Exploring the mechanism of Mediterranean overturning circulation using the sedimentary record and conceptual box models

The well-dated and extensively studied Quaternary sedimentary record of the Mediterranean basin provides valuable insight into the dynamics of the basin. From this wealth of data, we try to achieve mechanistic understanding of the overturning circulation using conceptual box models. An outstanding aspect of the stratigraphic record are organic-rich deposits called sapropels. These deposits are excellent examples of sudden, strong responses to long-term climate variability. Sapropels are found (semi-)periodically for the last 13.5 million years, most prominently in the eastern basin. There is a strong correlation between the timing of the formation of sapropels and periods of North African monsoon intensification. This correlation strongly supports the hypothesis that increased freshwater input has resulted in prolonged periods of buoyancy gain and subsequent weakening or collapse of deep-water formation. The focus of this study is to explain the more intensely developed sapropel records in the eastern basin compared to the western basin.  Specifically, we will address whether the geographical setting of the eastern basin alone can account for sapropel formation.  

Where state-of-the-art Global Climate Models (GCMs) or high-resolution ocean models are able to capture the complex dynamics of the Mediterranean Sea, they are generally computationally demanding and are not suitable to perform long-duration (~100 kyr or longer) simulations. Consequently, either only snapshot studies are available or the spatial resolution is greatly reduced. Conceptual climate models or box models may offer us important new insights. With box models, we try to analyse the physical processes of the Mediterranean overturning circulation and related deep-water formation events. As such, we pay special attention to the forcings required for initiation and stagnation of the overturning circulation and deep water formation. A major benefit of using box models is that they are computationally efficient and that therefore they allow us to test and simulate a large range of configurations and parameter combinations. In addition, we are able to study the transient response to changes in the climate instead of only snapshots. In an important step forward from previous modelling studies, we make a distinction between the western- and eastern basin.