Abstract:
During the Pliocene major changes in global climate and oceanography occurred due to closure of the Central American Seaway (CAS) and the intensification of Northern Hemisphere glaciations. Currently, many outstanding questions remain regarding the re-organization of oceanic circulation during this time. Here, we apply a multiproxy approach to examine sediments from Site U1396 from IODP Expedition 340 (Lesser Antilles Volcanism and Landslides), situated in the eastern Caribbean, which presently falls under in the influence of the North Equatorial Current. This site presents an excellent opportunity to test both the new tropical planktic foraminiferal biostratigraphic calibration of Wade et al., 2011 and to investigate the temperature of the past approximately 4.52 myr from the Montserrat region. After correlating Holes A and C, planktic results largely corroborate the order of bioevents from Wade et al., 2011, however secondary marker species Globorotalia flexuosa, Gr. crassaformis, and Gr. pertenuis have lowest occurrences that extend below their expected First Appearance datums, while Globigerinoides extremus and Pulleniatina primalis were found to have anomalously high ranges reflecting regional influences. Sedimentation rates derived from this revised Hole U1396-A and -C biostratigraphy show the same trend as shipboard work: faster sedimentation in the lower Pliocene, slowing towards the Holocene. Two organic geochemical paleothermometers, the U (super k) (sub 37) Index and TEX (super H) (sub 86) , were utilized to examine Plio-Pleistocene SST variability. While the U (super k) (sub 37) Index is at unity in many samples and is thus somewhat insensitive to temperature change at this tropical site, the TEX (super H) (sub 86) record displays more variability. A significant cooling is noted in TEX (super H) (sub 86) SST at approximately 4.1 Ma based on the preliminary age model, coinciding with significant changes in foraminiferal abundance, which may be related to changes in ocean circulation associated with an important transition in the closure of the central American Seaway (e.g., Steph et al., 2010). Overall, application of organic geochemical paleothermometers appears to be a promising technique for examining the Pliocene SST evolution of the Caribbean, particularly since these proxies are not influenced by salinity to the extent observed in delta (super 18) O or Mg/Ca ratios of foraminifera.