Jökull - 01.12.2007, Blaðsíða 23

Reviewed research article
Testing the size-frequency-based lichenometric dating curve on
Fláajökull moraines (SE Iceland) and quantifying lichen
population dynamics with respect to stone surface aspect
Maciej Dąbski
Department of Geomorphology, Faculty of Geography and Regional Studies,
University of Warsaw, Krakowskie Przedmie cie 30, 00-927 Warsaw, Poland
email: mfdbski@uw.edu.pl
Abstract— A recently elaborated lichenometric dating curve for SE Iceland based on an analysis of the size-
frequency 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 mora-
ine 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 fur-
ther light on the use of the size-frequency gradient method and provide information regarding lichen dynamics
dependent on environmental conditions.
Key words: Iceland, lichenometry, Little Ice Age, glacier fluctuation, geomorphology
INTRODUCTION
The lichenometric method was used for the first time
in geomorphological research by Beschel (1950) to
date moraines of 24 different Alpine glaciers. Since
then, the method has been considerably developed
(Locke et al., 1979; Innes, 1982, 1983a, 1983b, 1985;
Caseldine, 1990, 1991; Evans et al., 1999). Benedict
(1967, 1985) first adopted the lichens population ap-
proach and recently Bradwell (2004) obtained a size-
frequency-based dating curve for SE Iceland, which
was tested by McKinzey et al. (2004) for Skála-
fellsjökull and Heinabergsjökull moraines (Figure 1).
These studies discuss in depth differences in the liche-
nometric techniques used previously and reach conc-
lusions that Bradwell’s (2001, 2004) tandem approach
using both “age-size” and “age-gradient” curves toge-
ther yield reliable dates.
The age of Fláajökull moraines (SE Iceland) was
discussed by Jaksch (1975), Snorrason (1984), Dąb-
ski et al. (1998) and in-depth by Dąbski (2002) who
concluded that there is a considerable margin of er-
ror in lichenometric dating due to uncertain growth
rates and unstable environmental conditions. Dąbski
(2002) compared glaciological, cartographical and hi-
storical data with lichenometrical dates based on the
average of the five largest Rhizocarpon agg. thalli, ac-
cording to the method used by Evans et al. (1999) in
dating neighbouring moraines.
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