| dc.description.abstract | Last time in Earth’s history when atmospheric CO2 was comparable or slightly higher than at present was during the early Late Pliocene (3.6 to 3.0 Ma). During this generally warm period, one intense glaciation occurred (known as M2, lasting between 3.312 and 3.264 Ma), followed by the mid-Piacenzian Warm Period. The transition from M2 to the mid-Piacenzian Warm Period is often seen as an analogue for the climate of our (near) future. The end of the mid-Piacenzian Warm Period started with the less intense G20 glacial (3.025 Ma), followed by other less intense glacials. This study focuses on a marine sediment record from ODP Site 625 taken offshore the Mississippi delta, which is, therefore, expected to contain both marine and terrestrial material. The aim of this study is to reconstruct the terrestrial (hydro)climate and associated Mississippi input into the Gulf of Mexico (GoM) as well as the oceanographic changes in the Gulf of Mexico during two glacial periods: M2 and the less intense G20 using a multi-proxy approach of both lipid biomarkers and palynology. The absence of plant- and soil-derived lipid biomarkers and pollen in the sediments indicate that terrestrial material discharged to the ocean by the Mississippi did not reach the site location during the studied intervals. On the other hand, marine lipid biomarkers and dinoflagellate cysts reveal a strong influence of the Loop Current during the interval preceding M2, transporting warm and salty Caribbean waters into the Gulf of Mexico. During the cold M2 interval, TEX86 sea surface temperatures dropped from 22.7°C to 20.6°C and Uk37 sea surface temperatures from 27.2°C to 26.2°C. During the temperature drop, salinity and stratification of the water column increased, eventually resulting in hyperstratification, as indicated by the presence of P. zoharyi. Hyperstratification still lasted into the following mid-Pliocene Warm Period, at least until 3.247 Ma. Eventually, the change in dinocyst composition shows that Caribbean waters entered the northern Gulf of Mexico again after 3.247 Ma. At the onset of the G20, sea surface temperatures based on TEX86 dropped from 23.2°C to 18.8°C and periods of hyperstratification occurred, although less intense than during M2. | |
