A global climatic context (6.5 to 5 Ma) for the Mediterranean Messinian Salinity Crisis

Brown University, Providence RI

Investigators

Abstract

The global deep ocean circulation depends on the formation of dense waters that sink in the North Atlantic. Although these waters are not the coldest in the global ocean, they are salty enough to convect, forming a large-scale overturning that is an essential part of the global ocean heat and carbon "conveyor belt". One oceanographic theory posits the important contribution to this circulation of warm, salty water flowing out from the Mediterranean into the deep North Atlantic - the Mediterranean Outflow Water (MOW). Some climate models suggest that interrupting or altering the strength of the MOW would alter ocean heat transport and hence global temperature patterns. In this project, the research team will test the importance of the MOW using a natural geologic experiment when the connection between the Mediterranean and the Atlantic Ocean was completely cut off, a period of time known as the Messinian Salinity Crisis about 6 million years ago when the Mediterranean largely dried up and thick salt deposits were formed. Researchers will for the first time gather high resolution paleotemperature estimates at a number of open ocean sites using sediment sequences that span this time interval. If the MOW hypothesis is correct, the research will find a distinctive pattern of regional temperature responses during the time of Mediterranean isolation, followed by a shift when the connection to the open ocean was again established and MOW production resumed. Alternatively, if the hypothesized pattern of ocean surface temperature does not emerge, the research would suggest that the global importance of MOW has been overestimated. Sites have been selected for this study that span the Messinian and post-Messinian interval in the North Atlantic, central Atlantic, South Atlantic, and equatorial Pacific Oceans. Initial results show that sediment deposition is continuous at all sites through the time interval of interest. The research team will utilize organic alkenone paleothermometry in order to reconstruct ocean surface temperature evolution at approximately 3,000-year time steps from 6.5 to 5 million years ago at each site. This time period covers climate events that precede and post-date Mediterranean isolation. Sediment records will be correlated via oxygen isotope stratigraphy and orbital tuning so that they can be synchronized for comparison. Results will then be compared to climate models that simulate cessation of the MOW in order to verify/falsify the MOW hypothesis. The results will also be used as input for regional climate models of the Messinian interval in the Mediterranean region. This project will provide support for an early career female researcher and foster collaborations with an international community of researchers seeking to resolve the cause and effects of the Messinian Salinity Crisis. As part of the broader impacts of this work, undergraduates from Central Connecticut State University, a non-research institution with a high fraction of first-generation college students, will be recruited and mentored as summer interns. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.