Benthic foraminifera oxygen isotope chronology of IODP site 1386 and inferences for contourite depositions in the Gulf of Cádiz in relation to changes in Mediterranean Outflow Water (MOW) of the past 400 kyr.

Abstract

The role of Mediterranean Outflow Water (MOW) on the deposition of the Contourite Depositional System (CDS) is reasonably well understood, but its timing and strength remains controversial. As a consequence, changes in the characteristics of a CDS can be used to infer variations in ambient bottom water conditions. In this study a sediment core recovered from the Northern part of the Gulf of Cádiz is used to analyze two different proxies for the MOW, namely the benthic oxygen isotopes (δ 18Ob) and the >63 µm sediment fraction. These proxies are used to substantiate the presence of MOW related bottom currents and consequently determine times of increased and high energetic flow velocities during the last 400 ky, using δ 18Ob in addition for the construction of a reliable age model. Results of our study reveal an intensification of the MOW just before the deposition of sapropels in the Mediterranean, indicating that sapropel formation results in a drastic reduction if not termination of the MOW. Furthermore, a sudden decrease in the δ 18O record at the U1386 location indicates that there was still a warm pool present in the Mediterranean Sea during glacials.