| 1. |
- Dahl-Jensen, D., et al.
(författare)
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Eemian interglacial reconstructed from a Greenland folded ice core
- 2013
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 493:7433, s. 489-494
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Tidskriftsartikel (refereegranskat)abstract
- Efforts to extract a Greenland ice core with a complete record of the Eemian interglacial (130,000 to 115,000 years ago) have until now been unsuccessful. The response of the Greenland ice sheet to the warmer-than-present climate of the Eemian has thus remained unclear. Here we present the new North Greenland Eemian Ice Drilling ('NEEM') ice core and show only a modest ice-sheet response to the strong warming in the early Eemian. We reconstructed the Eemian record from folded ice using globally homogeneous parameters known from dated Greenland and Antarctic ice-core records. On the basis of water stable isotopes, NEEM surface temperatures after the onset of the Eemian (126,000 years ago) peaked at 8 +/- 4 degrees Celsius above the mean of the past millennium, followed by a gradual cooling that was probably driven by the decreasing summer insolation. Between 128,000 and 122,000 years ago, the thickness of the northwest Greenland ice sheet decreased by 400 +/- 250 metres, reaching surface elevations 122,000 years ago of 130 +/- 300 metres lower than the present. Extensive surface melt occurred at the NEEM site during the Eemian, a phenomenon witnessed when melt layers formed again at NEEM during the exceptional heat of July 2012. With additional warming, surface melt might become more common in the future.
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| 2. |
- Pattyn, F., et al.
(författare)
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Melting and refreezing beneath Roi Baudouin Ice Shelf (East Antarctica) inferred from radar, GPS, and ice core data
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117, s. F04008-
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Tidskriftsartikel (refereegranskat)abstract
- Ice-penetrating radar profiles across the grounding line of a small ice-rise promontory located within the Roi Baudouin Ice Shelf in the Dronning Maud Land sector of East Antarctica show downward dipping englacial radar-detected reflectors. Model results indicate that this reflector pattern is best fit by including basal melting of at least 15 cm a(-1). This rate of melting is low compared with rates observed on larger ice shelves in both West and East Antarctica. Ice cores extracted from a rift system close to the ice-rise promontory show several meters of marine ice accreted beneath the shelf. These observations of low rates of basal melting, and limited distribution of accreted marine ice suggest that either Antarctic surface water may reach the ice shelf base or that circulation beneath the shelf is likely dominated by the production of high salinity shelf water rather than the incursion of circumpolar deep water, implying a weak sub-shelf circulation system here. Many of the ice shelves located along the coast of Dronning Maud Land are, like Roi Baudouin Ice Shelf, characterized by frequent ice rises and promontories. Therefore, it is highly likely that these are also of shallow bathymetry and are subject to similarly weak side-shelf basal melting and refreezing.
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| 3. |
- Tison, J.-L., et al.
(författare)
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Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core
- 2015
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Ingår i: The Cryosphere. - : Copernicus GmbH. - 1994-0416 .- 1994-0424. ; 9:4, s. 1633-1648
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Tidskriftsartikel (refereegranskat)abstract
- An important share of paleoclimatic information is buried within the lowermost layers of deep ice cores. Because improving our records further back in time is one of the main challenges in the near future, it is essential to judge how deep these records remain unaltered, since the proximity of the bedrock is likely to interfere both with the recorded temporal sequence and the ice properties. In this paper, we present a multiparametric study (delta D-delta O-18(ice), delta O-18(atm), total air content, CO2, CH4, N2O, dust, high-resolution chemistry, ice texture) of the bottom 60 m of the EPICA (European Project for Ice Coring in Antarctica) Dome C ice core from central Antarctica. These bottom layers were subdivided into two distinct facies: the lower 12 m showing visible solid inclusions (basal dispersed ice facies) and the upper 48 m, which we will refer to as the basal clean ice facies. Some of the data are consistent with a pristine paleoclimatic signal, others show clear anomalies It is demonstrated that neither large-scale bottom refreezing of subglacial water, nor mixing (be it internal or with a local basal end term from a previous/initial ice sheet configuration) can explain the observed bottom-ice properties. We focus on the high-resolution chemical profiles and on the available remote sensing data on the subglacial topography of the site to propose a mechanism by which relative stretching of the bottom-ice sheet layers is made possible, due to the progressively confining effect of subglacial valley sides. This stress field change, combined with bottom-ice temperature close to the pressure melting point, induces accelerated migration recrystallization, which results in spatial chemical sorting of the impurities, depending on their state (dissolved vs. solid) and if they are involved or not in salt formation. This chemical sorting effect is responsible for the progressive build-up of the visible solid aggregates that therefore mainly originate from within, and not from incorporation processes of debris from the ice sheet's substrate. We further discuss how the proposed mechanism is compatible with the other ice properties described. We conclude that the paleoclimatic signal is only marginally affected in terms of global ice properties at the bottom of EPICA Dome C, but that the timescale was considerably distorted by mechanical stretching of MIS20 due to the increasing influence of the subglacial topography, a process that might have started well above the bottom ice. A clear paleoclimatic signal can therefore not be inferred from the deeper part of the EPICA Dome C ice core. Our work suggests that the existence of a flat monotonic ice bedrock interface, extending for several times the ice thickness, would be a crucial factor in choosing a future oldest ice drilling location in Antarctica.
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| 4. |
- Christakopoulos, Paul, et al.
(författare)
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Functional characterization of a cellulose binding xylanase from Fusarium oxysporum
- 1996
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Ingår i: Biotechnology letters. - 0141-5492 .- 1573-6776. ; 18:3, s. 349-354
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Tidskriftsartikel (refereegranskat)abstract
- An extracellular endoxylanase from Fusarium oxysporum binds onto crystalline cellulose. A small peptide (~ 2kDa) could be isolated after partial proteolysis of the native protein. It consists of 18 amino acids, is located in the C-terminal region of the protein and corresponds functionally to a cellulose binding domain (CBD), the first one to be reported in a fungal xylanase. The amino acid sequence of this peptide shows no homology with any known CBD
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| 5. |
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| 6. |
- Ruiz-Pavon, L, et al.
(författare)
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Modeling and Mutational analysis of Anion transporter 1 protein of Arabidopsis thaliana
- 2010
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Ingår i: The FEBS Journal. - : Wiley-Blackwell. - 1742-464X .- 1742-4658. ; 277:Suppl. 1, s. 231-231
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The thylakoid anion transporter 1 (ANTR1) from Arabidopsisthaliana, has been characterized as a Na-dependent Pi transporter when expressed in E. coli (1), but no data is yet available for the protein structure and amino acids involved in transport of Pi. In this study a three-dimensional structural model of ANTR1 was constructed in silico using the crystal structure of glycerol-3- phosphate/phosphate antiporter from E. coli as a template. Based on Multiple Sequence Alignments (MSAs) with other plant ANT- Rs and mammalian SLC17 homologues, five highly conserved amino acids involved in Pi transport have been identified, namely Arg-120, Ser-124 and Arg-201 inside the putative translocation pathway, Arg-228 and Asp-382 exposed at the cytoplasmic sur- face of the protein. The activity of the protein as a Na-dependent Pi transporter in the wild type and mutants was analyzed by het- erologous expression and uptake of radioactive Pi into E. coli cells. Substitution of the three Arg (120, 201 and 228) for Glu residues and of Asp-382 for an Asn residue resulted in an inac- tive ANTR1 transporter. All other mutants had sufficient activity to allow measurement of kinetic parameters, attesting that the mutated proteins were functional. Based on our results, we pro- pose that Arg-201 is a critical residue for substrate binding and translocation, whereas Ser-124 may function as periplasmic gate- way for Na+ ions. Residue Arg-120 plays an important role in Pi binding and associated conformational changes, and finally that Arg-228 and Asp-382 only weakly participate in interactions allowing conformational changes to occur at the cytoplasmic sur-face of the transporter.
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| 7. |
- Samyn, D., et al.
(författare)
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Nitrate and Sulfate Anthropogenic Trends in the 20th Century from Five Svalbard Ice Cores
- 2012
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Ingår i: Arctic, Antarctic and Alpine research. - : Informa UK Limited. - 1523-0430 .- 1938-4246. ; 44:4, s. 490-499
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Tidskriftsartikel (refereegranskat)abstract
- Sulfate and nitrate records from 5 ice cores spread across Svalbard were compared and revealed strong temporal similarities with previously published global estimates of SO2 and NOx anthropogenic emissions during the 20th century. A significant departure from the early century sulfate and nitrate levels was evident at all drilling sites starting from the mid-1940s. A steady increase was observed in both sulfate and nitrate profiles at most sites until the late 1960s, when the annual concentrations started to increase at a higher rate. This peak activity lasted for about a decade, and was observed to decrease steadily from the early 1980s on, when sulfate levels declined significantly and when nitrate levels finally reached sulfate levels for the first time in 20th century. The timing of these trends in Svalbard with global SO2 and NOx concentration profiles was best appraised when considering composite concentration profiles of all Svalbard ice cores for sulfate and nitrate, respectively. Composite profiles were also found to provide a convenient mean for distinguishing between the most important world source regions. Based on correlation analysis, the major pollutant sources appeared to be Western Europe and North America for both sulfate and nitrate, followed by Central Europe and former U.S.S.R. in generally similar proportions.
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| 8. |
- Samyn, Denis, et al.
(författare)
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Rotating micro-structures in Antarctic cold basal ice : implications for glacier flow and its interpretation
- 2010
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Ingår i: International journal of earth sciences. - : Springer Science and Business Media LLC. - 1437-3254 .- 1437-3262. ; 99:8, s. 1849-1857
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Tidskriftsartikel (refereegranskat)abstract
- Structural analyses were conducted in the basal zone of an Antarctic glacier The studied basal ice sequence was retrieved from a 20-m-long subglacial tunnel dug at the margin of the glacier and is at the temperature of -17 degrees C For the first time, rotating clast systems embedded within debris-rich ice were thin-sectioned using specially designed cutting techniques The observed structures reflect the occurrence of pervasive shearing at the base of the glacier, and can be used as shear sense indicators In addition, some of these structures provide evidence for the presence of thin liquid films at the time of formation despite the marked freezing temperature of the ice It is showed here that cautious analysis of deformation structures present in debris-bearing ice may bring insights not only into the flow dynamics of the embedding matrix, but also Into the behaviour of the interstitial fluid network at the base of cold glaciers and ice sheets.
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| 9. |
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| 10. |
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