Vegetation And Organic-Walled Phytoplankton At The End Of The Antarctic Greenhouse World: Latest Eocene Cooling Events

The NBP0602A-3C SHALDRIL section collected in the Weddell Sea recovered a key stratigraphic interval that captured the response of plants and organic-walled phytoplankton during the first marked increase in delta O-18 followed by the large reduction in atmospheric CO2 in the late Eocene around 36 Ma. Well-preserved palynomorphs recovered from in situ shelf sediments provide evidence of a cooling event followed by a marked sea level drop around 36 Ma. Terrestrial palynomorphs indicate that at the time of deposition, southern beech-dominated and conifer forest vegetation was abundant but with lower diversity and signifying colder climates than for most of the La Meseta Formation on Seymour Island. The marine palynomorph assemblage is dominated by Vozzhennikovia apertura. This low-diversity, high-dominance dinoflagellate cyst assemblage is also a sign of deteriorating conditions. Particularly notable is the marked increase in the uppermost Eocene samples of reworked dinoflagellates and acritarchs of Cretaceous age. This suggests significant erosion and redeposition of nearby Campanian-Maastrichtian sections during a marked drop in sea level. Based on the biostratigraphy and a single isotopic date, it is likely that the cooling and subsequent lowering of sea level can be correlated to the brief spike in delta O-18-enriched values shown by the Zachos et al. (2001) curve in the Priabonian. According to Zachos et al. (2008), this event occurs at a time when lowest carbon dioxide atmospheric concentrations were between 600 and 980 ppmv, giving us some perspectives as to what could be expected when the current CO2 atmospheric concentration is at least doubled.