EVIDENCE OF THE ELDGJA (ICELAND) ERUPTION IN THE GISP2 GREENLAND ICE CORE - RELATIONSHIP TO ERUPTION PROCESSES AND CLIMATIC CONDITIONS IN THE 10TH-CENTURY

Glaciochemical studies and the evaluation of tephra in the GISP2 ice c ore provide information on the characteristics and potential environme ntal and climatic effects of the mid- to late AD 930s voluminous fissu re eruption of Eldgja, Iceland. The similarity in the chemical composi tion of basaltic glass shards found in a section of core dated at AD 9 38 +/- 4 compared to proximal glass from the Eldgja eruption verifies the presence of Eldgja debris. A dacitic glass present in the same lay er probably originated from Eldgja as well, in which case Eldgja was t he primary contributor of sulphur-rich aerosols to the atmosphere in t he late AD 930s. We cannot completely exclude the possibility that ano ther explosive eruption in the AD 930s produced this dacitic glass. Es timated maximum stratospheric loading is 100 x 10(12) g H2SO4 over a 3 -6 year period following the eruption, but loading could be as low as half of that value. A search of historical and proxy records for the l ate AD 930s to early 940s fail to show a consistent period of climatic cooling, especially considering the lack of an absolute date for the Eldgja eruption. This inconsistent response is similar to that observe d after the equally voluminous AD 1783 fissure eruption of Laki, Icela nd, using the same proxy data sets. However, a marked drop in surface temperatures in the Northern Hemisphere follows the Laki eruption.