An exceptional triple palynological signal (unusually high abundance of marine, freshwater,\ud and terrestrial palynomorphs) recovered from a core collected during the 2007 ANDRILL\ud (Antarctic geologic drilling program) campaign in the Ross Sea, Antarctica, provides constraints\ud for the Middle Miocene Climatic Optimum. Compared to elsewhere in the core, this\ud signal comprises a 2000-fold increase in two species of dinofl agellate cysts, a synchronous fi vefold\ud increase in freshwater algae, and up to an 80-fold increase in terrestrial pollen, including\ud a proliferation of woody plants. Together, these shifts in the palynological assemblages\ud ca. 15.7 Ma ago represent a relatively short period of time during which Antarctica became\ud abruptly much warmer. Land temperatures reached 10 C (January mean), estimated annual\ud sea-surface temperatures ranged from 0 to 11.5 C, and increased freshwater input lowered\ud the salinity during a short period of sea-ice reduction

The Antarctic Peninsula is considered to be the last region of Antarctica to have been fully glaciated as a result of Cenozoic climatic cooling. As such, it was likely the last refugium for plants and animals that had inhabited the continent since it separated from the Gondwana supercontinent. Drill cores and seismic data acquired during two cruises (SHALDRIL I and II) in the northernmost Peninsula region yield a record that, when combined with existing data, indicates progressive cooling and associated changes in terrestrial vegetation over the course of the past 37 million years. Mountain glaciation began in the latest Eocene (approximately 37–34 Ma), contemporaneous with glaciation elsewhere on the continent and a reduction in atmospheric CO 2 concentrations. This climate cooling was accompanied by a decrease in diversity of the angiosperm-dominated vegetation that inhabited the northern peninsula during the Eocene. A mosaic of southern beech and conifer-dominated woodlands and tundra continued to occupy the region during the Oligocene (approximately 34–23 Ma). By the middle Miocene (approximately 16–11.6 Ma), localized pockets of limited tundra still existed at least until 12.8 Ma. The transition from temperate, alpine glaciation to a dynamic, polythermal ice sheet took place during the middle Miocene. The northernmost Peninsula was overridden by an ice sheet in the early Pliocene (approximately 5.3–3.6 Ma). The long cooling history of the peninsula is consistent with the extended timescales of tectonic evolution of the Antarctic margin, involving the opening of ocean passageways and associated establishment of circumpolar circulation.

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The Permian-Triassic boundary occurs within a relatively complete terrestrial sequence in the Shackleton Glacier area of the central Transantarctic Mountains. The boundary is within a 7-to 10-m-thick interval between the Permian Glossopteris fl ora and the Lower Triassic Lystrosaurus fauna. This interval, representing on the order of 200 k.y., records some of the events that occurred in the transition from the Permian to Triassic. In the best-documented section at Graphite Peak in the Beardmore Glacier region, Protohaploxypinus microcorpus zone palynomorphs, which we assign to the latest Permian, record the declining Glossopteris fl ora and occur near the top of the Buckley coal measures, just below a previously reported major negative δ 13 C excursion. In the Shackleton Glacier area, the Per mian Glossopteris fl ora, including fossil wood, roots, and leaves, occurs within the lower part of the Fremouw Formation. The Antarctic Lystrosaurus assemblage of Early Triassic age has several species in common with the South African fauna that lived 20° to 35° closer to the equator. The migration of vertebrates from southern Africa into Antarctica in the Early Triassic supports hypotheses of runaway greenhouse warming possibly related to CO 2 emissions from Siberian fl ood basalts and large methane gas releases. Changes in fl ora bracketing the fi rst of the major negative δ 13 C anomalies near the boundary in Antarctica and in East Greenland support the hypothesis that a global event, perhaps through mutations caused by enhanced ultraviolet radiation, may have played a role in the destruction of fl oras.

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Figure 1. Carboniferous and Permian paleogeographic map of Gondwana (after Powell and Li, 1994), showing several hypothetical ice sheets. ABSTRACTEvidence from Antarctica indicates that a 2000-km-long section of the Transantarctic Mountains-including Victoria Land, the Darwin Glacier region, and the central Transantarctic Mountains-was not located near the center of an enormous Carboniferous to Early Permian ice sheet, as depicted in many paleogeographic reconstructions. Weathering profiles and soft-sediment deformation immediately below the preglacial (pre-Permian) unconformity suggest an absence of ice cover during the Carboniferous; otherwise, multiple glacial cycles would have destroyed these features. The occurrence of glaciotectonite, massive and stratified diamictite, thrust sheets, sandstones containing dewatering structures, and lonestone-bearing shales in southern Victoria Land and the Darwin Glacier region indicate that Permian sedimentation occurred in ice-marginal, periglacial, and/or glaciomarine settings. No evidence was found that indicates the Transantarctic Mountains were near a glacial spreading center during the late Paleozoic. Although these findings do not negate Carboniferous glaciation in Antarctica, they do indicate that Gondwanan glaciation was less widespread, and, therefore, that glacially driven changes to other Earth systems (i.e., glacioeustatic fluctuations, climate) were much smaller than previously hypothesized.