Jökull - 01.01.2012, Blaðsíða 125

Glacier changes in the marginal zone of Sólheimajökull
Table 3. Results of 14C datings from Sólheimajökull. 14C ages were calibrated using the Oxcal v. 4.1.7 soft-
ware with the IntCal04 atmospheric curve (Reimer et al., 2004). – Tafla 3. Niðurstöður aldursákvarðana með
kolefnisgreiningu.
Sample Ångström Locality Easting Northing Altitude Age Calibrated age range Age, Age,
Lab ID (m) (m) (m a.s.l.) (14C BP) (AD, 95.4%±2σ) year AD year BP
SOL0901 Ua-38043 Section 2 580739 7045211 4 m u. surface 449±44 1402–1621 1512 438
SOL0902 Ua-38044 Section 2 580740 7045211 4 m u. surface 377±38 1443–1635 1539 411
Table 4. Results of cosmogenic exposure datings (CED) from Sólheimajökull. – Tafla 4. Niðurstöður aldurs-
ákvarðana með með geimgeislunarmælingum á grettistökum eða berggrunni.
Sample Prime Lab Locality Sample Easting Northing Altitude Age, Error Age,
sample ID type (m) (m) (m a.s.l.) year AD (years) year
(Stone, BP
2000)
SOL-01 200801750 Jökulhaus Bedrock 581831 7045881 252 284 ±513 1666
SOL-02 200801751 Hrossatungur Lateral moraine boulder 582779 7045486 360 858 ±313 1092
SOL-03 200801752 Hrossatungur Lateral moraine boulder 582899 7045606 368 91 ±410 1859
SOL-04 200801753 Hrossatungur Lateral moraine boulder 582849 7045521 360 56 ±606 1894
accumulating early in the LIA, and overridden after
AD 1539, i.e. during the LIA.
Four sites were sampled for CED (Figure 4 and
Table 4). We aimed to date surfaces outside the LIA
glacier extent. One sample was collected from stri-
ated bedrock at the top of Jökulhaus in the central
forefield (Figure 4). It has been debated whether this
small mountain was covered by ice in the LIA or
not (Grove, 2004), and CED might resolve this issue.
Three samples were collected from large boulders on
the prominent lateral moraines southeast of the glacier
(Hrossatungur, Figure 4). This was in order to obtain
an absolute age on the very extensive advance that de-
posited the lateral moraines. Based on tephrochronol-
ogy, Dugmore et al. (2000) concluded that the lateral
moraines were deposited in the 6th–7th century AD.
The rock samples show limited geochemical variabil-
ity and are of evolved FeTi basalt compositions com-
parable to Holocene Katla tephras (Óladóttir et al.,
2008) and segregation veins from Surtsey (Sigmars-
son et al., 2009).
The sample from Jökulhaus (SOL-01; Table 4)
yielded an age of AD 284 which clearly predates the
LIA. Hence, this dating does not support a glacier
advance over the top of Jökulhaus in the LIA. Sam-
ples SOL-02, SOL-03, and SOL-04 from the lateral
moraines yielded ages of AD 858, AD 91, and AD 56,
respectively (Figure 4, Table 4). The age of AD 858
from SOL-02 is an outlier compared to all the other
three samples. On the other hand, SOL-02 agrees
with the moraine ages of 6th–7th century AD from
Dugmore et al. (2000). Based only on the CEDs in
this study, the age determinations could be interpreted
as indicating that the glacier retreated from the lateral
moraines around AD 56–91, i.e. approximately 1.9
kyr BP (Table 4).
Glacier elevation changes 1960–2010
Maps of glacier elevation changes for the period
1960–2010 were produced from the DEMs (Table
1). The elevation change over a given period is de-
rived from the difference between DEMs from two
different years. Figure 9 shows the surface elevation
change between 1960 and 1996 at Sólheimajökull.
The 1960 images are recorded nine years prior to
the 1969 glacier minimum and thus represent a sit-
uation close to this minimum (Figure 2). The 1996
images are recorded only one year after the maximum
glacier extent in 1995 (Figure 2). As a conservative
JÖKULL No. 62, 2012 123