Jökull - 01.12.2007, Side 36

Maciej Dąbski
1. Exceptionally large lichens (Rhizocarpon agg.)
constituting the right outliers of the frequency
distribution graphs should not be used in liche-
nometrical dating based on Bradwell’s (2004)
curve. For the Fláajökull moraines, it appears
sound to exclude all thalli falling to the right of
the first (closest to the modal class) gap of at
least 6 mm on the frequency distribution graph.
The proper age sequence of the moraines is ob-
tained only after such a correction and the li-
chenometric size-frequency-baseddating corre-
sponds relatively well with previous dating ba-
sed on glaciological, cartographical and histori-
cal sources (Dąbski, 2002).
2. The late 19th century maximum of LIA for
Fláajökull is maintained. It is probable that the
three neighbouring southeast outlets of Vatna-
jökull: Skálafellsjökull, Heinabergsjökull and
Fláajökull began retreating from their LIA ma-
ximum positions in a sequence starting from the
early 19th century for the first glacier and en-
ding with the late 19th century for the last gla-
cier.
3. Use of the size-frequency gradient method al-
lows a determination of differences between
the dynamics of lichen population growth de-
pending on the aspect of the stone surface.
This partially answers questions put forward
by Haines-Young (1983) about the ecology of
Rhizocarpon, supports the finding of Pentecost
(1979) and Armstrong (2002) and may prove
useful in further development of lichenometri-
cal studies.
Acknowledgements
The author thanks all students from the Warsaw 99th
Scout Group, Polish Scouting and Guiding Associa-
tion and especially Julia Budziszewska, Jan Kaseja
and Aleksander Tittenbrun for their help in licheno-
metrical measurements and discussion. Linguistic
help from Barbara Przybylska and comments of revie-
wers are kindly appreciated. The work was possible
due to the financial support of the Faculty of Geogra-
phy and Regional Studies, University of Warsaw.
ÁGRIP
Nýlegur mælikvarði yfir vaxtarhraða fléttna á Suð-
austurlandi var reyndur á fléttum á jökulgörðum Fláa-
jökuls. Alls voru 3877 fléttur af gerðinni Rhizocarpon
agg. mældar með tilliti til vaxtarstaðar. Mælingarn-
ar gefa til kynna að hægt sé að nota fléttur minni en
50-100 mm í þvermál til þess að aldursákvarða hop
skriðjökla.
REFERENCES
Ahlmann, H. W. and S. Thorarinsson 1937. Previous in-
vestigations of Vatnajökull, Marginal oscillations of
its outlet-glaciers and general description of its mor-
phology. Geografiska Annaler 19 A, 176–211.
Armstrong, R. A. 2002. The effect of rock surface aspect
on growth, size structure and competition in the lichen
Rhizocarpon geographicum. Environmental and Ex-
perimental Botany 48, 187–194.
Benedict, J. B. 1967. Recent glacial history of an alpine
area in the Colorado Front Range, USA. I. Establish-
ing a lichen growth curve. Journal of Glaciology 6,
817–832.
Benedict, J. B. 1985. Arapaho Pass: glacial geology and
archeology at the crest of the Colorado Front Range.
Ward, Colorado. Center for Mountain Archeology.
Research Report No. 3.
Beschel, R. 1950. Flechten als Altersmassstab rezenter
Moränen. Zeitschrift für Gletscherkunde und Glazial-
geologie 1, 152–161.
Bradwell, T. 2001. A new lichenometric dating curve for
southeast Iceland. Geografiska Annaler 83 A, 91–101.
Bradwell, T. 2004. Lichenometric dating in southeast Ice-
land: the size-frequency approach. Geografiska An-
naler 86 A, 31–41.
Caseldine, C. J. 1990. A review of dating methods and
their application in the development of a chronology
of Holocene glacier variations in northern Iceland. In:
C.J. Caseldine et al., eds. Gletscher und Landschafts-
geschichtliche Untersuchungen im Nordisland. Mün-
chener Geographische Abhandlungen B8, 59–82.
Caseldine, C. J. 1991. Lichenometric dating, lichen popu-
lation studies and Holocene glacial history in Trölla-
skagi, northern Iceland. In K. J. Maizels, C. J. Casel-
dine, eds. Environmental Change in Iceland: Past and
Present. Glaciology and Quaternary Geology. Kluwer
Academic Publishers, Dordrecht, 219–233.
34 JÖKULL No. 57