Reconstructing the last Irish Ice Sheet 2: a geomorphologically-driven model of ice sheet growth,retreat and dynamics |
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| Authors: | Sarah L Greenwood Chris D Clark |
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| Institution: | 1. Department of Physical Geography & Quaternary Geology, Stockholm University, 10691 Stockholm, Sweden;2. Department of Geography, University of Sheffield, Winter Street, Sheffield S10 2TN, UK;1. Departments of Arctic Geology and Arctic Geophysics, University Centre in Svalbard, 9170 Longyearbyen, Norway;2. Department of Physical Geography and Quaternary Geology, Stockholm University, 106 91 Stockholm, Sweden;3. Bolin Centre for Climate Research, Stockholm University, 106 91 Stockholm, Sweden;4. Department of Geography and Sustainable Development, University of St Andrews, KY169AL, St Andrews, Scotland, UK;5. School of Geography, Queen Mary University of London, E14NS, London, UK;6. Department of Geography, College of Science, Swansea University, SA2 8PP, UK;1. School of Geography, Queen Mary University of London, Mile End Road, London E1 4NS, UK;2. Department of Geography, University of Portsmouth, Buckingham Building, Lion Terrace, Portsmouth PO1 3HE, UK;1. School of Geography, Queen Mary University of London, Mile End Road, London, E1 4NS, UK;2. Department of Geography, University of Portsmouth, Buckingham Building, Lion Terrace, Portsmouth, PO1 3HE, UK;3. Department of Geology, Lund University, Sölvegatan 12, 223 62, Lund, Sweden;1. British Geological Survey, Murchison House, West Mains Road, Edinburgh EH93LA, UK;2. Department of Geographical and Earth Sciences, University of Glasgow, Glasgow G128QQ, UK;3. Institute of Geography, University of Edinburgh, Drummond Street, Edinburgh EH89XP, UK |
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| Abstract: | The ice sheet that once covered Ireland has a long history of investigation. Much prior work focussed on localised evidence-based reconstructions and ice-marginal dynamics and chronologies, with less attention paid to an ice sheet wide view of the first order properties of the ice sheet: centres of mass, ice divide structure, ice flow geometry and behaviour and changes thereof. In this paper we focus on the latter aspect and use our new, countrywide glacial geomorphological mapping of the Irish landscape (>39 000 landforms), and our analysis of the palaeo-glaciological significance of observed landform assemblages (article Part 1), to build an ice sheet reconstruction yielding these fundamental ice sheet properties. We present a seven stage model of ice sheet evolution, from initiation to demise, in the form of palaeo-geographic maps. An early incursion of ice from Scotland likely coalesced with local ice caps and spread in a south-westerly direction 200 km across Ireland. A semi-independent Irish Ice Sheet was then established during ice sheet growth, with a branching ice divide structure whose main axis migrated up to 140 km from the west coast towards the east. Ice stream systems converging on Donegal Bay in the west and funnelling through the North Channel and Irish Sea Basin in the east emerge as major flow components of the maximum stages of glaciation. Ice cover is reconstructed as extending to the continental shelf break. The Irish Ice Sheet became autonomous (i.e. separate from the British Ice Sheet) during deglaciation and fragmented into multiple ice masses, each decaying towards the west. Final sites of demise were likely over the mountains of Donegal, Leitrim and Connemara. Patterns of growth and decay of the ice sheet are shown to be radically different: asynchronous and asymmetric in both spatial and temporal domains. We implicate collapse of the ice stream system in the North Channel – Irish Sea Basin in driving such asymmetry, since rapid collapse would sever the ties between the British and Irish Ice Sheets and drive flow configuration changes in response. Enhanced calving and flow acceleration in response to rising relative sea level is speculated to have undermined the integrity of the ice stream system, precipitating its collapse and driving the reconstructed pattern of ice sheet evolution. |
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