Jökull


Jökull - 01.12.1984, Page 58

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
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