Deciphering the paleoceanographic and paleoclimatic changes of the Gulf of Cádiz during the past 2.6 million years

Abstract

This thesis aims to shed new light on the climatic dependent evolution of Mediterranean Outflow Water throughout the Pleistocene epoch which comprises the last ~2.6 million years.Our findings show for the Late Pleistocene and Holocene time interval (last 600.000 years) three distinct phases of MOW composition and flow strength variability along the upper slope of the Gulf of Cadiz. On one hand, these changes are associated with the glacial density increase of the MOW driven by the shallowing of the Gibraltar Strait causing a salinity increase of the Mediterranean Sea itself. On the other hand, the observed changes also relate to variability in the water mass sourcing of the MOW by stronger contributions of the denser western Mediterranean deep-water alongside potential tectonic modulation of the MOW flow path within the Gulf of Cadiz. Moreover, the results show a inverse relationship of the Mediterranean outflow water to monsoonal freshwater inputs into the Eastern Mediterranean forced by changes in the precession of the Earth`s rotation axis (~23.000 year timescales). An enhanced East African Monsoon leads to an increased river runoff of the Nile which weakens the formation of Mediterranean outflow waters. The results also show that the distinct stable oxygen isotope enrichment events documented in the time interval between 150.000 and 300.000 years coincide with substantial ice advance periods on continental Europe (Drenthe and Fuhne) and pre-date “cooling events” along the Iberian Margin linked to European sourced meltwater pulses. Finally, the findings of this thesis suggest Mediterranean outflow activity along the middle slope already during the Early Pleistocene and that it was predominately sourced by eastern Mediterranean intermediate water masses similar to modern conditions. The documented increasing of MOW in the Gulf of Cadiz during the Early Pleistocene is potentially related to the intensification of the North Atlantic Meridional Overturning Circulation at the same time.