Last Remnants of Cenozoic Vegetation and Organic-Walled Phytoplankton in the Antarctic Peninsula’ s Icehouse World Sophie Warny Department of Geology and Geophysics and Museum of Natural Science, Louisiana State University Baton Rouge, Louisiana, USA Rosemary Askin Jackson, Wyoming, USA A late Oligocene, a middle Miocene, and two adjacent Pliocene sections were sampled off the coast of the Antarctic Peninsula in shelf sediments on the Joinville Plateau, Weddell Sea. Drilling was conducted from the research vessel icebreaker Nathaniel B. Palmer during the 2006 SHALDRIL cam- paign. The drill holes recovered sediment cores that each span a short interval of time because of extensive sea ice constraints during drilling. Despite this limitation, the palynomorphs extracted from these sediments help constrain the region’ s past environmental conditions during three periods of the “ice- house” world and confirm that tundra vegetation persisted in the Antarctic Peninsula up to at least 12.8 Ma. The terrestrial palynological data reflect southern beech and conifer-dominated woodlands and tundra during the Oligocene, with reduction to pockets of tundra with probably stunted beech and podocarp conifers by the middle Miocene. During both the Oligocene and the Miocene, the phytoplankton were dominated by small sea ice-tolerant opportunistic species taking advantage of the migration of most dinoflagellate cysts to more hospitable parts of the ocean. By the Pliocene, only limited pockets of vegetation may have existed. 1. INTRODUCTION Understanding the timing and characteristics of the evolving post-Eocene Antarctic Ice Sheet is fundamental for constraining the mechanisms driving climate cooling. In turn, this information is needed by modelers quantifying how ice sheet expansion and contraction impacts global climate. The Antarctic Peninsula is located in lower latitudes compared to the rest of the Antarctic Tectonic, Climatic, and Cryospheric Evolution of the Antarctic Peninsula Special Publication 063 Copyright 2011 by the American Geophysical Union. 10.1029/2010SP000996 167