Younger Dryas glaciers and climate in the Mourne Mountains, Northern Ireland

Abstract

Here, we present evidence to suggest that the Mourne Mountains, Northern Ireland, were last occupied by glaciers during the Younger Dryas Stadial. The margins of these glaciers are marked by moraines, chronologically constrained to the Younger Dryas by Schmidt hammer exposure dating. Reconstructions indicate that these glaciers had equilibrium‐line altitudes (ELAs) ranging from 356 ± 33 m (a.s.l.) to 570 ± 9 m (a.s.l.), with a mean of 475 ± 36 m (a.s.l.). ELAs rise from west to east, probably reflecting the contribution of windblown snow and ice to the accumulation of Younger Dryas glaciers in the western Mournes. Taking this into consideration, a mean ‘climatic’ ELA of 529 ± 4 m (a.s.l.) is calculated for the mountains as a whole. Assuming a mean annual sea level air temperature of −8 °C, and an annual temperature range of 34 °C, degree‐day modelling suggests that during the Younger Dryas, accumulation at the ‘climatic’ ELA of glaciers in the Mournes was 846–990 mm a−1. This suggests increased aridity, relative to present, and is consistent with other parts of NW Europe, where reduced precipitation alongside notable cooling is thought to reflect increased North Atlantic sea ice extent during the Younger Dryas.

Timing of glacial retreat in the Wicklow Mountains, Ireland, conditioned by glacier size and topography

“…To develop a deglacial chronology, sampling was focused on prominent moraines and boulder accumulations as these are the best geomorphological indicators of the dimensions of former mountain glaciers (Barr et al ., ). Key sites along the main SW–NE axis of the mountain range were targeted for SH exposure dating (SHED; Tomkins et al , ) including glacially deposited boulders on prominent cirque moraines (>400 m) at Kelly's Lough (KL), Lough Nahanagan (LN), Mullaghcleevaun (MC) and Upper Lough Bray (ULB).…”

“…; Table ). Twenty surfaces were sampled at each site (Carrawaystick Brook; n = 10) and 170 surfaces were sampled in total, comparable to previous applications of SHED in the Mourne Mountains, Northern Ireland (Barr et al ., ).…”

“…(), which includes 10 Be‐dated surfaces from Blackstairs Mountain, Wexford ( n = 2; Ballantyne and Stone, ), and Bloody Foreland, Donegal ( n = 6; Ballantyne et al ., ; Clark et al ., ). These data fit the trend established at calibration sites in Scotland and north‐west England and indicate that errors in SH exposure age estimates due to climatic variability appear unlikely (Barr et al ., ). Calibration site exposure ages are calculated using the online calculators formerly known as the CRONUS‐Earth online calculator (http://hess.ess.washington.edu/math/, Wrapper script 2.3, Main calculator 2.1, constants 2.3, muons 1.1; Balco et al ., ) and are based on the time‐dependent Lm scaling (Lal, ; Stone, ), the Loch Lomond production rate (LLPR; Fabel et al ., ; 4.02 ± 0.18 atoms g −1 a −1 ) and assuming 0 mm ka −1 erosion.…”

Deglaciation chronology of the Donegal Ice Centre, north‐west Ireland

“…Ballantyne and O Cofaigh, 2017), suggesting that these and possibly other mountains in north-west Ireland supported the last remnants of the last Irish Ice Sheet before complete disappearance of glacier ice under the warmer conditions of the Lateglacial Interstadial. The Blue Stack Mountains, along with other mountain areas in Ireland, hosted glaciers during the Younger Dryas Stadial ($12.9-11.7 ka) (Barr et al, 2017;Barth et al, 2018;Tomkins et al, 2018), but it has not yet been demonstrated that these glaciers had persisted throughout the Lateglacial Interstadial.…”

Glacial geomorphology of the Gaick, Central Grampians, Scotland

“…In the case of discrete ice masses (corrie glaciers, valley glaciers and icefields) relating to the Younger Dryas (∼12.9-11.7 ka), geomorphological mapping has facilitated three-dimensional palaeoglaciological reconstructions and, in turn, calculations of palaeoclimatic variables (e.g. Ballantyne, 2002aBallantyne, , 2007aBallantyne, , 2007bBarr, Roberson, Flood, & Dortch, 2017;Bendle & Glasser, 2012;Benn & Ballantyne, 2005;Boston, Lukas, & Carr, 2015;Finlayson, Golledge, Bradwell, & Fabel, 2011;Lukas & Bradwell, 2010). Despite this large body of research, there remain several areas in Britain and Ireland where past glacial events remain poorly constrained, in large part due to the paucity of detailed geomorphological mapping in those areas.…”