| 1. |
- Beaudon, Emilie, et al.
(författare)
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Spatial and temporal variability of net accumulation from shallow cores from Vestfonna ice cap (Nordaustlandet, Svalbard)
- 2011
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 93:4, s. 287-299
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Tidskriftsartikel (refereegranskat)abstract
- We analyse ice cores from Vestfonna ice cap (Nordaustlandet, Svalbard). Oxygen isotopic measurements were made on three firn cores (6.0, 11.0 and 15.5 m deep) from the two highest summits of the glacier located on the SW–NE and NW–SE central ridges. Sub-annual δ18O cycles were preserved and could be counted visually in the uppermost parts of the cores, but deeper layers were affected by post-depositional smoothing. A pronounced δ18O minimum was found near the bottom of the three cores. We consider candidates for this δ18O signal to be a valuable reference horizon since it is also seen elsewhere in Nordaustlandet. We attribute it to isotopically depleted snow precipitation, which NCEP/NCAR reanalysis shows was unusual for Vestfonna, and came from northerly air during the cold winter of 1994/95. Finding the 1994/95 time marker allows establishment of a precise depth/age scale for the three cores. The derived annual accumulation rates indirectly fill a geographical gap in mass balance measurements and thus provide information on spatial and temporal variability of precipitation over the glacier for the period spanned by the cores (1992–2009). Comparing records at the two locations also reveals that the snow net accumulation at the easternmost part of Vestfonna was only half of that in the western part over the last 17 years.
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| 2. |
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| 3. |
- Bowman, Chelsie N., et al.
(författare)
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Linking the progressive expansion of reducing conditions to a stepwise mass extinction event in the late Silurian oceans
- 2019
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Ingår i: Geology. - 0091-7613. ; 47:10, s. 968-972
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Tidskriftsartikel (refereegranskat)abstract
- The late Ludlow Lau Event was a severe biotic crisis in the Silurian, characterized by resurgent microbial facies and faunal turnover rates otherwise only documented during the "big five" mass extinctions. This asynchronous late Silurian marine extinction event preceded an associated positive carbon isotope excursion (CIE), the Lau CIE, although a mechanism for this temporal offset remains poorly constrained. Here, we report thallium isotope data from locally reducing late Ludlow strata within the Baltic Basin to document the earliest onset of global marine deoxygenation. The initial expansion of anoxia coincided with the onset of the extinction and therefore preceded the Lau CIE. Additionally, sulfur isotope data record a large positive excursion parallel to the Lau CIE, interpreted to indicate an increase in pyrite burial associated with the widely documented CIE. This suggests a possible global expansion of euxinia (anoxic and sulfidic water column) following deoxygenation. These data are the most direct proxy evidence of paleoredox conditions linking the known extinction to the Lau CIE through the progressive expansion of anoxia, and most likely euxinia, across portions of the late Silurian oceans.
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| 4. |
- Cramer, Bradley D., et al.
(författare)
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Testing the limits of Paleozoic chronostratigraphic correlation via high-resolution (<500 k.y.) integrated conodont, graptolite, and carbon isotope (delta C-13(carb)) biochemostratigraphy across the Llandovery-Wenlock (Silurian) boundary: Is a unified Phanerozoic time scale achievable?
- 2010
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Ingår i: Geological Society of America Bulletin. - 0016-7606. ; 122:9-10, s. 1700-1716
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Tidskriftsartikel (refereegranskat)abstract
- The resolution and fidelity of global chronostratigraphic correlation are direct functions of the time period under consideration. By virtue of deep-ocean cores and astrochronology, the Cenozoic and Mesozoic time scales carry error bars of a few thousand years (k.y.) to a few hundred k. y. In contrast, most of the Paleozoic time scale carries error bars of plus or minus a few million years (m. y.), and chronostratigraphic control better than +/- 1 m. y. is considered "high resolution." The general lack of Paleozoic abyssal sediments and paucity of orbitally tuned Paleozoic data series combined with the relative incompleteness of the Paleozoic stratigraphic record have proven historically to be such an obstacle to intercontinental chronostratigraphic correlation that resolving the Paleozoic time scale to the level achieved during the Mesozoic and Cenozoic was viewed as impractical, impossible, or both. Here, we utilize integrated graptolite, conodont, and carbonate carbon isotope (delta C-13 carb) data from three paleocontinents (Baltica, Avalonia, and Laurentia) to demonstrate chronostratigraphic control for upper Llandovery through middle Wenlock (TelychianSheinwoodian, similar to 436-426 Ma) strata with a resolution of a few hundred k.y. The interval surrounding the base of the Wenlock Series can now be correlated globally with precision approaching 100 k.y., but some intervals (e. g., uppermost Telychian and upper Shein-woodian) are either yet to be studied in sufficient detail or do not show sufficient biologic speciation and/or extinction or carbon isotopic features to delineate such small time slices. Although producing such resolution during the Paleozoic presents an array of challenges unique to the era, we have begun to demonstrate that erecting a Paleozoic time scale comparable to that of younger eras is achievable.
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| 5. |
- Divine, Dmitri, et al.
(författare)
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Thousand years of winter surface air temperature variations in Svalbard and northern Norway reconstructed from ice-core data
- 2011
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Ingår i: Polar Research. - : Norwegian Polar Institute. - 0800-0395 .- 1751-8369. ; 30, s. 7379-
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Tidskriftsartikel (refereegranskat)abstract
- Two isotopic ice core records from western Svalbard are calibrated to reconstruct more than 1000 years of past winter surface air temperature variations in Longyearbyen, Svalbard, and Vardo, northern Norway. Analysis of the derived reconstructions suggests that the climate evolution of the last millennium in these study areas comprises three major sub-periods. The cooling stage in Svalbard (ca. 800-1800) is characterized by a progressive winter cooling of approximately 0.9 degrees C century(-1) (0.38 degrees C century(-1) for Vardo) and a lack of distinct signs of abrupt climate transitions. This makes it difficult to associate the onset of the Little Ice Age in Svalbard with any particular time period. During the 1800s, which according to our results was the coldest century in Svalbard, the winter cooling associated with the Little Ice Age was on the order of 4 degrees C (1.3 degrees C for Vardo) compared to the 1900s. The rapid warming that commenced at the beginning of the 20th century was accompanied by a parallel decline in sea-ice extent in the study area. However, both the reconstructed winter temperatures as well as indirect indicators of summer temperatures suggest the Medieval period before the 1200s was at least as warm as at the end of the 1990s in Svalbard.
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| 6. |
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| 7. |
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| 8. |
- Ebbestad, Jan Ove R., et al.
(författare)
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Terminal Ordovician stratigraphy of the Siljan district, Sweden
- 2015
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 137:1, s. 36-56
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Forskningsöversikt (refereegranskat)abstract
- Integration of new isotopic data and earlier biostratigraphic information from eight sections through the terminal Ordovician (Pirgu and Porkuni stages) of the Siljan district, Sweden, allows a more precise correlation of sections in terms of biostratigraphy and carbon isotope dating. Four levels with positive delta C-13 excursions are identified (from bottom) - the Moe, an unnamed excursion, Paroveja and Hirnantian Carbon Isotope Excursion (HICE). The delta C-13 values through the Boda Limestone are 1-2 parts per thousand higher than usual in Baltica, only the values for the HICE remains within what is expected. Background values increase from 1.5 parts per thousand in the bottom of the core of the Boda Limestone up to 3 parts per thousand in the top of it. The HICE is identified in five of eight sections and the main peak falls according to inferred correlation within the Metabolograptus persculptus Biozone, at or close to the Hindella beds in the Upper Boda Member. The late Katian (Pirgu) age of Holorhynchus in the Siljan district is clear and its co-occurrence with the chitinozoan Belonechitina gamachiana in Estonia supports a Katian age for this zone. The base of the Ozarkodina hassi Biozone may occur within units B-C of the Upper Boda Member and in the upper part of the Loka Formation and most likely is correlated with the M. persculptus Biozone. The Hirnantia-Dalmanitina faunas reported from the lowermost part of the Loka Formation and units B-D of the Upper Boda Member seem to range through all the Hirnantian, but detailed morphological studies allow to distinguish an older (=extraordinarius) and a younger (=persculptus) fauna.
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| 9. |
- Ebbestad, Jan Ove R., 1967-, et al.
(författare)
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Upper Ordovician carbon isotope records in the Siljan district, Sweden
- 2009
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Ingår i: <em>Absolutely final meeting of IGCP 503: Ordovician palaeogeography and palaeoclimate - Copenhagen 2009 - August 31 – September 4</em>. - Copenhagen : Geological Museum, Natural History Museums. ; , s. 23-24
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Upper Ordovician Boda Limestone and the unconformably overlying Glisstjärn Formation in the Siljan district, Sweden, were sampled for carbon isotope analysis. The aim is to combine chemo- andAbsolutely final meeting of IGCP 503: Ordovician palaeogeography and palaeoclimate - Copenhagen 2009 - August 31 – September 424biostratigraphy for detailed regional correlation. This may help further studies of the time interval spanning the two-phased end Ordovician extinction. Expanding upon the study by Schmitz & Bergström (2007), five quarries, eight sections (669 samples) were studied; two sections each in Kallholn, Osmundsberget, and Solberga, and one section each in Östbjörka and Jutjärn. The Glisstjärn Formation is exposed only in one section at Kallholn, both sections at Osmundsberget, and possibly at one section in Solberga. A cephalopod event bed is recognized in one section in Kallholn and the two sections in Osmundsberget. Additionally, a thick coquina consisting of the brachiopod Hindella is found in all quarries except Solberga. The Hirnantian Isotope Carbon Excursion (HICE) was positively identified in seven of the eight sections. The peak occurs at the Hindella bed in all sections. The beginning of the excursion in Osmundsberget is placed slightly higher than in the previous study, at about 14 m from the top of the Boda Limestone, which means it is above the level with the brachiopod Holorhynchus (identified both in Osmundsberget and Solberga). In Osmundsberget, Östbjörka and Jutjärn, sampling of the deeper parts of the Boda Limestone yielded δ13C values between + 1 and + 3 ‰, with two or three peaks higher than + 3 ‰, that may be correlated between the sections
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| 10. |
- Isaksson, Elisabeth, et al.
(författare)
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Climate oscillations as recorded in Svalbard ice core δ 18O records between 1200-1997 AD
- 2005
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Ingår i: Geografiska Annaler. Series A, Physical Geography. - : Informa UK Limited. - 0435-3676 .- 1468-0459. ; 87a:1, s. 203-214
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Tidskriftsartikel (refereegranskat)abstract
- We apply two different time series analytical tools to omega18O records from two Svalbard ice cores. One ice core is from Lomonosovfonna at 1250 ma.s.l. and the other from Austfonna at 750 m a.s.l. These cores are estimated to cover at least the past 800 years and have been dated using a combination of known reference horizons and glacial modelling. Wavelet analysis reveals low frequency oscillations on the 60-120-year scale on the lower elevation site Austfonna while the higher altitude site on Lomonosovfonna does not reveal such variability throughout the record. The second method, Significant Zero Crossing of Derivates (SiZer) does not resolve the low-frequency periodicity seen in the wavelet analysis. The low-frequency variability resolved by the wavelet analysis is similar to what has been found in various climate records including instrumental temperatures and tree-rings, and has been proposed as the most important oscillation for the observed trends in Arctic air temperatures.
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| 11. |
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| 12. |
- Ruppel, Meri M., et al.
(författare)
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Do contemporary (1980-2015) emissions determine the elemental carbon deposition trend at Holtedahlfonna glacier, Svalbard?
- 2017
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Ingår i: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 17:20, s. 12779-12795
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Tidskriftsartikel (refereegranskat)abstract
- The climate impact of black carbon (BC) is notably amplified in the Arctic by its deposition, which causes albedo decrease and subsequent earlier snow and ice spring melt. To comprehensively assess the climate impact of BC in the Arctic, information on both atmospheric BC concentrations and deposition is essential. Currently, Arctic BC deposition data are very scarce, while atmospheric BC concentrations have been shown to generally decrease since the 1990s. However, a 300-year Svalbard ice core showed a distinct increase in EC (elemental carbon, proxy for BC) deposition from 1970 to 2004 contradicting atmospheric measurements and modelling studies. Here, our objective was to decipher whether this increase has continued in the 21st century and to investigate the drivers of the observed EC deposition trends. For this, a shallow firn core was collected from the same Svalbard glacier, and a regional-to-meso-scale chemical transport model (SILAM) was run from 1980 to 2015. The ice and firn core data indicate peaking EC deposition values at the end of the 1990s and lower values thereafter. The modelled BC deposition results generally support the observed glacier EC variations. However, the ice and firn core results clearly deviate from both measured and modelled atmospheric BC concentration trends, and the modelled BC deposition trend shows variations seemingly independent from BC emission or atmospheric BC concentration trends. wet-deposited at this Svalbard glacier, indicating that meteorological processes such as precipitation and scavenging efficiency have most likely a stronger influence on the BC deposition trend than BC emission or atmospheric concentration trends. BC emission source sectors contribute differently to the modelled atmospheric BC concentrations and BC deposition, which further supports our conclusion that different processes affect atmospheric BC concentration and deposition trends. Consequently, Arctic BC deposition trends should not directly be inferred based on atmospheric BC measurements, and more observational BC deposition data are required to assess the climate impact of BC in Arctic snow.
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| 13. |
- Spolaor, Andrea, et al.
(författare)
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Climate change is rapidly deteriorating the climatic signal in Svalbard glaciers
- 2024
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Ingår i: CRYOSPHERE. - 1994-0416 .- 1994-0424. ; 18:1, s. 307-320
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Tidskriftsartikel (refereegranskat)abstract
- The Svalbard archipelago is particularly sensitive to climate change due to the relatively low altitude of its main ice fields and its geographical location in the higher North Atlantic, where the effect of Arctic amplification is more significant. The largest temperature increases have been observed during winter, but increasing summer temperatures, above the melting point, have led to increased glacier melt. Here, we evaluate the impact of this increased melt on the preservation of the oxygen isotope ( delta 18 O) signal in firn records. delta 18 O is commonly used as a proxy for past atmospheric temperature reconstructions, and, when preserved, it is a crucial parameter to date and align ice cores. By comparing four different firn cores collected in 2012, 2015, 2017 and 2019 at the top of the Holtedahlfonna ice field (1100 m a.s.l.), we show a progressive deterioration of the isotope signal, and we link its degradation to the increased occurrence and intensity of melt events. Our findings indicate that, starting from 2015, there has been an escalation in melting and percolation resulting from changes in the overall atmospheric conditions. This has led to the deterioration of the climate signal preserved within the firn or ice. Our observations correspond with the model's calculations, demonstrating an increase in water percolation since 2014, potentially reaching deeper layers of the firn. Although the delta 18 O signal still reflects the interannual temperature trend, more frequent melting events may in the future affect the interpretation of the isotopic signal, compromising the use of Svalbard ice cores. Our findings highlight the impact and the speed at which Arctic amplification is affecting Svalbard's cryosphere.
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| 14. |
- Vega, Carmen P., et al.
(författare)
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A synthetic ice core approach to estimate ion relocation in anice field site experiencing periodical melt : a case study onLomonosovfonna, Svalbard
- 2016
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Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 10, s. 961-976
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Tidskriftsartikel (refereegranskat)abstract
- Physical and chemical properties of four different ice cores (LF-97, LF-08, LF-09 and LF-11) drilled at Lomonosovfonna, Svalbard, were compared to investigate the effects of meltwater percolation on the chemical and physical stratigraphy of these records. A synthetic ice core approach was employed as reference record to estimate the ionic relocation and meltwater percolation length at this site during the period 2007-2010. Using this method, a partial ion elution sequence obtained for Lomonosovfonna was NO(3)(-)aEuro-> aEuro-SO42-, Mg2+, Cl-, K+, Na+ with nitrate being the most mobile within the snowpack. The relocation length of most of the ions was on the order of 1aEuro-m during this period. In addition, by using both a positive degree day (PDD) and a snow-energy model approaches to estimate the percentage of melt at Lomonosovfonna, we have calculated a melt percentage (MP) of the total annual accumulation within the range between 48 and 70aEuro-%, for the period between 2007 and 2010, which is above the MP range suggested by the ion relocation evidenced in the LF-syn core (i.e., MPaEuro-aEuro parts per thousand= aEuro-30aEuro-%). Using a firn-densification model to constrain the melt range, a MP of 30aEuro-% was found over the same period, which is consistent with the results of the synthetic ice core approach, and a 45aEuro-% of melt for the last 60 years. Considering the ionic relocation lengths and annual melt percentages, we estimate that the atmospheric ionic signal remains preserved in recently drilled Lomonosovfonna ice cores at an annual or bi-annual resolution when weather conditions were similar to those during the 2007-2010 period.
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| 15. |
- Vega, Carmen, et al.
(författare)
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Variability of sea salts in ice and firn cores from Fimbul Ice Shelf, Dronning Maud Land, Antarctica
- 2018
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Ingår i: The Cryosphere. - : COPERNICUS GESELLSCHAFT MBH. - 1994-0416 .- 1994-0424. ; 12:5, s. 1681-1697
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Tidskriftsartikel (refereegranskat)abstract
- Major ions were analysed in firn and ice cores located at Fimbul Ice Shelf (FIS), Dronning Maud Land - DML, Antarctica. FIS is the largest ice shelf in the Haakon VII Sea, with an extent of approximately 36 500 km(2). Three shallow firn cores (about 20m deep) were retrieved in different ice rises, Kupol Ciolkovskogo (KC), Kupol Moskovskij (KM), and Blaskimen Island (BI), while a 100m long core (S100) was drilled near the FIS edge. These sites are distributed over the entire FIS area so that they provide a variety of elevation (50-400ma. s.l.) and distance (3-42 km) to the sea. Sea-salt species (mainly Na+ and Cl-) generally dominate the precipitation chemistry in the study region. We associate a significant sixfold increase in median sea-salt concentrations, observed in the S100 core after the 1950s, to an enhanced exposure of the S100 site to primary sea-salt aerosol due to a shorter distance from the S100 site to the ice front, and to enhanced sea-salt aerosol production from blowing salty snow over sea ice, most likely related to the calving of Trolltunga occurred during the 1960s. This increase in sea-salt concentrations is synchronous with a shift in non-seasalt sulfate (nssSO2 4) toward negative values, suggesting a possible contribution of fractionated aerosol to the sea-salt load in the S100 core most likely originating from salty snow found on sea ice. In contrast, there is no evidence of a significant contribution of fractionated sea salt to the ice-rises sites, where the signal would be most likely masked by the large inputs of biogenic sulfate estimated for these sites. In summary, these results suggest that the S100 core contains a sea-salt record dominated by the proximity of the site to the ocean, and processes of sea ice formation in the neighbouring waters. In contrast, the ice-rises firn cores register a larger-scale signal of atmospheric flow conditions and a less efficient transport of sea-salt aerosols to these sites. These findings are a contribution to the understanding of the mechanisms behind sea-salt aerosol production, transport and deposition at coastal Antarctic sites, and the improvement of the current Antarctic sea ice reconstructions based on sea-salt chemical proxies obtained from ice cores.
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