From North Africa to the North Atlantic Ocean via the Mediterranean Sea: a journey through high-resolution palaeorecords and sub-precessional numerical simulations

Alice Marzocchi, University of Chicago, Geophysical Sciences, Chicago, IL, United States, Rachel Flecker, University of Bristol, Bristol, United Kingdom, Dan John Lunt, University of Bristol, School of Geographical Sciences and Cabot Institute, Bristol, BS8, United Kingdom, Tanja J Kouwenhoven, Utrecht University, Netherlands, Wout Krijgsman, Utrecht University, Paleomagnetic Laboratory “Fort Hoofddijk”, Utrecht, Netherlands, Frits J Hilgen, Utrecht University, Stratigraphy and Paleontology, Utrecht, Netherlands and Jan Peter Mayser, Organic Geochemistry Unit, School of Chemistry, University of Bristol, Bristol, United Kingdom
Abstract:
Mid-latitudes marginal marine seas like the Mediterranean are highly sensitive to regional climatic change. This is a consequence of their nearly land-locked configuration, which reduces the ocean’s buffering effect. In these semi-enclosed basins, the rapid response to local changes and the relatively high sedimentation rates can produce high-resolution palaeoclimatic records. The high quality of these reconstructions is used to understand the basin’s environmental variability and its evolution through time.

Mediterranean sedimentary successions of the last ten million years commonly contain a pronounced cyclicity, which is thought to be orbitally-driven, dominantly by climatic precession. However, most of the hypotheses relating the phasing of the sedimentary record to the orbital forcing are still largely untested. The combination of field-based observations with numerical modelling allows us to investigate the mechanisms driving climatic changes, in and around the basin, on sub-precessional time scales.

Using an example from a modelled late Miocene precession cycle (22 simulations with a general circulation model, equally-spaced in time, centred around 6.5 Ma) we illustrate how environmental changes in the Mediterranean Sea are driven by the basin's hydrologic fluxes (e.g. exchange with the Atlantic Ocean and Black Sea ocean-basin, evaporation, rainfall and runoff). Where exchange with the open ocean is restricted, changes in the hydrologic budget can drive large salinity fluctuations, triggering both a lithological and faunal response. This information is preserved in the late Miocene geological record of the Mediterranean Sea and our sub-precessional model output can be directly compared with available high-resolution geological data, such as microfaunal assemblages. This allows us to test the biogeochemical phasing of Mediterranean successions in relation to orbital changes.

Here, we demonstrate that the precessional signal in the Mediterranean Sea originates both from monsoonal rainfall from the North African catchments and from the activity of the North Atlantic storm tracks. We also discuss to what extent this climate signal, amplified by the Mediterranean, penetrates further afield via gateway exchange and potentially influences global ocean circulation.

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