Tephra in marine sediment cores offshore southern Iceland: A 68,000 year record of explosive volcanism.

Bonanati, Christina, Wehrmann, Heidi, Portnyagin, Maxim , Hoernle, Kaj , Mirzaloo, Maryam and Nürnberg, Dirk (2016) Tephra in marine sediment cores offshore southern Iceland: A 68,000 year record of explosive volcanism. [Poster] In: EGU General Assembly 2016. , 17.-22.04.2016, Vienna, Austria .

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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.

Document Type: Conference or Workshop Item (Poster)
Additional Information: submitted - EGU2016-16724
Keywords: Tephra, marine sediments, volcanism, Iceland, RV Poseidon, POS457
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS
Date Deposited: 14 Jan 2016 12:44
Last Modified: 08 Mar 2016 07:45
URI: http://oceanrep.geomar.de/id/eprint/30982

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