Gulf Stream hydrography during the Late Pliocene/Early Pleistocene: low versus high latitude forcing of the Atlantic Meridional Overturning Circulation
Mineralogy, Petrology and Geochemistry
Oceanography
Final Report Abstract
The new planktic d18O data from Site 1006 indicate that there was a change in surface water properties of the Gulf Stream during the late Pliocene and early Pleistocene, but also showed that these were not linked to changes in the Caribbean Warm Pool, which themselves likely occurred in response to glacially-driven CAS opening and closure episodes. Rather, the planktic d18O results show that there was a shift from subtropical-gyre like variability in the late Pliocene to precessionally-paced variability in the early Pleistocene, suggesting a shift to low latitude forcing, which is more like the modern situation. Evidence for an active Loop Current during the early Pleistocene is provided by the negative peaks in planktic d18O in both the Gulf of Mexico and the Florida Strait, which are attributed to Mississippi-Laurentide meltwater events. These planktic d18O excursions are not seen in the Central Caribbean record of ODP Site 999. The main factor controlling the seawater Nd-isotope composition at Site 1006 was different for each of the three time intervals investigated. Close correspondence between changes in Nd-isotope composition, manganese content and the percentage of aragonite suggest that the supply of aragonite from the Great Bahama Bank controlled the seawater Nd-isotope composition during the early Pliocene. The late Pliocene Nd-isotope records from ODP 1000 and 1006 complete a section through the Caribbean and Florida Strait starting at Site 999. All three records show small, contemporaneous variability, strongly suggesting that the seawater Nd-isotope composition was an advected signal at this time. There was no change in Nd-isotope composition during the MIS M2 glaciation, when the CAS was likely closed to Pacific waters, and there is consequently no evidence that there was a change in intermediate water circulation. There were likewise no glacial-interglacial changes in the intermediate water composition at Site 1000 during the early Pleistocene. The Florida Strait record for the early Pleistocene largely resembles those of the central and northern Caribbean, suggesting that, as for the late Pliocene, the Ndisotope composition was predominantly an advected signal. However, three extremely negative Nd-isotope excursions in the Site 1006 record indicate that there were, at least intermittently, other factors at play. Extremely negative Nd-isotope compositions were also measured in the detrital fraction, strongly suggesting that this terrigenous material contributed to the seawater Nd-isotope composition, at least locally. Combining the Nd- and Sr-isotope composition of the detrital fraction shows that they plot well outside the range of known possible terrigenous sources in the area. The excursions occurred during the rising limb of freshwater pulses as recorded in the Gulf of Mexico and are likely associated with the meltwater transport of clays from an as yet unidentified source.
Publications
- (2016) Gulf Stream hydrography during the late Pliocene/early Pleistocene: low versus high latitude forcing of the Atlantic Meridional Overturning Circulation. IODP/ICDP Kolloquium 2016, 14.-16.03 2016, Heidelberg, Germany
Osborne, A. H., and Frank, M.
- Rare earth element patterns in sedimentary foraminifera: potential water mass tracers? ASLO 2017, 26.02-03.03 2017, Honolulu, Hawaii, USA
Osborne, A. H.; Hathorne, E. C.; Plancherel, Y.; Schijf, J; Böning, P.; Frank, M.
- (2019) Gulf Stream Hydrography during the Pliocene/early Pleistocene: low versus high latitude forcing of the Atlantic Meridional Overturning Circulation. IODP/ICDP Kolloquium 2019, 18.-20.03 2019, Cologne, Germany
Osborne, A. H.; Frank, M.; Kroon, D.; Wright, J. D.; Gutjahr, M.; Reuning, L.
- (2019), Late Pliocene and Early Pleistocene Variability of the REE and Nd Isotope Composition of Caribbean Bottom Water: A Record of Changes in Sea Level and Terrestrial Inputs During the Final Stages of Central American Seaway Closure, Paleoceanography and Paleoclimatology
Osborne, A. H., E. C. Hathorne, P. Boning, J. Groeneveld, K. Pahnke, and M. Frank
(See online at https://doi.org/10.1029/2019PA003654) - (2019), Miocene restriction of the Pacific-North Atlantic throughflow strengthened Atlantic overturning circulation, Nature Communications
Kirillova, V., A. H. Osborne, T. Storling, and M. Frank
(See online at https://doi.org/10.1038/s41467-019-12034-7) - (2019). Miocene to early Pleistocene variations in Gulf Stream hydrography and their impact on the Atlantic Meridional Overturning Circulation. In: ICP13 2019, 2.-6.09 2019, Sydney, Australia
Osborne, A. H.; Kirillova, V.; Hathorne, E. C.; Störling, T.; Kroon, D.; Böning, P.; Groeneveld, J.; Gutjahr, M.; Reuning, L.; Pahnke, K.; Tiedemann, R.; Wright, J., D.; Frank, M.
