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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.earscirev.2009.03.005 Byline: John L. Smellie (a), Alan M. Haywood (a)(c), Claus-Dieter Hillenbrand (a), Daniel J. Lunt (a)(b), Paul J. Valdes (b) Keywords: Pliocene; GCM; Antarctic Peninsula Ice Sheet; terrestrial; marine; glaciovolcanic Abstract: In this paper, we examine the nature of the Pliocene Antarctic Peninsula Ice Sheet by comparing the terrestrial and marine geological records of the Antarctic Peninsula and surrounding sea floor with estimated net snow accumulation in the region derived from numerical palaeoclimate model experiments. Pliocene geological data and our new modelling results are consistent and mutually supportive in suggesting that an ice sheet was present even during the warmest episodes of the Pliocene. The combined results suggest that the ice sheet in the Antarctic Peninsula is more robust to globally warmer conditions than is generally assumed, at least up to the climatic limits examined in our study. Author Affiliation: (a) Geological Sciences Division, British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK (b) School of Geographical Sciences, The University of Bristol, University Road, Bristol, BS8 1SS, UK (c) School of Earth & Environment, University of Leeds, Leeds LS2 9JT, UK Article History: Received 28 July 2008; Accepted 20 March 2009

Subglacially-erupted volcanic sequences provide proxies for a unique range of palaeo-ice parameters and they are potentially highly useful archives of palaeoenvironmental information, particularly for pre-Quaternary periods. They can thus be incorporated by climate and ice sheet modellers in the same way as other environmental proxies, yet they remain largely under-utilised. Basaltic volcanic sequences erupted subglacially consist empirically of two major types, corresponding to eruptions under 'thick' and 'thin' ice, respectively. The latter are called subglacial sheet-like sequences and only one genetic type of sequence has been described so far. However, there is now evidence that there are at least two genetic types, with significantly different implications for interpretations of associated palaeo-ice sheet thicknesses. One type, which is relatively well described, is believed to be a diagnostic product of eruptions associated with a relatively thin glacial cover ( 1000 m). Eruptions that form the Dalsheidi-type of sequence commence with the injection and inflation of a sill along the ice: bedrock interface. Such 'interface sills' were predicted theoretically but had no known geological example, until now. Subsequent evolution commonly involves floating of the ice cover, catastrophic meltwater drainage and emplacement of widespread sheets of hyaloclastite, as cohesionless mass flows and hyperconcentrated flows. The water-saturated hyaloclastite is characteristically intruded by apophyses sourced in the underlying 'interface sill'. Eruptions are commonly not explosive until their later stages. Dalsheidi-type deposits are outflow sequences probably linked to subglacial pillow volcanoes, which in Iceland were erupted along fissures. They only provide an indication of minimum thicknesses of the associated overlying ice, although theoretical considerations suggest substantial ice thicknesses in excess of 1000 m. However, they are likely to be characteristic products of eruptions under the thick West Antarctic Ice Sheet, but are currently inaccessible. Such eruptions may be capable of destabilising that ice sheet. Keywords: subglacial eruptions; glaciovolcanic, basaltic; sheet-like; Dalsheidi; Pinafore; ice sheet; palaeoenvironments; West Antarctic Ice Sheet

The northern Antarctic Peninsula region has undergone ~10 m.y. of eruptive activity by basaltic volcanoes, mainly in subglacial settings. Spectacular exposures of lava-fed deltas, capped by basalt flows and commonly underlain by glacigenic sediments on top of a Cretaceous sedimentary 'basement,' characterize James Ross, Vega, and other islands and promontories in the region. Neogene strata are collectively known as the James Ross Island Volcanic Group and record a cryptic history of glaciation, with the timing of events determinable by argon-isotope dating. Focusing especially on the glacigenic sediments themselves, and their relationships with overlying or bounding volcanic rocks, we define facies associations related to (1) eruptions beneath thick ice (>200 m) that produced lava-fed deltas resting on, and intermingling with, diamictite; and (2) eruptions under marine conditions that typically culminated in the development of several tuff-cone successions, some on top of presumably relict glacially striated surfaces. A combination of provenance studies on clasts in the glacigenic sediments, some of which are derived from the Antarctic Peninsula, and geochronology, leads to the conclusion that an Antarctic Peninsula Ice Sheet extended over James Ross and Vega Islands at about the time that the main volcanic edifices began to grow, i.e., prior to ca. 6.2 Ma at least. Much of the subsequent development of the succession is attributed to the interaction between the growing volcanoes and local ice caps. Full resolution of glacial-interglacial events in this region promises to inform the debate about the stability of the most climatically sensitive part of the Antarctic Ice Sheet during the Neogene Period. Keywords: Neogene glacial fluctuations, James Ross Island, Antarctic Peninsula Ice Sheet, glacier-volcano interaction, glacigenic sediments, lava-fed deltas, argon dating, strontium dating.