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  • 1. Berggren, A. -M
    et al.
    Aldahan, A.
    Possnert, G.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Steen-Larsen, H. C.
    Storm, A. Sturevik
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Murad, A.
    Variability of Be-10 and delta O-18 in snow pits from Greenland and a surface traverse from Antarctica2013In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 294, p. 568-572Article in journal (Refereed)
    Abstract [en]

    To examine temporal variability of Be-10 in glacial ice, we sampled snow to a depth of 160 cm at the NEEM (North Greenland Eemian Ice Drilling) drilling site in Greenland. The samples span three years between the summers of 2006 and 2009. At the same time, spatial variability of Be-10 in glacial ice was explored through collection of the upper similar to 5 cm of surface snow in Antarctica during part of the Swedish-Japanese traverse from Svea to Syowa station during the austral summer in 2007-2008. The results of the Greenlandic 1 Be snow suggested variable concentrations that apparently do not clearly reflect the seasonal change as indicated by the delta O-18 data. The Be-10 concentration variability most likely reflects also effects of aerosol loading and deposition pathways, possibly in combination with post-depositional processes. The Antarctic traverse data expose a negative correlation between Be-10 and delta O-18, while there are weaker but still significant correlations to altitude and distance to the coast (approximated by the distance to the 70th latitude). These relationships indicate that geographical factors, mainly the proximity to the coast, may strongly affect 1 Be concentrations in snow in Queen Maud Land, Antarctica.

  • 2. Dahl-Jensen, D.
    et al.
    Albert, M. R.
    Aldahan, A.
    Azuma, N.
    Balslev-Clausen, D.
    Baumgartner, M.
    Berggren, A. -M
    Bigler, M.
    Binder, T.
    Blunier, T.
    Bourgeois, J. C.
    Brook, E. J.
    Buchardt, S. L.
    Buizert, C.
    Capron, E.
    Chappellaz, J.
    Chung, J.
    Clausen, H. B.
    Cvijanovic, I.
    Davies, S. M.
    Ditlevsen, P.
    Eicher, O.
    Fischer, H.
    Fisher, D. A.
    Fleet, L. G.
    Gfeller, G.
    Gkinis, V.
    Gogineni, S.
    Goto-Azuma, K.
    Grinsted, A.
    Gudlaugsdottir, H.
    Guillevic, M.
    Hansen, S. B.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hirabayashi, M.
    Hong, S.
    Hur, S. D.
    Huybrechts, P.
    Hvidberg, C. S.
    Iizuka, Yoshinori
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Hokkaido University, Japan.
    Jenk, T.
    Johnsen, S. J.
    Jones, T. R.
    Jouzel, J.
    Karlsson, N. B.
    Kawamura, K.
    Keegan, K.
    Kettner, E.
    Kipfstuhl, S.
    Kjaer, H. A.
    Koutnik, M.
    Kuramoto, T.
    Koehler, P.
    Laepple, T.
    Landais, A.
    Langen, P. L.
    Larsen, L. B.
    Leuenberger, D.
    Leuenberger, M.
    Leuschen, C.
    Li, J.
    Lipenkov, V.
    Martinerie, P.
    Maselli, O. J.
    Masson-Delmotte, V.
    McConnell, J. R.
    Miller, H.
    Mini, O.
    Miyamoto, A.
    Montagnat-Rentier, M.
    Mulvaney, R.
    Muscheler, R.
    Orsi, A. J.
    Paden, J.
    Panton, C.
    Pattyn, F.
    Petit, J. -R
    Pol, K.
    Popp, T.
    Possnert, G.
    Prie, F.
    Prokopiou, M.
    Quiquet, A.
    Rasmussen, S. O.
    Raynaud, D.
    Ren, J.
    Reutenauer, C.
    Ritz, C.
    Rockmann, T.
    Rosen, J. L.
    Rubino, M.
    Rybak, O.
    Samyn, D.
    Sapart, C. J.
    Schilt, A.
    Schmidt, A. M. Z.
    Schwander, J.
    Schuepbach, S.
    Seierstad, I.
    Severinghaus, J. P.
    Sheldon, S.
    Simonsen, S. B.
    Sjolte, J.
    Solgaard, A. M.
    Sowers, T.
    Sperlich, P.
    Steen-Larsen, H. C.
    Steffen, K.
    Steffensen, J. P.
    Steinhage, D.
    Stocker, T. F.
    Stowasser, C.
    Sturevik, A. S.
    Sturges, W. T.
    Sveinbjornsdottir, A.
    Svensson, A.
    Tison, J. -L
    Uetake, J.
    Vallelonga, P.
    van de Wal, R. S. W.
    van der Wel, G.
    Vaughn, B. H.
    Vinther, B.
    Waddington, E.
    Wegner, A.
    Weikusat, I.
    White, J. W. C.
    Wilhelms, F.
    Winstrup, M.
    Witrant, E.
    Wolff, E. W.
    Xiao, C.
    Zheng, J.
    Eemian interglacial reconstructed from a Greenland folded ice core2013In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 493, no 7433, p. 489-494Article in journal (Refereed)
    Abstract [en]

    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.

  • 3. Delmonte, Barbara
    et al.
    Andersson, Per
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Schöberg, Hans
    Petit, Jean Robert
    Basile-Doelsch, Isabelle
    Maggi, Valter
    Aeolian dust in East Antarctica (EPICA-Dome C and Vostok): provenance during glacial ages over the last 800 kyr.2008In: GEOPHYSICAL RESEARCH LETTERS, ISSN 0094-8276, Vol. 35, no 7Article in journal (Refereed)
    Abstract [en]

    Aeolian mineral dust archived in Antarctic ice cores represents a key proxy for Quaternary climate evolution. The longest and most detailed dust and climate sequences from polar ice are provided today by the Vostok and by the EPICA-Dome C (EDC) ice cores. Here we investigate the geographic provenance of dust windborne to East Antarctica during Early and Middle Pleistocene glacial ages using strontium and neodymium isotopes as tracers. The isotopic signature of Antarctic dust points towards a dominant South American origin during Marine Isotopic Stage (MIS) 8, 10, 12, and back to MIS 16 and 20 as deduced from EDC core. Data provide evidence for a persistent overall westerly circulation pattern allowing efficient transfer of dust from South America to the interior of Antarctica over the last 800 kyr. Some small but significant dissimilarity between old and recent glacial ages suggests a slightly reduced Patagonian contribution during ancient glaciations.

  • 4. Delmonte, Barbara
    et al.
    Baroni, Carlo
    Andersson, Per S.
    Schoberg, Hans
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Aciego, Sarah
    Petit, Jean-Robert
    Albani, Samuel
    Mazzola, Claudia
    Maggi, Valter
    Frezzotti, Massimo
    Aeolian dust in the Talos Dome ice core (East Antarctica, Pacific/Ross Sea sector): Victoria Land versus remote sources over the last two climate cycles2010In: Journal of Quaternary Science, ISSN 0267-8179, E-ISSN 1099-1417, Vol. 25, no 8, p. 1327-1337Article in journal (Refereed)
    Abstract [en]

    A new ice core (TALDICE) drilled at Tabs Dome (East Antarctica, Ross Sea sector) preserves a ca. 250 ka long record of palaeoclimate and atmospheric history. We investigate dust variability and provenance at the site during glacial periods and the Holocene through the Sr-Nd isotopic composition of ice core dust and potential source areas (PSA). We provide new isotopic data on dust sources from Victoria Land such as regoliths, glacial drifts, aeolian sands and beach deposits. Some of these sources are located at high altitude and are known to have been ice free throughout the Pleistocene. The major features of the TALDICE dust record are very similar to those from central East Antarctica. During glacial times, South America was the dominant dust supplier for Tabs Dome as well as for the entire East Antarctic plateau. Conversely, during the Holocene the principal input of mineral dust at Tabs Dome probably derives from proximal sources which are the ice-free areas of northern Victoria Land, located at similar altitude with respect to the drilling site. Atmospheric mobilisation of dust from these neighbouring areas and transport inland to Tabs Dome can be ultimately associated with advection of maritime air masses from the Pacific/Ross Sea region. Copyright (C) 2010 John Wiley & Sons, Ltd.

  • 5. Iizuka, Yoshinori
    et al.
    Karlin, Torbjorn
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Sulphate and chloride aerosols during Holocene and last glacial periods preserved in the Talos Dome Ice Core, a peripheral region of Antarctica2013In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 65, p. 20197-Article in journal (Refereed)
    Abstract [en]

    Antarctic ice cores preserve the record of past aerosols, an important proxy of past atmospheric chemistry. Here we present the aerosol compositions of sulphate and chloride particles in the Talos Dome (TD) ice core from the Holocene and Last Glacial Period. We find that the main salt types of both periods are NaCl, Na2SO4 and CaSO4, indicating that TD ice contains relatively abundant sea salt (NaCl) from marine primary particles. By evaluating the molar ratio of NaCl to Na2SO4, we show that about half of the sea salt does not undergo sulphatisation during late Holocene. Compared to in inland Antarctica, the lower sulphatisation rate at TD is probably due to relatively little contact between sea salt and sulphuric acid. This low contact rate can be related to a reduced time of reaction for marine-sourced aerosol before reaching TD and/or to a reduced post-depositional effect from the higher accumulation rate at TD. Many sulphate and chloride salts are adhered to silicate minerals. The ratio of sulphate-adhered mineral to particle mass and the corresponding ratio of chloride-adhered mineral both increase with increasing dust concentration. Also, the TD ice appears to contain Ca(NO3)(2) or CaCO3 particles, thus differing from aerosol compositions in inland Antarctica, and indicating the proximity of peripheral regions to marine aerosols.

  • 6. Iizuka, Yoshinori
    et al.
    Tsuchimoto, Akira
    Hoshina, Yu
    Sakurai, Toshimitsu
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Karlin, Torbjörn
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Fujita, Koji
    Nakazawa, Fumio
    Motoyama, Hideaki
    Fujita, Shuji
    The rates of sea salt sulfatization in the atmosphere and surface snow of inland Antarctica2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, p. D04308-Article in journal (Refereed)
    Abstract [en]

    Most of the aerosol particles present in the surface snow and ice of inland Antarctica come from primary sea salt (sodium chloride) and marine biological activity (methansulfonic and sulfuric acids). Melted water from surface snow, firn, and Holocene ice contains mainly sodium, chloride, and sulfate ions. Although it is well known that sea salt aerosols react rapidly with sulfuric acid, a process known as sulfatization, it is not known when this process takes place. In this research we undertake to measure the proportion of sea salt aerosols that undergo sulfatization in the atmosphere and surface snow, as opposed to deeper ice, in order to understand the suitability of sea salt aerosols as a proxy for past climates in deep ice cores. We directly measure the sulfatization rates in recently fallen snow (0-4 m in depth) collected at the Dome Fuji station, using X-ray dispersion spectroscopy to determine the constituent elements of soluble particles and computing the molar ratios of sodium chloride and sodium sulfate. We estimate that about 90% of the initial sea salt aerosols sulfatize as they are taken up by precipitation over Dome Fuji or in the snowpack within one year after being deposited on the ice sheet.

  • 7.
    Ingvander, Susanne
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Jansson, Peter
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Brown, Ian A.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Fujita, Shuji
    Sugyama, Shin
    Surdyk, Sylviane
    Enomoto, Hiroyuki
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Holmlund, Per
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Snow particle sizes and their distributions in Dronning Maud Land, Antarctica, at sample, local and regional scales2016In: Antarctic Science, ISSN 0954-1020, E-ISSN 1365-2079, Vol. 28, no 3, p. 219-231Article in journal (Refereed)
    Abstract [en]

    In this study, snow particle size variability was investigated along a transect in Dronning Maud Land from the coast to the polar plateau. The aim of the study was to better understand the spatial and temporal variations in surface snow properties. Samples were collected twice daily during a traverse in 2007-08 to capture regional variability. Local variability was assessed by sampling in 10 x 10m grids (5m spacing) at selected locations. The particle size and shape distributions for each site were analysed through digital image analysis. Snow particle size variability is complex at different scales, and shows an internal variability of 0.18-3.31 mm depending on the sample type (surface, grid or pit). Relationships were verified between particle size and both elevation and distance to the coast (moisture source). Regional seasonal changes were also identified, particularly on the lower elevations of the polar plateau. This dataset may be used to quantitatively analyse the optical properties of surface snow for remote sensing. The details of the spatial and temporal variations observed in our data provide a basis for further studies of the complex and coupled processes affecting snow particle size and the interpretation of remote sensing of snow covered areas.

  • 8.
    Jonsell, Ulf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Hansson, Margareta E.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Mörth, Carl-Magnus
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Correlations between concentrations of acids andoxygen isotope ratios in polar surface snow2007In: Tellus. Series B, Chemical and physical meteorology, ISSN 0280-6509, E-ISSN 1600-0889, Vol. 59b, p. 326-335Article in journal (Refereed)
    Abstract [en]

      

     

     

     

     

    Investigation of centimeter-scale snow surface chemistry has been carried out at two polar sites with different site

    characteristics–in Dronning Maud Land, Antarctica and on the Greenland ice sheet, respectively. Large variations

    in both impurity content and stable oxygen isotope ratios (

     

    δ18O) were found on the submeter scale. δ18

    O and the

    concentration of nitrate correlated at both sites (r

     

    = 0.81 and 0.82, respectively). At the Antarctic site, δ18

    O is also

    correlated to concentrations of methanesulphonate (r

     

    = 0.84) and sulphate (r =

    0.83) while no such correlation exists

    at the Greenland site. Instead, a strong anticorrelation (r

     

    =

    –0.85) between sulphate and methanesulphonate is found

    among the samples from the Greenland site. The ions correlating with

     

    δ18

    O at the two sites were probably deposited as

    acids. Our tentative explanation is that local redeposition of water vapour enriching the snow surface with the lighter

    isotopes is associated with simultaneous enhanced scavenging of the acids. The responsible process thereby significantly

    alters the chemical signals of the snow surface.

  • 9.
    Jonsell, Ulf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Mörth, Carl-Magnus
    Department of Geology and Geochemistry.
    Correlation between concentrations of acids and oxygen isotope ratios in polar surface snow caused by local redeposition2007In: Tellus: B, Vol. 59, no 2, p. 326-335Article in journal (Refereed)
    Abstract [en]

    Investigation of centimeter-scale snow surface chemistry has been carried out at two polar sites with different site characteristics–in Dronning Maud Land, Antarctica and on the Greenland ice sheet, respectively. Large variations in both impurity content and stable oxygen isotope ratios (δ18O) were found on the submeter scale. δ18O and the concentration of nitrate correlated at both sites (r = 0.81 and 0.82, respectively). At the Antarctic site, δ18O is also correlated to concentrations of methanesulphonate (r = 0.84) and sulphate (r = 0.83) while no such correlation exists at the Greenland site. Instead, a strong anticorrelation (r = –0.85) between sulphate and methanesulphonate is found among the samples from the Greenland site. The ions correlating with δ18O at the two sites were probably deposited as acids. Our tentative explanation is that local redeposition of water vapour enriching the snow surface with the lighter isotopes is associated with simultaneous enhanced scavenging of the acids. The responsible process thereby significantly alters the chemical signals of the snow surface.

  • 10.
    Jonsell, Ulf
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Siggard-Andresen, Marie-Louise
    Steffensen, Jörgen-Peder
    Comparison of northern and central Greenland ice core records of methanesulfonate covering the last glacial period2007In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, no D14313Article in journal (Refereed)
    Abstract [en]

    Methanesulfonate (MS) is measured in ice cores with the objective to obtain a proxy record of marine phytoplankton production of dimethylsulfide (DMS). We present a continuous MS record covering the last glacial period from the North Greenland Ice Core Project (NGRIP) ice core and compare this record with the corresponding records previously presented from Greenland and, in particular, with the GISP2 ice core located 320 km south of NGRIP. Despite that the records have similar mean concentrations, their responses to climatic changes during the last glacial period are slightly different. NGRIP MS concentrations were higher during the cold marine isotopic stages (MIS) 2 and 4 and lower during the warm MIS 5. This long-term trend in MS, which is similar to the inverse of the corresponding trend in δ 18O, is not detected in the GISP2 MS record. A systematic response in MS concentrations to changes between Greenland stadials and interstadials is only detected in the GISP2 record. The different responses of the MS signals to climate change during the last glacial period are possibly related to the partitioning of air masses reaching the two sites. In contrast to observations from Antarctic records, dust concentrations do not affect the MS concentrations in the ice, whereas the deposition of sulfate probably is enhanced by high dust concentrations in the atmosphere. The MS signal has a higher potential of being a proxy record of DMS production changes in Greenlandic compared to Antarctic ice cores.

  • 11.
    Oyabu, Ikumi
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography. Hokkaido University, Japan.
    Iizuka, Yoshinori
    Fischer, Hubertus
    Schuepbach, Simon
    Gfeller, Gideon
    Svensson, Anders
    Fukui, Manabu
    Steffensen, Jörgen Peder
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Chemical compositions of solid particles present in the Greenland NEEM ice core over the last 110,000 years2015In: Journal of Geophysical Research - Atmospheres, ISSN 2169-897X, E-ISSN 2169-8996, Vol. 120, no 18, p. 9789-9813Article in journal (Refereed)
    Abstract [en]

    This study reports the chemical composition of particles present along Greenland's North Greenland Eemian Ice Drilling (NEEM) ice core, back to 110,000years before present. Insoluble and soluble particles larger than 0.45 mu m were extracted from the ice core by ice sublimation, and their chemical composition was analyzed using scanning electron microscope and energy dispersive X-ray spectroscopy and micro-Raman spectroscopy. We show that the dominant insoluble components are silicates, whereas NaCl, Na2SO4, CaSO4, and CaCO3 represent major soluble salts. For the first time, particles of CaMg(CO3)(2) and Ca(NO3)(2)center dot 4H(2)O are identified in a Greenland ice core. The chemical speciation of salts varies with past climatic conditions. Whereas the fraction of Na salts (NaCl+Na2SO4) exceeds that of Ca salts (CaSO4+CaCO3) during the Holocene (0.6-11.7kyr B.P.), the two fractions are similar during the BOlling-AllerOd period (12.9-14.6kyr B.P.). During cold climate such as over the Younger Dryas (12.0-12.6kyr B.P.) and the Last Glacial Maximum (15.0-26.9kyr B.P.), the fraction of Ca salts exceeds that of Na salts, showing that the most abundant ion generally controls the salt budget in each period. High-resolution analyses reveal changing particle compositions: those in Holocene ice show seasonal changes, and those in LGM ice show a difference between cloudy bands and clear layers, which again can be largely explained by the availability of ionic components in the atmospheric aerosol body of air masses reaching Greenland.

  • 12. Persoiu, Aurel
    et al.
    Onac, Bogdan P.
    Wynn, Jonathan G.
    Blaauw, Maarten
    Ionita, Monica
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Holocene winter climate variability in Central and Eastern Europe2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 1196Article in journal (Refereed)
    Abstract [en]

    Among abundant reconstructions of Holocene climate in Europe, only a handful has addressed winter conditions, and most of these are restricted in length and/or resolution. Here we present a record of late autumn through early winter air temperature and moisture source changes in East-Central Europe for the Holocene, based on stable isotopic analysis of an ice core recovered from a cave in the Romanian Carpathian Mountains. During the past 10,000 years, reconstructed temperature changes followed insolation, with a minimum in the early Holocene, followed by gradual and continuous increase towards the mid-to-late-Holocene peak (between 4-2 kcal BP), and finally by a decrease after 0.8 kcal BP towards a minimum during the Little Ice Age (AD 1300-1850). Reconstructed early Holocene atmospheric circulation patterns were similar to those characteristics of the negative phase of the North Atlantic Oscillation (NAO), while in the late Holocene they resembled those prevailing in the positive NAO phase. The transition between the two regimes occurred abruptly at around 4.7 kcal BP. Remarkably, the widespread cooling at 8.2 kcal BP is not seen very well as a temperature change, but as a shift in moisture source, suggesting weaker westerlies and increased Mediterranean cyclones penetrating northward at this time.

  • 13. Roethlisberger, R.
    et al.
    Mudelsee, M.
    Bigler, M.
    de Angelis, M.
    Fischer, H.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology (INK).
    Lambert, F.
    Masson-Delmotte, V.
    Sime, L.
    Udisti, R.
    Wolff, E. W.
    The Southern Hemisphere at glacial terminations: insights from the Dome C ice core2008In: Climate of the past, ISSN 1814-9324, Vol. 4, no 4, p. 345-356Article in journal (Refereed)
    Abstract [en]

    The many different proxy records from the European Project for Ice Coring in Antarctica (EPICA) Dome C ice core allow for the first time a comparison of nine glacial terminations in great detail. Despite the fact that all terminations cover the transition from a glacial maximum into an interglacial, there are large differences between single terminations. For some terminations, Antarctic temperature increased only moderately, while for others, the amplitude of change at the termination was much larger. For the different terminations, the rate of change in temperature is more similar than the magnitude or duration of change. These temperature changes were accompanied by vast changes in dust and sea salt deposition all over Antarctica. Here we investigate the phasing between a South American dust proxy (non-sea-salt calcium flux, nssCa(2+)), a sea ice proxy (sea salt sodium flux, ssNa(+)) and a proxy for Antarctic temperature (deuterium, delta D). In particular, we look into whether a similar sequence of events applies to all terminations, despite their different characteristics. All proxies are derived from the EPICA Dome C ice core, resulting in a relative dating uncertainty between the proxies of less than 20 years. At the start of the terminations, the temperature (delta D) increase and dust (nssCa(2+) flux) decrease start synchronously. The sea ice proxy (ssNa(+) flux), however, only changes once the temperature has reached a particular threshold, approximately 5 degrees C below present day temperatures (corresponding to a delta D value of -420 parts per thousand). This reflects to a large extent the limited sensitivity of the sea ice proxy during very cold periods with large sea ice extent. At terminations where this threshold is not reached (TVI, TVIII), ssNa(+) flux shows no changes. Above this threshold, the sea ice proxy is closely coupled to the Antarctic temperature, and interglacial levels are reached at the same time for both ssNa(+) and delta D. On the other hand, once another threshold at approximately 2 degrees C below present day temperature is passed (corresponding to a delta D value of -402 parts per thousand), nssCa(2+) flux has reached interglacial levels and does not change any more, despite further warming. This threshold behaviour most likely results from a combination of changes to the threshold friction velocity for dust entrainment and to the distribution of surface wind speeds in the dust source region.

  • 14. Schupbach, S.
    et al.
    Fischer, H.
    Bigler, M.
    Erhardt, T.
    Gfeller, G.
    Leuenberger, D.
    Mini, O.
    Mulvaney, R.
    Abram, N. J.
    Fleet, L.
    Frey, M. M.
    Thomas, E.
    Svensson, A.
    Dahl-Jensen, D.
    Kettner, E.
    Kjaer, H.
    Seierstad, I.
    Steffensen, J. P.
    Rasmussen, S. O.
    Vallelonga, P.
    Winstrup, M.
    Wegner, A.
    Twarloh, B.
    Wolff, K.
    Schmidt, K.
    Goto-Azuma, K.
    Kuramoto, T.
    Hirabayashi, M.
    Uetake, J.
    Zheng, J.
    Bourgeois, J.
    Fisher, D.
    Zhiheng, D.
    Xiao, C.
    Legrand, M.
    Spolaor, A.
    Gabrieli, J.
    Barbante, C.
    Kang, J. -H.
    Hur, S. D.
    Hong, S. B.
    Hwang, H. J.
    Hong, S.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Iizuka, Yoshinori
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Oyabu, Ikumi
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Muscheler, R.
    Adolphi, F.
    Maselli, O.
    McConnell, J.
    Wolff, E. W.
    Greenland records of aerosol source and atmospheric lifetime changes from the Eemian to the Holocene2018In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 9, article id 1476Article in journal (Refereed)
    Abstract [en]

    The Northern Hemisphere experienced dramatic changes during the last glacial, featuring vast ice sheets and abrupt climate events, while high northern latitudes during the last interglacial (Eemian) were warmer than today. Here we use high-resolution aerosol records from the Greenland NEEM ice core to reconstruct the environmental alterations in aerosol source regions accompanying these changes. Separating source and transport effects, we find strongly reduced terrestrial biogenic emissions during glacial times reflecting net loss of vegetated area in North America. Rapid climate changes during the glacial have little effect on terrestrial biogenic aerosol emissions. A strong increase in terrestrial dust emissions during the coldest intervals indicates higher aridity and dust storm activity in East Asian deserts. Glacial sea salt aerosol emissions in the North Atlantic region increase only moderately (50%), likely due to sea ice expansion. Lower aerosol concentrations in Eemian ice compared to the Holocene are mainly due to shortened atmospheric residence time, while emissions changed little.

  • 15.
    Ström, Johan
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Zábori, Julia
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Krejci, Radovan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Ekman, Annica
    Stockholm University, Faculty of Science, Department of Meteorology .
    Tunved, Peter
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Arctic Ocean water:  A source of light absorbing particles to the atmosphereArticle in journal (Refereed)
  • 16. Svensson, J.
    et al.
    Ström, Johan
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Lihavainen, H.
    Kerminen, V-M
    Observed metre scale horizontal variability of elemental carbon in surface snow2013In: Environmental Research Letters, ISSN 1748-9326, E-ISSN 1748-9326, Vol. 8, no 3, p. 034012-Article in journal (Refereed)
    Abstract [en]

    Surface snow investigated for its elemental carbon (EC) concentration, based on a thermal-optical method, at two different sites during winter and spring of 2010 demonstrates metre scale horizontal variability in concentration. Based on the two sites sampled, a clean and a polluted site, the clean site (Arctic Finland) presents the greatest variability. In side-by-side ratios between neighbouring samples, 5 m apart, a ratio of around two was observed for the clean site. The median for the polluted site had a ratio of 1.2 between neighbouring samples. The results suggest that regions exposed to snowdrift may be more sensitive to horizontal variability in EC concentration. Furthermore, these results highlight the importance of carefully choosing sampling sites and timing, as each parameter will have some effect on EC variability. They also emphasize the importance of gathering multiple samples from a site to obtain a representative value for the area.

  • 17. Tison, J.-L.
    et al.
    de Angelis, M.
    Littot, G.
    Wolff, E.
    Fischer, H.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Bigler, M.
    Udisti, R.
    Wegner, A.
    Jouzel, J.
    Stenni, B.
    Johnsen, S.
    Masson-Delmotte, V.
    Landais, A.
    Lipenkov, V.
    Loulergue, L.
    Barnola, J. -M.
    Petit, J. -R.
    Delmonte, B.
    Dreyfus, G.
    Dahl-Jensen, D.
    Durand, G.
    Bereiter, B.
    Schilt, A.
    Spahni, R.
    Pol, K.
    Lorrain, R.
    Souchez, R.
    Samyn, D.
    Retrieving the paleoclimatic signal from the deeper part of the EPICA Dome C ice core2015In: The Cryosphere, ISSN 1994-0416, E-ISSN 1994-0424, Vol. 9, no 4, p. 1633-1648Article in journal (Refereed)
    Abstract [en]

    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.

  • 18. Wolff, E. W.
    et al.
    Barbante, C.
    Becagli, S.
    Bigler, M.
    Boutron, C. F.
    Castellano, E.
    de Angelis, M.
    Federer, U.
    Fischer, H.
    Fundel, F.
    Hansson, Margareta
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Hutterli, M.
    Jonsell, Ulf
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Karlin, Torbjörn
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Kaufmann, P.
    Lambert, F.
    Littot, G. C.
    Mulvaney, R.
    Roethlisberger, R.
    Ruth, U.
    Severi, M.
    Siggaard-Andersen, M. L.
    Sime, L. C.
    Steffensen, J. P.
    Stocker, T. F.
    Traversi, R.
    Twarloh, B.
    Udisti, R.
    Wagenbach, D.
    Wegner, A.
    Changes in environment over the last 800,000 years from chemical analysis of the EPICA Dome C ice core2010In: Quaternary Science Reviews, ISSN 0277-3791, E-ISSN 1873-457X, Vol. 29, no 1-2, p. 285-295Article in journal (Refereed)
    Abstract [en]

    The EPICA ice core from Dome C extends 3259 m in depth, and encompasses 800 ka of datable and sequential ice. Numerous chemical species have been measured along the length of the cores. Here we concentrate on interpreting the main low-resolution patterns of major ions. We extend the published record for non-sea-salt calcium, sea-salt sodium and non-sea-salt sulfate flux to 800 ka. The non-sea-salt calcium record confirms that terrestrial dust originating from South America closely mirrored Antarctic climate, both at orbital and millennial timescales. A major cause of the main trends is most likely climate in southern South America, which could be sensitive to subtle changes in atmospheric circulation. Sea-salt sodium also follows temperature, but With a threshold at low temperature. We re-examine the use of sodium as a sea ice proxy, concluding that it is probably reflecting extent, with high salt concentrations reflecting larger ice extents. With this interpretation, the sodium flux record indicates low ice extent operating as an amplifier in warm interglacials. Non-sea-salt sulfate flux is almost constant along the core, confirming the lack of change in marine productivity (for sulfur-producing organisms) in the areas of the Southern Ocean contributing to the flux at Dome C. For the first time we also present long records of reversible species such as nitrate and chloride, and show that the pattern of post-depositional losses described for shallower ice is maintained in older ice. It appears possible to use these concentrations to constrain snow accumulation rates in interglacial ice at this site, and the results suggest a possible correction to accumulation rates in one early interglacial. Taken together the chemistry records offer a number of constraints on the way the Earth system combined to give the major climate fluctuations of the late Quaternary period.

1 - 18 of 18
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