Description: The recent volcanic eruptions of Eyjafjallajökull 2010 and Grímsvötn 2011 demonstrated the risks that mediumsized explosive Icelandic eruptions pose to the North Atlantic region. Using the Eyjafjallajökull 2010 eruption as a case study, we assess how traceable such eruptions are in the marine sedimentary record at medial distances from the source and investigate which factors have affected the particle transport to the marine sedimentary archive. During R/V Poseidon cruise 457, we recovered 13 box cores at 100–1600 m water depths and distances of 18–180 km southwest, south, and east of Iceland. Volcanic glass shards from the uppermost surface sediment were analyzed for their major element composition by electron microprobe and assigned to their eruptive source by geochemical fingerprinting. The predominantly basaltic particles are mostly derived from the Katla, Grímsvötn-Lakagígar, and Bárðarbunga-Veiðivötn volcanic systems. We also identified rhyolitic particles from the Askja 1875 and Öræfajökull 1362 eruptions. Only three out of almost 900 analyzed glass shards are derived from the recent Eyjafjallajökull 2010 eruption, suggesting that medium-sized eruptions are only poorly preserved in marine sediments located at medial distances southwest to east of Iceland. We conclude that the frequency of past medium-sized eruptions is likely higher than detectable in this archive.

Description: Icelandic explosive volcanic eruptions such as the 2010 Eyjafjallajökull eruption have far-reaching impacts. Tephra has been found as far as Northern Continental Europe and Greenland. On Iceland, however, erosion and ice cover limit the preservation, particularly of pre-Holocene volcanic deposits. We use the marine sedimentary archive offshore southeast Iceland, which preserves information about the depositional fans at medial distances from the volcanic sources, to infer past eruption frequencies and geochemical characteristics of the volcanic systems, contributing to Icelandic volcanic hazard assessment and to the stratigraphic framework used for palaeoceanographic reconstructions. Here we report the analysis of four sediment gravity cores of ~5 to 10 m lengths, obtained during RV Poseidon Cruise 457, at distances of 60 to 180 km southeast of Iceland between 755 m and 1610 m water depths. In addition to prominent tephra layers, the inter-core correlation is supported by color-scans and tied in with the δ18O Greenland Ice-core record, providing the age model. We analyzed major element compositions of volcanic glass by electron microprobe. Using geochemical fingerprinting and sedimentary observations, we identified ~50 basaltic primary ash layers. Background sediment includes 〈15% rhyolitic to basaltic-andesitic shards. Although reworking hampers tephrochronological interpretation in the Holocene part of the record, the high abundance of the bimodal Vedde-type tephra implies strong activity of the Katla volcanic system during this time period. Tephras of unknown composition and the “Faroe Marine Ash zones” II and III, including the ~27 ka Fugloyarbanki tephra, provide insight into the Late Pleistocene volcanic activity at the central part of the Icelandic rift zone. The deposits can be traced back 68 ka to the volcanic systems of Grímsvötn-Lakagígar,Kverkfjöll, Bárðarbunga-Veiðivötn, Katla and Hekla. Our results extend their eruption record further back in time than currently inferred from terrestrial Iceland and in more detail than the far-distant records.

Description: Explosive volcanic eruptions on Iceland, even of intermediate magnitude have far-reaching impacts. Their far-distal deposits have been found up to Northern Continental Europe and Greenland. On Iceland, the harsh environment and strongly erosive conditions limit the preservation of volcanic deposits and their accessibility on land. The area offshore southern Iceland preserves information about the depositional fans at medial distance from the volcanic source. Here we use this sedimentary archive to reconstruct the Icelandic eruption record in greater detail. This high resolution geological record allows us to infer eruption frequencies and explosiveness in great detail and contributes to the assessment of Icelandic volcanic hazards, volcano-climate interaction, stratigraphy and palaeoceanographic reconstructions. Eight gravity cores were obtained during RV Poseidon Cruise 457, at 260 to 1,600 m water depths and distances of 130 to 400 km west to southeast of Iceland. The ~4 to 10 m long sediment cores reach back to the Late Pleistocene (~68 ka BP; dated by 14C and sedimentation rates), mostly excluding the Holocene. Potential tephra layers were identified by visual inspection and color scans. Volcanic glass shards were analyzed for their major element composition by electron microprobe and assigned to their eruptive source by geochemical fingerprinting. More than 50 primary tephra layers and nearly as many reworked layers were identified, several of which were correlated across the cores. The mostly basaltic tephra shards are derived from the Katla, Grímsvötn-Lakagígar, Bárðarbunga-Veiðivötn, and Hekla volcanic systems. Primary and mixed layers with particles of unique bimodal composition identical to the ~12 ka BP Vedde-Tephra from the Katla Volcanic System, including rhyolitic particles, were identified in nearly all cores and used as time marker and for inter-core correlation. Tephra layers of unique unknown composition were also identified and stratigraphically assigned across some of the cores. Intercalated dropstones from Heinrich events provide additional age constraints. The core and tephra correlations are supported by color scans, of which the *b-values tie in with the delta18O Greenland Ice-core record. The marine tephrostratigraphy offshore southern Iceland extends the eruption record further back in time than currently inferred from terrestrial Iceland and in more detail than far-distant deposits. It provides depositional evidence for previously unrecognized eruptions and demonstrates that Icelandic volcanoes erupted more often than previously thought. The depositional time frame of the tephra layers in the cores facilitates to integrate climatically-induced variations in sedimentation rates and conditions at the different sites around Iceland with changes in eruption frequency.

Description: Von welchen bekannten Mengen an Rohstoffen im Meer ist momentan die Rede? Wie fällt der Vergleich zum Land aus? Vermuten Experten im Meer überhaupt ein Rohstoffpotential, welches tatsächlich langfristig Alternativen bieten. Ein Überblick zum Stand des Wissens von Rohstoffvorkommen im Meer gibt Dr. Sven Petersen vom GEOMAR im Interview.