Jökull - 01.12.1984, Page 58

TAMBORA 1816
LAKI 1783
KOMAGATAKE 1642
U 1602
Fig. 2. High annual aver-
age acidities due to past
volcanic eruptions back to
50 B. C.; Créte core (A)
and Dye 3 core (B). The
annual average acidities
have only been shown, if
the concentration exceeds
approx. 4 pequiv. H+/kg
of ice in at least one of the
two records. The dates
have been obtained by
various stratigraphical
dating methods indepen-
dent of the historic in-
formation on some of the
eruption dates. To the
right is shown the ratio R
= Q/Cz (C) being the
Créte acidity and C2 the
Dye 3 acidity for the same eruptive event). The single Camp Century data at 50 B.C (A) have
added for completeness, Créte: 71°07’N, 37°19’W Camp Century: 77°11’N, 61°09’W.
Mynd 2. Toppar í sýrumagni vegna eldgosa alltfrá 50 f. Kr. í kjarnafrá Créte á Mið-Grœnlandi (A)
Dye 3 á Suður-Grœnlandi.
C1/C2
1816A.D. 1.8
1783 0.7
— 4.7 7.1
1360 (0l1)
1259 2.4
1180 1.3
1107 0.9
931-32 31
_ 3.8
516 A.D.
50 BC 2.3
/U equiv. H+/ kg-yr
been
ogá
have been named. Note, that the data given is the
stratigraphical date for the year of maximum vol-
canic acid concentration, i.e. not necessarily the
year of the eruption.
In Fig. 2 the corresponding high signals in the
Créte core are shown in the same way (larger
than approx. 4 uequiv. H+/kg, from Hammer et
al. (1980 a)). For completeness a single acidity
signal, at 50 B.C., has been added from the
Camp Century core (the “no good core” sign
refer to the Camp Century core). The slight
deviance in the dating of the apparently similar
events in the two records is to be expected, when
considering a dating error of ± 2 years for the
first millennium back in time and ± 4 for the
second millennium.
From a statistical point of view there is little
doubt, that the almost coincident high signals in
the two records represent the same eruptions.
They are: Tambora 1816, Lakagígar 1783,
unknown 1259, Katla 1179?, Hekla 1105, Eldgjá
934-935 and an unknown eruption 50 B.C.
(dates are from Créte core, except the last date).
To the right in the figure are the concentration
ratios R= CfC2 of Créte acidities C] to Dye 3
acidities C2.
In the case of the Hekla eruption it is doubtful,
if exactly the same annual ice layers are com-
pared, because the acid profile over this event is
rather irregular in the Dye 3 core (see evt. Fig.
7): The noisy character of the profile probably
being due to meltlayers etc.
In South Greenland the possibility of a climatic
feedback on the non-volcanic background acidi-
ties cannot be ruled out e.g. periods of warm and
cold summers may introduce corresponding high
and low acidities of the summer snow. This is not
too serious, when comparing strong volcanic sig-
nals, but it will complicate the distinction
between acidity changes caused by volcanic acti-
vity and those caused by climatic feedback
mechanisms.
The high acidity signals in the Créte core in
1642, 1602 and 623 are more obscure, as they
could not be identified in the Dye 3 core except
by depicting the annual layers 1642,1602 and 623
by dating. In a comparison between the Dye 3
core and the Créte core it is therefore uncertain,
56 JÖKULL 34. ÁR