| 1. |
- Davies, Siwan M., et al.
(författare)
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Tracing volcanic events in the NGRIP ice-core and synchronising North Atlantic marine records during the last glacial period
- 2010
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 294, s. 69-79
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Tidskriftsartikel (refereegranskat)abstract
- Abstract Five basaltic tephra horizons have been identified in the NGRIP ice-core during the last glacial period. Geochemical analyses indicate that these tephras are of Icelandic origin with one horizon identified as the Faroe Marine Ash Zone III (FMAZ III) — an important marker horizon in several marine records within the Faroe Islands margin. The FMAZ III is a few millimetres thick and is constrained to 38,122 ± 723 yr b2k (before year AD 2000) according to the Greenland Ice Core Chronology (GICC05). This event falls directly at the thermal peak of Greenland Interstadial 8 (GI-8) and a marine-ice correlation, based on the position of this tephra, suggests a close coupling of the marine and atmospheric systems at this time. The remaining tephras originate from the Eastern Volcanic Zone with the Katla volcanic system pinpointed as the dominant source. These are thought to represent previously unknown volcanic events which add considerably to our knowledge of Icelandic volcanism during this period. Independent ages are assigned to these events and together with major element characterisation, form the backbone of the tephrochronology framework presented here. Despite the identification of these tephras, this study also demonstrates that the sulphate record may not always act as a suitable proxy for the identification of tephra horizons in ice-core records.
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| 2. |
- Jørgensen, Tine, et al.
(författare)
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A comparative study of ancient sedimentary DNA, pollen and macrofossils from permafrost sediments of Northern Siberia reveals long-term vegetational stability
- 2012
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Ingår i: Molecular Ecology. - 0962-1083. ; 21:8, s. 1989-2003
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in Undetermined Although ancient DNA from sediments (sedaDNA) has been used to investigate past ecosystems, the approach has never been directly compared with the traditional methods of pollen and macrofossil analysis. We conducted a comparative survey of 18 ancient permafrost samples spanning the Late Pleistocene (4612.5 thousand years ago), from the Taymyr Peninsula in northern Siberia. The results show that pollen, macrofossils and sedaDNA are complementary rather than overlapping and, in combination, reveal more detailed information on plant palaeocommunities than can be achieved by each individual approach. SedaDNA and macrofossils share greater overlap in plant identifications than with pollen, suggesting that sedaDNA is local in origin. These two proxies also permit identification to lower taxonomic levels than pollen, enabling investigation into temporal changes in species composition and the determination of indicator species to describe environmental changes. Combining data from all three proxies reveals an area continually dominated by a mosaic vegetation of tundra-steppe, pioneer and wet-indicator plants. Such vegetational stability is unexpected, given the severe climate changes taking place in the Northern Hemisphere during this time, with changes in average annual temperatures of >22 degrees C. This may explain the abundance of ice-age mammals such as horse and bison in Taymyr Peninsula during the Pleistocene and why it acted as a refugium for the last mainland woolly mammoth. Our finding reveals the benefits of combining sedaDNA, pollen and macrofossil for palaeovegetational reconstruction and adds to the increasing evidence suggesting large areas of the Northern Hemisphere remained ecologically stable during the Late Pleistocene.
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| 3. |
- Rasmussen, Tine L., et al.
(författare)
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Atlantic surface water inflow to the Nordic seas during the Pleistocene-Holocene transition (mid-late Younger Dryas and Pre-Boreal periods, 12 450-10 000 a BP)
- 2011
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 26:7, s. 723-733
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Tidskriftsartikel (refereegranskat)abstract
- The inflow of Atlantic Water to the Nordic seas from mid-late Younger Dryas to earliest Holocene (12 450-10 000 a BP) is reconstructed on the basis of a high-resolution core (LINK14) from 346 m water depth on the east Faroe shelf. We have analysed the distribution of planktic and benthic foraminifera, stable isotopes and ice-rafted debris (IRD), and calculated absolute temperatures and salinities by transfer functions. During the investigated time period there was almost continuous inflow of Atlantic Water to the Nordic seas. Deposition of IRD during the mid-late Younger Dryas and Pre-Boreal coolings indicates the presence of melting icebergs and that summer sea surface temperatures were low. The east-west temperature gradient across the Faroe-Shetland Channel was much steeper than today. The cold conditions around the Faroe Islands are attributed to stronger East Greenland and East Icelandic currents than at present. The near-continuous inflow of Atlantic Water is consistent with published evidence suggesting that deep convection took place in the Nordic seas, although the convection sites probably had shifted to a more easterly position than at present. Around the time of deposition of the Saksunarvatn Tephra c. 10 350 a BP, sea surface temperatures increased to the present level.
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| 4. |
- Wastegård, Stefan, 1961-, et al.
(författare)
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Faroe Marine Ash Zone IV : a new MIS 3 ash zone on the Faroe Islands margin
- 2014
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Ingår i: Gas Generation and Migration in Deep Geological Radioactive Waste Repositories. - London : The Geological Society Publishing House. - 9781862397132 ; , s. 81-93
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Bokkapitel (refereegranskat)abstract
- A basaltic tephra layer from MIS 3 has been discovered by analysis of cores from the Faroe Islands margin. The tephra layer appears up to 20 cm thick in some records. After the first main fall-out event the tephra is believed to be mainly deposited and redistributed by bottom currents. Geochemical analyses suggest that the tephra is relatively undisturbed by allochtonous tephra grains and unmixed. The peak occurrences are in the lower part of GIS (Greenland Interstadial) 12 and we suggest naming this new tephra Faroe Marine Ash Zone IV (FMAZ IV), following the nomenclature adopted for previous ash zones found on the Faroe Islands margin. Geochemical analyses of the tephra show affinities with the Grimsvotn volcanic system in the Eastern Volcanic Zone in south Iceland. The average age of FMAZ IV from four independent age models is 46 800 +/- 1000 years BP. We suggest that the V5 ash zone, found on the Reykjanes Ridge is a correlative to the FMAZ IV.
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