 339 Scientists, 2012. Mediterranean outflow: environmental significance of the Mediterranean Outflow Water and its global implications. IODP Prel. Rept., 339.

3. Hodell et al., 2015. A reference time scale for Site U1385 (Shackleton Site) on the SW Iberian Margin. Global and Planetary Change, 133, 49-64.

4. Khélifi et al 2014. Late Pliocene variations of the Mediterranean outflow. Marine Geology, 357, 182-194.