Reconstruction of the Timing of Water Mass Exchange during Progressive Closure of the Central American Seaway in the Pliocene

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The goal of this project is to reconstruct the history of shallow, intermediate and deep water connections between the Caribbean Sea and the eastern Equatorial Pacific Ocean during the shoaling of the Central American Seaway (CAS) at the present location of Panama between 5.0 and 2.0 million years ago (Ma) using radiogenic isotopes. The progressive closure of the CAS and the associated reorganisation of ocean circulation have been controversially reported as contributing to a warming and a cooling of global climate, as well as increasing moisture supply to the northern hemisphere and hence preconditioning of the inception of Northern Hemisphere Glaciation. We propose to use the radiogenic isotopes of neodymium (Nd) and lead (Pb) as proxies to trace water masses and their mixing on either side of Panama. This study will use samples from ODP cores 999 and 1000 in the Caribbean and 1241 in the eastern tropical Pacific. In each core we will measure the Nd isotope composition of planktonic foraminiferal calcite in order to characterise surface water exchange and mixing, and the Nd and Pb isotope composition of early diagenetic ferromanganese coatings of the same sediment samples to characterise intermediate and deep water exchange and to assess differences and potential phase lags between surface and deeper water signatures. Sampling resolution will initially be at 100 thousand years (kyr), increasing to less than 21 kyr (i.e. sub-Milankovitch) for key periods identified in the 100 kyr resolution study. The aim of this project is to reconstruct the exact timing of CAS closure to deep, intermediate and shallow waters. These results will be compared with the evolution of the strength of North Atlantic Deep Water (NADW) formation and with the timing of changes in the distribution of heat and moisture to high northern latitudes. It will thus allow to better constrain causes and consequences during this key period of global climate evolution.