Fróðskaparrit - 01.01.1998, Page 240

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PALYNOLOGICAL AND VEGETATIONAL CHANGES ASSOCIATED WITH
THE DEPOSITION OF SAKSUNARVATN ASHIN THE FAROE ISLANDS
Fig. 1. Map ofthe Faroe Islands showing sites
mentioned in the text.
Mynd 1. Kort av Føroyum, ið vísir støðini, sum eru
nevnd í tekstinum.
from the palaeolake site of Hoydalar,
Streymoy (Fig. 1) by Waagstein and Jóhan-
sen in 1968 (cf. Jóhansen, 1975). The ash
takes its name from the site of Saksunar-
vatn, Streymoy, from which the Geological
survey of Denmark had extracted a core of
36.75 m depth in water of about 15.0 m in
1972 (Jóhansen, 1978; 1982; 1985). The
basin was not bottomed, but the eponymous
ash formed a 45 cm layer from 29.85-30.30
m.
Published geochemical data on the ash
may be found in a variety of sources (e.g.
Waagstein and Jóhansen, 1966; Mangerud
et al., 1986; Birks et al., 1996). Under the
ordinary light microscope, the tephra ap-
pears predominantly to consist of light
brown glass shards of irregular shape. The
latest age estimates for the ash layer, based
on AMS (accelerator mass spectrometry)
radiocarbon dating of terrestrial plant
macrofossils from Krákenes, westem Nor-
way, is 8930-9060 BP (9930-10,010 cal
BP) (Birks etal., 1996). This range is close
to the original estimates of 9140±160 BP at
Hoydalur (Jóhansen, 1975) and 9000 BP at
Saksunarvatn (Mangerud et al., 1986).
Although a distal tephra (Edwards et ai.
1994), the massive nature of the Saksunar-
vatn ash as found in Faroese deposits,
where it forms visible layers (compared to
the invisible dusting found in Norway),
might be expected to have had an impact
upon local vegetation. Pollen data in direct
association with the Saksunarvatn ash are,
however, rare (but see Rundgren, 1997) and
have been lacking, hitherto, from the
Faroes. The tephra-palynology/vegetation
al relationship is examined here using high
resolution pollen data from new sites on the
Faroese islands of Streymoy and Suðuroy
(Fig. 1).
Previous pollen studies from Faroese
sites containing Saksunarvatn ash
Data are available from three published
current or former lake basin sites - Saksun-
arvatn and Hoydalar on Streymoy and Hovi
A on Suðuroy. Close examination of the
pollen diagrams reveals that with the possi-
ble exception of Hoydalar, the pollen spec-
tra do not have an intimate association with
the ash layer, i.e. they are not located con-
tiguously with, or within, the visible
tephra-laden stratum as depicted on the