Jökull - 01.01.2012, Blaðsíða 56

E. R. Guðmundsdóttir et al.
son et al., 2011) and VAST (Larsen et al., 2011, 2012)
where tephrochronology plays an important role. In
addition to serving as a dating tool and fixing points
in geological archives, tephrochronology or tephra
stratigraphy is a key factor in the study of data on
the geochemistry and eruption frequency of volca-
noes and the interrelationships between eruption se-
quences both spatially and temporally (e.g. Thorar-
insson, 1967; Larsen et al., 1998; Shane, 2000, 2005;
Thordarson and Larsen, 2007; Óladóttir et al., 2008,
2011a).
Dr. Sigurður Þórarinsson was a pioneer in tephra
studies and laid the foundation of tephrochronology
in the 1930’s. His focus was on Holocene tephra lay-
ers in terrestrial Iceland. Since the work of Þórarins-
son, substantial research on tephrochronology in Ice-
land as well as in other parts of the world, where
tephra layers exist, has been carried out (Lowe, 2011).
Considerable knowledge on Holocene tephra stratig-
raphy and tephrochronology has been gathered from
terrestrial archives in Iceland especially in the south-
ern, northern and central parts (e.g. Thorarinsson,
1958,1967, 1976; Larsen, 1984, 2000; Larsen et al.,
2001; Óladóttir et al., 2005, 2008, 2011a,b).
With increased research emphasis on climate and
climate change the studies of tephrochronology have
stretched into the marine realm which has enabled re-
liable dating and secure land-sea correlations of vari-
ous climate archives. Knowledge on tephra stratigra-
phy and tephrochronology in the marine realm, espe-
cially in the North Atlantic region, has been continu-
ally increasing (e.g. Kvamme et al., 1989; Sejrup et
al., 1989; Sjøholm et al., 1991; Lacasse et al., 1998;
Eiríksson et al., 2000; Lacasse and Garbe-Schönberg,
2001; Knudsen and Eiríksson, 2002; Andrews et al.,
2002; Rasmussen et al., 2003; Wastegård et al., 2005;
Kristjánsdóttir et al., 2007; Brendryen et al., 2010,
2011; Thornallay et al., 2011; Gudmundsdóttir et al.,
2011a,b, 2012; Davies et al., 2010, 2012).
In this paper we present an overview of the cur-
rent knowledge on Holocene marine tephrochronol-
ogy on the Iceland shelf, (Figure 1 and Table 1). Ma-
rine tephrochronology in the North-Atlantic extends
as far back as 5–6 Ma (Lacasse and Garbe-Schön-
berg, 2001) but the focus here will be on the last
15,000 years. The shelf around Iceland presents a
unique opportunity to study tephrochronology based
on explosive eruptions of volcanoes in Iceland. Dur-
ing the Holocene several hundred tephra layers have
been recorded in terrestrial environments (e.g. Lar-
sen, 2000, 2010; Óladóttir et al., 2005, 2008, 2011a;
Jóhannsdóttir, 2007; Larsen and Eiríksson, 2008a,b;
Thordarson and Höskuldsson, 2008) and over 100
tephra layers in marine archives on the shelf (e.g. An-
drews et al., 2002; Larsen et al., 2002; Eiríksson et al.,
2000, 2002, 2004, 2011; Kristjánsdóttir et al., 2007;
Gudmundsdóttir et al., 2012). The number of Ice-
landic Holocene tephra layers is, however, not com-
pletely known but existing terrestrial records give a
rate of 6.5 tephra layers per century. The estimated
number of postglacial explosive eruptions in Iceland
is close to 2000 (Thordarson and Höskuldsson, 2008).
APPLICATION OF MARINE
TEPHROCHRONOLOGY
Application of marine tephrochronology is mainly
threefold; i) as a tool for dating and correlating differ-
ent environments, ii) for estimating marine reservoir
ages iii) and in volcanology i.e. to gather information
on explosive eruption frequency and history of vol-
canic systems.
Dating and correlation
Tephra studies have become increasingly important
in Quaternary research as tephrochronology is one
of a few techniques that have the potential to ad-
dress chronological uncertainties. In the North At-
lantic region, Greenland and western Europe, Ice-
landic tephra layers have played an important role
in dating and synchronizing different environments
and archives (e.g. Mangerud et al., 1986; Kvamme
et al., 1989; Dugmore et al., 1995a; Turney et al.,
1997; Wastegård et al., 1998; Davies et al., 2001,
2003; van den Bogaard and Schmincke, 2002; Cham-
bers et al., 2004; Pilcher et al., 2005; Wastegård,
2005; Blockley et al., 2007; Wastegård and Davies
2009; Haflidason et al., 2000; Eiríksson et al., 2000a,
2004; Andrews et al., 2002; Knudsen and Eiríks-
son 2002; Larsen et al., 2002; Kristjánsdóttir et al.,
2007; Davies et al., 2010, 2012; Gudmundsdóttir et
54 JÖKULL No. 62, 2012