Millennial-scale reconstruction of Orinoco run-off strength and its impact on the Atlantic Meridional Overturning Circulation (MORA)

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Climate models as well as paleoenvironmental studies demonstrate that moisture availability in the hinterland of the Caribbean and, hence, river run-off into the Caribbean Sea is highly sensitive to climatic changes. Changes of the hydrological cycle in northern South America will not only impact the local water budget but might have far-reaching consequences: Caribbean surface water is an important mediator of the salt budget of the Gulf Stream and thereby preconditions high-latitude deep water formation. Caribbean surface salinities altered by changes in the freshwater input might therefore ultimately affect the strength of the Atlantic Meridional Overturning Circulation and, consequently, global climate. Despite the clear relevance of this phenomenon, no attempts have been made to reconstruct Holocene and Last Glacial runoff of major rivers into the Caribbean Sea in high temporal resolution. In the proposed project we want to close this gap by generating Last Glacial to Holocene (semi)quantitative estimates of Orinoco discharge in millennial-scale resolution. The base of the study will be foraminiferal Ba/Ca and δ18Oseawater measurements as locally calibrated proxies for river input and salinity changes in cores located close to the Orinoco Delta. A comparison with records from the Amazon Delta, Caribbean, Gulf of Mexico and Northern Atlantic will show whether anomalously high or low Orinoco/Amazon discharge is changing surface ocean salinity on a large scale and thereby represents a previously underestimated factor within the ocean/climate system.