Jökull - 01.12.1999, Page 10

Tephra analysis
Tephrochronology was supplementary to radiocar-
bon dating in the construction of absolute chronolo-
gies, and the tephras also facilitated correlations be-
tween the five lake successions. All potential tephra
horizons that were recorded on X-ray photographs or
during visual inspection of the cores were subsampled
for tephrostratigraphical analyses. Segments of these
potential tephra horizons were suspended in water and
washed through 125 pm and 63 pm sieves. After di-
gestion of organic material with H202, the remaining
glass shards were subjected to chemical analysis. Both
a standard wavelength dispersal (EMP) technique and
a scanning electron microscope connected to an ener-
gy dispersive spectrometer (SEM) was used.
RESULTS
In this section, the results presented by Rundgren
(1995), Rundgren et al. (1997), Björck et al. (1997),
Ingólfsson et al. (1997), Rundgren (1998) and Rund-
gren and Ingólfsson (1999) are compiled to form a
synthesis of the environmental history of northern-
most Skagi during the Late Weichselian and Early
Holocene. This period is divided into seven episodes
for which the evidence of terrestrial and limnic vege-
tation, climatic conditions and relative sea level are
discussed separately. A summary of the environmen-
tal changes during the period 11,300-7800 BP on
northernmost Skagi is presented in Fig. 5, together
with proposed correlations to the conventional cli-
matostratigraphy of northwestem Europe.
11,300-10,900 BP
The oldest recorded lake sediments were found in
Lake Torfadalsvatn and Lake Hraunsvatn, and they
belong to regional pollen assemblage zone (RPAZ)
Skagi-1 (Rundgren et al., 1997; Fig. 5). The palyno-
logical results presented by Rundgren (1995) and
Rundgren et al. (1997) suggest that northernmost
Skagi was characterized by grass tundra with a rela-
tively diverse herb component during the period
11,300-10,900 BP, and plant cover was probably
sparse. The pollen record from RPAZ Skagi-1 in-
cludes, for example, Chenopodiaceae, Capsella bursa-
pastoris type, Caryophyllaceae, Oxyria + Rumex and
Saxifraga. Also sedges were important in this early
phase. Relatively high percentage values for Chenopo-
diaceae may reflect proximity to the sea-shore. This is
in accordance with the sea-level reconstruction (Rund-
gren et al., 1997), which shows that Lake Torfadals-
vatn was isolated prior to 11,300 BP and Lake
Hraunsvatn shortly before 10,900 BP (Fig. 6). Both
the terrestrial vegetation and the limnic data (low Pe-
diastrum concentration values and organic carbon
content) indicate a cold climate on northemmost Skagi
between 11,300 and 10,900 BP.
Age (’-C yr BP) Age (calendar yr BP) Reglonal pollen assem- blage zones Dominant vege- tation Lake produc- tivity Climatic ditions Relative sea level Climato- strati- graphy
7800 - 8000 - 8800 - 9600 - 9900 - 10,600 - 10,900 - 11,300 -
not defined shrub and dwarf-s. tundra very high mild unknown Atlantic
not deflned dwarf- shrub and shoib tundra hlgh/ very high mild unknown Boreal
: Skagi-5 dwarf- shrub tundra very hlgh mild falling Pre- boreal
- Skagi-4 herb tundra high- moderate- high cool- cold- cool falling- rising- falling
PBO

: Skagi-3 grass tundra low cold rising- falling Younger Dryas
Skagi-2 dwarf-s. tundra hlgh mild failing Allerod
12,800 - Skagi-1 low cold falllng
12,950 _
Fig. 5. Summary of the development of terrestrial and limnic
environments and relative sea level on northernmost Skagi in
the period 11,300-7800 BP presented on a linear calendar-year
time scale, together with inferred climatic conditions and cor-
relations to the northwestem European climatostratigraphy.
The seven recorded events were related to calendar years BP
(A.D. 1950) using the synchronization of Björck etal. (1996).
- Samantekt á umhverfis-, veðurfars- og sjávarstöðubreyt-
ingum nyrst á Skaga á tímabilinu 11.300-7800 almanaksárum
BP og tenging breytinganna við veðurfarsgögnfrá norðvestur
Evrópu. Hin sjö tímabil eru tengd almanaksárum BP (A.D.
1950) með samanburði við Björck o. fl. (1996).
8
JÖKULL, No. 47, 1999