Mediterranean Outflow Water variability during the Early Pleistocene

Stefanie Kaboth,Lucas Lourens,Patrick Grunert

doi:10.5194/cp-13-1023-2017

Abstract

Abstract. Gaining insights into the evolution of Mediterranean Outflow Water (MOW) during the Early Pleistocene has been so far hampered by the lack of available palaeoclimatic archives. Here we present the first benthic foraminifera stable oxygen and carbon isotope records and grain-size data from IODP Expedition 339 Site U1389 presently located within the upper core of the MOW in the Gulf of Cadiz for the time interval between 2.6 and 1.8 Ma. A comparison with an intermediate water mass record from the Mediterranean Sea strongly suggest an active MOW supplying Site U1389 on glacial–interglacial timescales during the Early Pleistocene. We also find indication that the increasing presence of MOW in the Gulf of Cadiz during the investigated time interval aligns with the progressive northward protrusion of Mediterranean sourced intermediate water masses into the North Atlantic, possibly modulating the intensification of the North Atlantic Meridional Overturning Circulation at the same time. Additionally, our results suggest that MOW flow strength was already governed by precession and semi-precession cyclicity during the Early Pleistocene against the background of glacial–interglacial variability.

Highlights

The Mediterranean Outflow Water (MOW) is a distinct hydrographic feature at intermediate water depths in the Gulf of Cadiz, distinguished from other ambient North Atlantic water masses by its warm and saline character (Fig. 1a; Ambar and Howe, 1979; Bryden et al, 1994; Bryden and Stommel, 1984)
Beyond the Mediterranean region, MOW has been acknowledged as an important modulator of the North Atlantic salt budget, with previous research suggesting that the absence of MOW may reduce Atlantic Meridional Overturning Circulation (AMOC) by as much as 15 % compared to modern conditions (Rogerson et al, 2006)
The δ18O difference between Site U1389 and the Mediterranean Sea is small during glacial periods in both investigated intervals, suggesting that Site U1389 bathed in MOW during these colder climatic conditions throughout the Early Pleistocene time interval (Fig. 4a)

Summary

Introduction

The Mediterranean Outflow Water (MOW) is a distinct hydrographic feature at intermediate water depths in the Gulf of Cadiz, distinguished from other ambient North Atlantic water masses by its warm and saline character (Fig. 1a; Ambar and Howe, 1979; Bryden et al, 1994; Bryden and Stommel, 1984). Despite its potential cosmopolitan significance, the palaeoceanographic history of MOW has so far been only studied for the Pliocene (Khelifi et al, 2009; Khélifi and Frank, 2014) and during the Late and Middle Pleistocene (Bahr et al, 2015; Kaboth et al, 2016, 2017; Llave et al, 2006; Schönfeld, 2002; Schönfeld and Zahn, 2000; Toucanne et al, 2007; Voelker et al, 2006)

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