VSF 2010 Report - Nabo

Chronology
Chronology for the pollen data was provided by AMS radiocarbon dating and a micro-tephra
layer. Two radiocarbon dates were available (Table 1). However SUREC-8391, determined
on charcoal fragments identified as Pinus sylvestris, was rejected as given the absence of
Pinus sylvestris in Iceland this is likely to have been sourced from driftwood or imported
material. Radiocarbon assay SUREC-8386 was determined from Betula charcoal. Birch is
native to Iceland and therefore its charcoal is likely to be of local origin and is considered to
provide a more reliable date for the start of peat accumulation, 890-1020 AD, with a mid
point of 910 AD. In addition to this is a micro-tephra date (recorded 21-23 cm) provided by
Anderson (this report), Katla 1721 AD, was used to provide further chronological control.
Table 1. Radiocarbon dates from base of the wet meadow (Barclay 2008).
Lab
Code
SUREC-
8386
SUREC-
8391
Material
Charcoal
– Betula
Charcoal
– Pinus
sylvestris
14 C
Error ± cal BC/AD 68.2%
Age
Probability
1090 35 895AD (23.6%
)925AD 940AD
(44.6%) 995AD
1060 35 900AD (1.5%)
910AD
970AD (66.7%)
1030AD
cal BC/AD 95.4%
Probability
890AD (95.4%)
1020AD
890AD (95.4%)
1030AD
δ 13 C
-26.7
-24.5
Results
Figure 3 depicts the pollen and spore percentage data for the wet meadow at Vatnsfjörður,
alongside charcoal concentrations. Pollen concentrations of the more dominant land pollen
types are presented in Figure 4. Five local pollen assemblage zones (LPAZ) were constructed
based on local similarities between the communities Vat-1 to Vat-5, providing a means by
which vegetation communities and changes will be described.
The pollen assemblage data suggest that the wet meadow site is predominately a herb
and sedge rich grassland and remains so for the time recorded in this diagram. Throughout
the peat core Poaceae (grasses) dominate each assemblage, dwarf shrubs and herb species
dominate over tree and shrub species, and species diversity would appear to be low. Herb
species are present in much smaller percentages and concentrations. The majority of species
show limited fluctuations between zones.
Fluctuations in charcoal concentrations reflect variations in the smaller sized
fragments (50 µm) are relatively
consistent over time.
LPAZ Vat-1 (c. 910 – 1300 AD)
Poaceae (grasses), although relatively consistent and dominant in percentage values (70-90%)
throughout the zone, demonstrates 2 peaks in concentration firstly at the base of the core c.
910 AD (85%), and then again (90%) at c.1150 AD.
Betula (birch) dominates the tree and shrub classification (10%), with Salix (willow),
appearing in low percentages (