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Trimlines separating glacially abraded lower slopes from blockfield-covered summits on Irish mountains have traditionally been interpreted as representing the upper limit of the last ice sheet during the Last Glacial Maximum (LGM). Cosmogenic 10Be exposure ages obtained for samples from glacially deposited perched boulders resting on blockfield debris on the summit area of Slievenamon (721 m a.s.l.) in southern Ireland demonstrate emplacement by the last Irish Ice Sheet (IIS), implying preservation of the blockfield under cold-based ice during the LGM, and supporting the view that trimlines throughout the British Isles represent former englacial thermal regime boundaries between a lower zone of warm-based sliding ice and an upper zone of cold-based ice. The youngest exposure age (22.6±1.1 or 21.0±0.9 ka, depending on the 10Be production rate employed) is statistically indistinguishable from the mean age (23.4±1.2 or 21.8±0.9 ka) obtained for two samples from ice-abraded bedrock at high ground on Blackstairs Mountain, 51 km to the east, and with published cosmogenic 36Cl ages. Collectively, these ages imply (i) early (24-21 ka) thinning of the last IIS and emergence of high ground in SE Ireland; (ii) relatively brief (1-3 ka) glacial occupation of southernmost Ireland during the LGM; (iii) decoupling of the Irish Sea Ice Stream and ice from the Irish midlands within a similar time frame; and (iv) that the southern fringe of Ireland was deglaciated before western and northern Ireland. [ABSTRACT FROM AUTHOR]

Abstract: On the mountains of Western Ireland, the upper limit of glacial evidence descends from 730m in the Connemara Mountains to 400m on Achill Island. This limit is interpreted as a trimline marking the upper limit of erosive, warm-based ice, implying that higher summits remained above a former ice sheet as nunataks or supported a cover of cold-based ice. Significantly greater representation of gibbsite in soils above the trimline indicates that it relates to the last glacial stage. 10Be exposure ages for bedrock samples above the trimline fall within the range (>) 36.0±2.3ka to (>) 61.6±4.0ka, whereas ice-scoured bedrock below the trimline yielded 10Be exposure ages ⩽24.0±1.6ka (and in all but two cases ⩽17.2±1.1ka), consistent with deglaciation after the LGM. Reconstruction of the minimum altitude of the LGM ice surface implies that inland ice was diverted northwestwards by an ice dome on the Connemara Mountains and extended at least 25km offshore. This evidence conflicts with previous accounts that place the LGM ice limit onshore and implies that recent models underestimate LGM ice thickness in Western Ireland. [Copyright &y& Elsevier]

Abstract: Periglacial trimlines on the mountains of SW Ireland demarcate a contrast between glacially scoured bedrock on lower ground and thick periglacial regolith covers on summits and plateaus, and have previously been interpreted as marking the maximum altitude of the Kerry-Cork Ice Cap (KCIC). Glacially eroded bedrock extends to the highest points on the Beara peninsula, but the highest summits on the Iveragh Peninsula support thick regolith covers. Trimline altitudes on the Iveragh Peninsula decline radially from a former ice divide near the head of Kenmare River, from ∼700 m altitude near the divide to ≤470 m near Dingle Bay. Contrasts in the clay mineral content of above- and below-trimline soils and cosmogenic isotope exposure ages indicate a LGM age for the trimlines. Assumption that the trimlines represent the maximum thickness of the KCIC implies an ice divide altitude of ∼825 m. However, modelling of ice-surface profiles demonstrates that an ice divide at 825 m is irreconcilable with stratigraphic evidence for extension of the KCIC at least as far as Garryvoe, 115 km east of the divide. We infer that the Iveragh trimlines represent a former englacial transition between warm-based sliding ice on low ground and cold-based ice on high ground rather than delimiting nunataks as previously interpreted. Modelling of ice-surface altitudes suggests that during the LGM the KCIC probably overtopped all of the mountains in SW Ireland. The trimlines of SW Ireland thus define the minimum rather than maximum altitude of the KCIC at the LGM, as well as the sites of former ‘cold patches’ within the KCIC. [Copyright &y& Elsevier]