Fróðskaparrit - 01.01.1998, Side 152

158
HOLOCENE CLIMATIC VARIABILITY IN THE NORTH ATLANTIC REGION
AS SHOWN BY PEAT BOG RECORDS
% transmission
10 15 20 25 30 35 40
Fig. 2. Proxy peat decomposition curve (percentage
transmission) from Migneint, north Wales, UK. An
apparently periodic component is present throughout
the profile.
Mynd 2. Farmynd av niðurbróting av proxytorvi
(leiðing í prosentum) úr Migneint í Wales í Bretlandi.
At síggja til er reglubundið tilfar tvørtur ígjøgnum
allan skurðin.
thresholds) than others. In addition, it
should be noted that different methodolo-
gies were used for data collection and time-
series analysis in all of the studies cited
above.
Solar variability and the peat record
Data from western Ireland (Blackford and
Chambers, 1995) and from the Netherlands
(van Geel, 1996) suggest a link between the
palaeoclimatic record from peat bogs and
solar variability. The link with solar vari-
ability is not a new idea, but comes at a time
of increased interest in solar output varia-
tions in the context of current global warm-
ing (Hoyt and Schatten, 1997). The sugges-
tion is that periods of high atmospheric l4C,
indicative of relatively low solar ‘activity’,
coincide with apparently wetter and or
cooler conditions. This connection is sug-
gested by van Geel (1996) as the mecha-
nism for widespread palaeoenvironmental
and archaeological changes at 2,650 BP.
Other palaeoenvironmental evidence, from
lake levels, tree rings, altitudinal limits of
tree remains, ice core records and cosmo-
genic isotopes combine to show that solar
variability was an important causal compo-
nent of Holocene climatic variability
(Chambers et al., forthcoming). At times,
periodic solar variations may have given
rise to the type of recurrent fluctuations
shown in several published peat-derived
climatic proxies. For example, the Suess
cycle at 210 years may be an explanation,
although with time lags at different places
and for different indicators, of the cycles
inferred by Wijmstra et al. (1984) and
Chambers et al. (1997) as discussed above.
The human impact on mires
One of the fundamental assumptions made
in this field is that the mire surface repre-
sents an environment changing in connec-
tion with climatic parameters. There are
other factors, however, that influence the
rate of growth, vegetation assemblage and
degree of decomposition of mires, and
these could explain an unknown proportion
of the variability shown in individual stud-