Reconstruction of the Timing of Water Mass Exchange during Progressive Closure of the Central American Seaway in the Pliocene
Final Report Abstract
The project showed that uncleaned foraminifera in the EEP and Caribbean record the local bottom water εNd signal. A 12.5 Ma seawater εNd record was produced for ODP Site 1006 in the Florida Strait, allowing a long-term reconstruction of intermediate water circulation. The ODP 1000 record was also extended back into the Miocene. Both show a major shift from radiogenic εNd between 12 and 8 Ma to values around - 7 thereafter and indicate that the CAS had shoaled sufficiently to prevent the advection of Pacific waters into the Caribbean at intermediate water depths. Records of Pliocene seawater εNd were produced for the deep and intermediate Caribbean and showed an overall trend towards less radiogenic values. The EEP site showed no trend in seawater εNd during the Pliocene. The major change in deep Caribbean seawater εNd was finalized prior to ~ 7 Ma, likely directly linked to reduced Pacific inflow through the CAS. The changes in the Pliocene Caribbean are in contrast explained by increased inflow of Atlantic waters and an enhanced AMOC strength. High resolution examination of the deep Caribbean record during two time intervals, MIS M2 and MIS 95-100, reveal clear glacial-interglacial changes in REE compositions, particularly in the HREE/LREE and MREE/MREE* ratios and the Ce/Ce* anomaly. In contrast, the seawater εNd record does not show a cyclic change on G-IG timescales. During the MIS M2 glaciation, the REE compositions become more North Atlantic-like and are consistent with evidence of a reduction in a corrosive, southern source water mass, thus supporting an increase in the strength of the AMOC during sea-level induced closure of the CAS. During MIS 95-100, the HREE/LREE and MREE/MREE* records also support a larger contribution of northern-sourced waters to the deep Caribbean during the glaciations and these events occurred contemporaneously with episodes of complete CAS closure. However, on the basis of the Ce/Ce* anomaly and the carbonate sand record, the early parts of glaciations MIS 96, 98 and 100 were not as well ventilated as during MIS M2, which may indicate the presence of a poorly ventilated northern sourced water mass.
Publications
- (2014) Neodymium isotopes and concentrations in Caribbean seawater: Tracing water mass mixing and continental input in a semi-enclosed ocean basin. Earth and Planetary Science Letters 406, 174-186
Osborne, A.H., Haley, B.A., Hathorne, E.C., Floegel, S., Frank, M.
(See online at https://doi.org/10.1016/j.epsl.2014.09.011) - (2014) The neodymium and lead isotope record of the final stages of Central American Seaway closure. Paleoceanography
Osborne, A. H., Newkirk, D. R., Groeneveld, J., Martin, E. E., Tiedemann, R., Frank, M.
(See online at https://doi.org/10.1002/2014PA002676) - , 2015. Rare earth element distribution in Caribbean seawater: Continental inputs versus lateral transport of distinct REE compositions, Marine Chemistry
Osborne, A.H., Haley, B. A., Hathorne, E. C., Plancherel, Y., Frank, M.
(See online at https://doi.org/10.1016/j.marchem.2015.03.013)
