Testing the size-frequency-based lichenometric dating curve on Fláajökull moraines (SE Iceland) and quantifying lichen population dynamics with respect to stone surface aspect

Abstract

A recently elaborated lichenometric dating curve for SE Iceland based on an analysis of the sizefrequency gradient has been tested on moraines of Fláajökull, a southeastern outlet glacier from the Vatnajökull ice-cap. The moraines were previously dated based on different sources of information, mostly: glaciological, cartographical and historical. During 2005, 3877 thalli of Rhizocarpon agg. were measured on five moraine ridges deposited since the Little Ice Age maximum. Exceptionally large lichens should not be used for lichenometrical dating of Fláajökull moraines. Instead a method of large thalli reduction has been applied to the moraines. Obtained data correlate relatively well with previous dating of the moraines, and confirm the late 19th century maximum of LIA for Fláajökull. A consistent difference in the size-frequency gradient was observed between lichen populations growing on proximal, distal and upper sides of stones. Our data shed further light on the use of the size-frequency gradient method and provide information regarding lichen dynamics dependent on environmental conditions.

Geomorphic implications of the retreat of Breiðamerkurjökull in the southern part of the Skálabjörg ridge, Esjufjöll, Iceland

“…Lichenometry was applied in order to estimate the timing of the highest lateral moraine ridge deposition. Largest diameters (enveloping circles) of 417 relatively circular thalli of Subgenus Rhizocarpon were measured with use of a plastic ruler (Da ¸bski, 2007). The analysed lichen populations were sampled on proximal, upper and distal surfaces of the moraine ridges shown on Figure 5.…”

Time-dependant surface deterioration of glacially abraded basaltic boulders by Fláajökull, SE Iceland

“…Previous lichenometrical dating of the moraines (Da ¸bski 2002(Da ¸bski , 2007 was carried out along the Hólmsárgarður profile, located along the Hólmsá river and used by the Icelandic Glaciological Society for regular measuring of glacier front fluctuations since 1934 (Sigurðsson, 1998). Lichenometric dates obtained by Da ¸bski (2007), who used the size-frequency approach elaborated by Bradwell (2004) for SE Iceland, correlate relatively well with glaciological measurements (Sigurðsson, 1998), an American map based on aerial photographs taken in 1946 (US Army Map Service, 1949), historical data published by Ahlmann JÖKULL No.…”

“…However, works of Kirkbridge and Dugmore (2001), Bradwell (2001Bradwell ( , 2004, McKinzey et al (2004), Bradwell et al (2006), and based mainly on lichenometry and tephrochronology, conclude that the LIA glacial maxima were reached in SE Iceland at the beginning of 19th century or even at the end of the 18th century. Discrepancies stem from different lichenometrical approaches, uncertainties concerning environmental factors influencing lichen growth rate and possible erosion censoring moraine chronologies (Da ¸bski, 2002(Da ¸bski, , 2007Bradwell, 2009;Armstrong, 2011;Kirkbridge and Winkler, 2012).…”

“…Since the end of the Little Ice Age (LIA), the glacier developed several moraine ridges, dated by Da ¸bski (2002,2007) on the basis of lichenometry as well as historical and cartographical data. Due to an ongoing discussion about the lichenometrically derived age of the oldest moraine and the timing of the LIA Fláajökull maximum, ranging from 1870-1898 AD (Da ¸bski, 2002(Da ¸bski, , 2007(Da ¸bski, , 2010 to 1807-1831 AD (Chenet et al, , 2011, we looked for other age indices of the moraines.…”

“…63, 2013 Figure 1. Location of the Fláajökull marginal zone and the rate of retreat along the Hólmsárgarður profile (Sigurðsson, 1998;Da ¸bski, 2002Da ¸bski, , 2007.…”