Jökull - 01.01.2012, Blaðsíða 80

S. Wastegård and J. Boygle
tion of the glass, supported by radiocarbon analyses,
he made correlations with volcanic events described
from Iceland, e.g. Hekla-4 (ca. 4260 BP), Hekla-3 (ca.
3000 BP) and Askja-1875. The pollen stratigraphy
of many sites also aided in the identification of the
tephra horizons. One interesting aspect of Persson’s
work was that the time-transgressive immigration of
spruce (Picea abies) to central Sweden could be fol-
lowed using the Hekla-3 tephra as a time-synchronous
marker (Persson, 1966, p. 391). Later investigations
of some of the sites studied by Persson and other sites
in the vicinity have confirmed many of his findings,
e.g. the tephras mentioned above, but also other events
that were less well-known when Persson did his in-
vestigations, such as the Hekla-S/Kebister tephra (ca.
3720 BP; Boygle, 1998; Wastegård et al., 2008). The
most complete tephrostratigraphy so far is from the
Klocka bog, western central Sweden (Figure 1) where
five tephras have been confirmed (Lairg-A, Hekla-4,
Hekla-S/Kebister, Hekla-3 and Askja-1875; Bergman
et al., 2004). This site and sites further south sug-
gest that the most significant middle to late Holocene
isochrones in Sweden are Hekla-4, Hekla-S/Kebister,
Hekla-3 and Askja-1875 (Boygle, 2004; Wastegård,
2005; Borgmark and Wastegård, 2008). Other tephras
have been identified in single sites and are currently
less valuable as marker horizons, but are potentially
important for the future. One such recent addition
to the tephrochronology of Scandinavia is the Sn-2
Tephra (ca. 3600 BP; Wastegård et al., 2009), found
in the small bog Lilla Backsjömyren (Figure 1). This
part of Sweden is also the only area where a basaltic
tephra has been found, the Veidivötn-AD 1477 layer
reported from a mountain lake, Lake Getvaltjärnen
(Figure 1), close to the border to Norway (Davies et
al., 2007).
Although almost 50 years have passed since the
first records of tephra were made in Swedish peat
records, many parts of Sweden still remain to be
investigated. Recent results from northern Norway
(Pilcher et al., 2005; Vorren et al., 2007; Balas-
cio et al., 2011) suggest that several tephras might
also be found in northern Sweden, especially close
to the border to Norway where precipitation is high.
Southern Sweden is another area where investiga-
tions have been sparse, especially for the middle to
late Holocene. However, records of several tephras
in bogs in northern Germany (van den Bogaard and
Schmincke, 2002) suggest that south Sweden may
also have received tephra from several Icelandic erup-
tions. Increased concentrations of airborne particles
were recorded in pollen monitoring sites in south
Sweden in connection with the recent eruptions of
Eyjafjallajökull and Grímsvötn in 2010 and 2011 re-
spectively (Åslög Dahl and Kerstin Alm Kübler, pers.
comm.). It remains to be seen, however, if tephra from
these eruptions have also been preserved in peat or in
lake sediment sequences.
Distal sites are becoming increasingly important
for obtaining the most comprehensive history of vol-
canic events and for highlighting those events that
have the potential to be used as isochronous marker
horizons. This is especially true for the LGIT where
preservation conditions for Icelandic layers were un-
favorable in the terrestrial environment on Iceland at
that time (Larsen and Eiríksson, 2008).
Acknowledgements
We thank Uni Árting and an anonymous reviewer for
their constructive comments on our manuscript.
ÁGRIP
Sigurður Þórarinsson hefur veitt fjöldamörgum
gjóskulagafræðingum innblástur í tímans rás. Þeg-
ar í doktorsritgerð sinni 1944 benti hann á líkur þess
að finna gjósku úr stórum eldgosum á Íslandi í mó-
mýrum í Skandinavíu. Christer Persson vann braut-
ryðjandastarf í gjóskurannsóknum þar og síðan hafa
yfir 15 gjóskulög fundist í mó og setlögum í Svíþjóð.
Útbreiddasta gjóskan frá lokum síðasta jökulskeiðs
og byrjun nútíma (fyrir 15-9 þúsund árum) er súri
hluti Vedde öskunnar (um 12.100 ára) en hún finnst
á allmörgum stöðum í stöðuvatnaseti og í sjávarleir,
nú á þurru landi vegna landriss, sunnan við jökul-
garða frá Yngra holtasóleyjarstigi. Nýlega fundust
tvö gjóskulög frá þessu tímabili, Håsseldalen gjóskan
(um 11.300 ára) og Askja-S gjóskan (um 10.400 ára),
sem eru mikilvæg viðbót við gjóskulagatímatalið í
norðvestur Evrópu. Mikilvægustu jafntímafletirnir á
mið- og síðari hluta nútíma í Svíþjóð eru gjóskulögin
78 JÖKULL No. 62, 2012