Palaeoclimate reconstruction of the last greenhouse-icehouse transition based on geochemical and micropalaeontological records from Central Mississippi, US Gulf Coastal Plain

• Main Author: De Lira Mota, Marcelo Augusto
• Other Authors: Dunkley Jones, Tom, Bendle, James, other
• Format: Thesis
• Language: English; Portuguese
• Published: 2020
• Subjects: QE Geology; East Antarctica; Southern Ocean; Antarc*; Antarctica; Ice Sheet
• Online Access: http://etheses.bham.ac.uk//id/eprint/10423/3.hassmallThumbnailVersion/DeLiraMota2020PhD.pdf; http://etheses.bham.ac.uk//id/eprint/10423/; http://etheses.bham.ac.uk//id/eprint/10423/3/DeLiraMota2020PhD.pdf; http://etheses.bham.ac.uk//id/eprint/10423/2/DeLiraMota2020PhD_supplementarymaterial.xlsx

During the Eocene-Oligocene Transition (EOT; ~34.4-33.7 Ma), the Earth experienced a major shift in climate state, from so called “greenhouse” to “icehouse” conditions, with the first formation of the modern continental-scale ice sheet on Antarctica (Oi-1 event: ~33.7 Ma). This transition was associated with deep-sea cooling, glacioeustatic sea level fall, worldwide regressions, along with major disturbances in the global carbon cycle and ecosystems. To investigate this climatic disruption, high- resolution coccolith fraction (<20 μm) carbonate stable oxygen (δ18O) and carbon (δ13C) isotope records (~7 ka resolution), palynological and calcareous nannofossil assemblage (~26 ka resolution) records, and bulk sediment X-ray fluorescence analyses (<10 ka resolution) have been generated from a continuously cored (~137 m) and substantially expanded (~4.7 cm ka-1) succession of upper Eocene-lower Oligocene (~4 Ma) mid-shelf marine clays from the central Mississippi, US Gulf Coastal Plain – the Mossy Grove Core (MGC). Based on a refined age-depth model, this multiproxy analysis revealed that the increasing export of nutrients from the Southern Ocean to the tropical and sub-tropical oceans enhanced marine primary production in these regions, further leading to increased sequestration of atmospheric CO2 through an invigorated biological pump. We also found evidence that extraterrestrial impacts may have induced sulfate-aerosol-driven climate forcing, triggering positive feedback mechanisms, and intensifying and/or sustaining the cooling. Further analysis also demonstrated that a significant sea level fall (~34.5 Ma) preceded the Oi-1 event by ~800 ka and represents the first stage of large-scale expansion of the East Antarctica Ice Sheet. This challenges the current view that the dynamics of the EOT are dominated by global cooling during the earliest stages, which then precondition the system to continental-scale ice-sheet expansion in the later stages. We also propose that the earliest stages of the major EOT eustatic sea-level fall had a disproportionate effect on global biogeochemistry, by causing the first major incision of organic- and nutrient-rich coastal low lands that had been accreting under warm, high sea-level greenhouse conditions for tens of millions of years.