Bayesian modelling the retreat of the Irish Sea Ice Stream

Abstract

We present an 8000‐year history spanning 650 km of ice margin retreat for the largest marine‐terminating ice stream draining the former British–Irish Ice Sheet. Bayesian modelling of the geochronological data shows the ISIS expanded 34.0–25.3 ka, accelerating into the Celtic Sea to reach maximum limits 25.3–24.5 ka before a collapse with rapid marginal retreat to the northern Irish Sea Basin (ISB). This retreat was rapid and driven by climatic warming, sea‐level rise, mega‐tidal amplitudes and reactivation of meridional circulation in the North Atlantic. The retreat, though rapid, is uneven, with the stepped retreat pattern possibly a function of the passage of the ice stream between normal and adverse ice bed gradients and changing ice stream geometry. Initially, wide calving margins and adverse slopes encouraged rapid retreat (∼550 m a−1) that slowed (∼100 m a−1) at the topographic constriction and bathymetric high between southern Ireland and Wales before rates increased (∼200 m a−1) across adverse bed slopes and wider and deeper basin configuration in the northern ISB. These data point to the importance of the ice bed slope and lateral extent in predicting the longer‐term (>1000 a) patterns and rates of ice‐marginal retreat during phases of rapid collapse, which has implications for the modelling of projected rapid retreat of present‐day ice streams. Copyright © 2013 John Wiley & Sons, Ltd.

Ice sheet extension to the Celtic Sea shelf edge at the Last Glacial Maximum

“…This compares with evidence from deep-sea cores on the Celtic margin for increases in ice-rafted debris (IRD) of IrishCeltic Sea provenance, with a smaller peak at c. 25.5e24.5 ka BP and a main peak at 23.6e23.4 ka BP encompassing Heinrich Event 2 (HE2; Scourse et al, 2001Scourse et al, , 2009aAuffret et al, 2002). These peaks are consistent with evidence from southern Ireland and the Isles of Scilly for the advance and retreat of the Irish Sea Ice Stream (ISIS) around 25e23 ka ( O Cofaigh and Evans, 2007;O Cofaigh et al, 2012;McCarroll et al 2010;see Chiverrell and Thomas, 2010;Chiverrell et al, 2013). Greenland ice cores record a northward migration of the polar front during this period, suggesting the IRD peaks could correspond to ISIS advance under cold conditions before 24.5 ka BP, followed by retreat under warmer conditions (Scourse et al, 2009a).…”

“…The southernmost extent of the last BritisheIrish Ice Sheet (BIIS) has long been disputed (e.g. Mitchell et al, 1973;Scourse, 1991;Scourse and Furze, 2001;Bowen et al, 2002), but it is now agreed that onshore glacigenic deposits in Ireland and southern Britain provide evidence of an advance of the Irish Sea Ice Stream into the Celtic Sea during the Last Glacial Maximum (LGM), around 25e23 ka BP 1 (Scourse, 1991;Evans, 2001, 2007;Greenwood and Clark, 2009;Chiverrell and Thomas, 2010;Clark et al, 2010;McCarroll et al, 2010;O Cofaigh et al, 2012;Chiverrell et al, 2013). The extent of this advance across the continental shelf has been constrained by a dozen vibrocores acquired in the late 1970s that penetrated surficial sand and gravel to reach sediments of glacial character ( Fig.…”

Sedimentary and structural evolution of a relict subglacial to subaerial drainage system and its hydrogeological implications: an example from Anglesey, north Wales, UK

“…Palaeoenvironmental Reconstruction The glacial sequence exposed at Lleiniog contributes to a wider understanding of the glacial history of the Irish Sea Basin during the Late Weichselian (Devensian) glaciation (Ó Cofaigh & Evans, 2001a;Thomas & Chiverrell, 2007;Evans & Ó Cofaigh, 2008;Scourse et al, 2009;McCarroll et al, 2010;Phillips et al, 2010;Clark et al, 2012a;Chiverrell et al, 2013). Erratic clasts from the basal and upper diamictons (Section 3; Greenly, 1919) are identical to those identified from Lithofacies B (Section 3 -Appendices 1 & 2) and derived from local-and far-travelled bedrock outcrops, and identify common sources for the entire Lleiniog sequence situated within and adjacent to the Irish Sea Basin .…”

Rapid marine deglaciation: asynchronous retreat dynamics between the Irish Sea Ice Stream and terrestrial outlet glaciers

“…It was during this time period that the Irish Sea Ice Stream was advancing through the Irish Sea Basin (Scourse, 1991;McCarroll et al, 2010;Chiverrell et al, 2013), coalescing with the Welsh Ice Cap (Fig. 5a).…”

“…54 H. Patton et al: Rapid marine deglaciation Cofaigh et al, 2012). However, the Irish Sea Basin, host to the largest ice stream of the ice sheet, has received relatively little attention, and inferences on its advance, rapid recession, and interaction with adjacent ice accumulation centres have largely relied on sedimentological interpretations and cosmogenic isotope exposure ages taken from coastal sections (Eyles and McCabe, 1989;Huddart, 1991;Merritt and Auton, 2000;Glasser et al, 2001;Ó Cofaigh and Evans, 2001;Evans and Cofaigh, 2003;Patton and Hambrey, 2009;Van Landeghem et al, 2009;Chiverrell et al, 2013).…”