Re‐dating the moraines at skálafellsjökull and heinabergsjökull using different lichenometric methods: implications for the timing of the icelandic little ice age maximum

Abstract

Little Ice Age (LIA) moraines along the margins of Skálafellsjökull and Heinabergsjökull, two neighbouring outlet glaciers flowing from the Vatnajökull ice‐cap, have been re‐dated to test the reliability of different lichenometric approaches. During 2003, 12 000 lichens were measured on 40 moraine fragments at Skálafellsjökull and Heinabergsjökull to provide surface age proxies. The results are revealing. Depending on the chosen method of analysis, Skálafellsjökull either reached its LIA maximum in the early 19th century (population gradient) or the late 19th century (average of five largest lichens), whereas the LIA maximum of Heinabergsjökull occurred by the mid‐19th century (population gradient) or late‐19th century (average of 5 largest lichens). Discrepancies (c. 80 years for Skálafellsjökull and c. 40 years for Heinabergsjökull) suggest that the previously cited AD 1887 LIA maxima for both glaciers should be reassessed. Dates predicted by the lichen population gradient method appear to be the most appropriate, as mounting evidence from other geochronological reconstructions and sea‐ice records throughout Iceland tends to support an earlier LIA glacier maximum (late 18th to mid‐19th century) and probably reflects changes in the North Atlantic Oscillation. These revised chronologies shed further light on the precise timing of the Icelandic LIA glacier maximum, whilst improving our understanding of glacier‐climate interactions in the North Atlantic.

Rock surface micro−roughness, Schmidt hammer rebound and weathering rind thickness within LIA Skálafellsjökull foreland, SE Iceland

“…This may be explained by exfoliation of basaltic surfaces on older moraines (Etienne 2002) leading to smoothening of rock sur− faces (Dąbski and Tittenbrun 2013) or by diversified structure and texture of stud− ied rocks, which is frequently impossible to notice in the field. Therefore, it is in− ferred that the indices used are unsuitable for precise dating of glacial landforms created since the Little Ice Age, and they do not provide additional arguments in the ongoing discussion about timing of LIA maximum in Iceland (Evans et al 1999;Bradwell 2001Bradwell , 2004Dąbski 2002Dąbski , 2007Dąbski , 2010McKinzey et al 2004;McKinzey et al 2005;Bradwell et al 2006;Orwin et al 2008;Chenet et al 2011;Kirkbride and Winkler 2012). Matthews and Owen (2008) working on gneiss boulders within LIA maximum of Storbreen (Norway) found that Schmidt hammer R−values obtained from sur− faces colonized by Lecidea auriculata lichens gradually decreases from the glacier margin to moraines 30-50 years old, supporting the notion of a rapid but relatively short−term proglacial weathering.…”

“…Consecutively, the study aimed to determine the rate of weathering in freshly deglaciated terrains, as it is an important issue in a light of contemporary retreat of mountain glaciers and paraglacial modification of landscapes in alpine and polar regions. Furthermore, there is an on−going discussion about the timing of LIA in southern Iceland (Evans et al 1999;Bradwell 2001Bradwell , 2004Dąbski 2002Dąbski , 2007Dąbski , 2010McKinzey et al 2004;McKinzey et al 2005;Bradwell et al 2006;Orwin et al 2008;Chenet et al , 2011Kirkbride and Winkler 2012), there− fore, developing tools for relative dating of glacial landforms seems an urging ne− cessity. The marginal zone of Skálafellsjökull constitutes a full LIA and recent moraine sequence, similar to that of Fláajökull, allowing easy access to the oldest as well as the youngest parts of moraines.…”

“…However, this was questioned by McKinzey et al (2005) who critically assessed the historical data and concluded that LIA glacier maximum occurred in S Iceland in the late 18 th to early 19 th cen− tury. There are lichenometrical datings of the outermost Skálafellsjökull moraines pointing at the end of the 19 th century (Gordon and Sharp1983;Evans et al 1999), but other date the oldest moraines rather to the mid 19 th century (McKinzey et al 2004;, depending on the lichenometrical technique used, which is also discussed in Orwin et al (2008) andBradwell (2009). Moraines of Skálafellsjökull were in contact with moraines of Heinabergs− jökull and Fláajökull ( Fig.…”

Application of the Handysurf E-35B electronic profilometer for the study of weathering micro-relief in glacier forelands in SE Iceland

“…However, there is some uncertainty about the oldest moraine ridges in S Iceland (Kirkbridge and Dugmore 2001;Bradwell 2001Bradwell , 2004McKinzey et al 2004;Bradwell et al 2006;Chenet et al , 2011Dąb-ski 2010), and the oldest moraines could have been created in the 18 th or even 17 th centuries, or could have been eroded (Kirkbridge and Winkler 2012). The recession rate, as well as the age of test sites, is shown on Text- fig.…”

The Little Ice Age glacier maximum in Iceland and the North Atlantic Oscillation: evidence from Lambatungnajökull, southeast Iceland

“…Finally, most previous studies in Iceland have used the average of the five largest lichens as the best measure of surface age. However, recent lichenometric research has shown that a description of the lichen size-frequency distribution presents a statistically robust and more powerful technique than using the single largest or several largest lichen thalli (Caseldine 1991;Bull & Brandon, 1998;Bradwell 2004a, McKinzey et al 2004Lowell et al 2005).…”