Publication Date

April 2019


Suzanne O'Connell


Earth & Environmental Sciences


English (United States)


Over the last 5 million years, the global benthic foraminiferal d18O record shows a ~+1.5‰ shift reflected by colder temperatures and increase ice cover. The Marine Isotope Stage M2 (3.312-3.264 Ma) is a global glaciation event that corresponds to a ~+0.5‰ shift. This 50 thousand year event, associated with a 20 to 60 m sea level drop, precedes Arctic glaciation and is associated with the onset of the glacial-interglacial cycles of the Quaternary. Turnover Pulse D (3.55-3.40 Ma) is an enigmatic Southern Ocean diatom turnover event that correlates with rising temperatures and ice retraction. The focus of this study is to quantify the environmental characteristics of these two major mid-Pliocene events. The samples used in this study are from ODP Site 697 from ~3.6-3.2 Ma. We examined the diatom community of 31 samples for their use as paleoenvironmental proxies. Diatom assemblages through our ~400 kyr sample interval are generally characterized by open ocean related species and record a period of decreasing warmth. Species associated with Cold/ Sea-Ice related conditions comprise only a small percentage of the diatom assemblages, but indicate the presence of icebergs throughout the entire study interval. The high abundance of the warm species S. oestrupii demonstrates that the modern cold conditions attributed to the Weddell Sea are not yet established, even during the MIS M2 glaciation event. Future studies should implement the diatom assemblage data presented here to further constrain the paleo-latitudinal position of the major Antarctic fronts.



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