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Published: 10 December 2022
Last updated: 28 January 2023

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1

Pasteur, Elizabeth. "Biogenic sulphur in Antarctic ice cores." Thesis, University of East Anglia, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.318083.

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2

Conway, T. M. "Solubility and bioavailability of iron from dust in Antarctic ice cores." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.597913.

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The Iron Hypothesis suggests that an increased flux of aerosol iron to the Southern Ocean (and other Fe limited regions of the ocean) during glacial intervals may have stimulated primary productivity. This could have resulted in more storage of carbon in the deep ocean and less in the atmosphere. This study was designed to increase our understanding of the iron hypothesis, by increasing constraints on several aspects of the theory. The results show that the mean aerosol Fe solubility at Dome C during the Last Glacial Maximum was relatively high (10%), compared to the solubility of typical crustal materials and assumptions used in previous models of ocean biogeochemistry, but also very variable (1-42%). Measurements of other major elemental concentrations in ice were made to assess their suitability for use as proxies of Fe concentrations in dust and to discriminate changes in dust composition and mineralogy. This study shows that ice core Ca concentration is a good proxy for total, but not seawater-soluble, aerosol Fe concentration. These results suggest that atmospheric dust which was deposited at Dome C was enriched in K-rich clay minerals over the Patagonian source regions. New methods were developed to sublimate ice-core material to extract dry dust for use in biological incubation experiments. This study has been the first to incubate siliceous Antarctic phytoplankton (diatoms) with dust of last glacial maximum age, extracted from the EDC ice core, under realistic conditions. The results show that dissolved Fe released from dust had a direct fertilising effect.
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3

Dixon, Daniel A. "A 200-year Sulfate Record from 16 Antarctic Ice Cores and Associations with Southern Ocean Sea Ice Extent." Fogler Library, University of Maine, 2004. http://www.library.umaine.edu/theses/pdf/DixonDA2004.pdf.

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4

Williams, Jessica. "Toward a Better Understanding of Recent Warming of the Central West Antarctic Ice Sheet from Shallow Firn Cores." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3939.

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Previous studies have shown significant warming through the 1990s in the West Antarctic Ice Sheet (WAIS); but the records used in those studies end in early 2000, preventing trend analysis into the latest decade. Fourteen new snowpits and firn cores were collected in 2010 and 2011, which have been combined with previous cores to extend the isotopic records over WAIS. Significance of these isotopic patterns across WAIS was determined and is used to re-evaluate the warming of the West Antarctic interior over recent decades. We find that isotopic records longer than 50 years are needed to assess climate trends due to decadal variability. When assessed over periods greater than 50 years, there is a statistically significant warming trend over central WAIS. However, the isotopes in the 2000s are anomalously low in the isotopic records, which challenge the recent suggestion that the warming trend is accelerating. We attribute the isotopic low over the most recent decade to the coupling effect of anomalously low temperatures over central WAIS and associated increase in sea ice in the adjacent seas. This work strongly indicates that decadal variability and likely climate trends are both driven, at least in part, by atmospheric variability in the tropics as well as at high latitudes.
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5

Massam, Ashleigh. "Modelling the age-depth and temperature profiles of deep ice cores from the Antarctic Peninsula and the Weddell Sea region." Thesis, Durham University, 2017. http://etheses.dur.ac.uk/12678/.

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Three deep ice cores, obtained from Fletcher Promontory, Berkner Island, and James Ross Island across the Antarctic Peninsula (AP) and Weddell Sea region, preserve a climate record that can yield important information on the region. However, before this information can be interpreted, an accurate age-depth profile is required. This study seeks to develop optimal age-depth profiles for the three deep ice cores. The first branch of work is a modelling synthesis of the different physical relationships that reconstruct past surface temperature, accumulation, and the subsequent compaction of accumulation to annual layer thickness (thinning) at an ice-core site. From these relationships, one can estimate an age-depth profile for an ice core. The second half of the study includes the results of chemical analysis on the three deep ice cores. The results of these analyses yield observational data that has been used to assess the accuracy and reliability of the modelling results presented in this part of the study. The OptAcc age-depth model has been developed through this study; it uses an inverse approach to anchor reconstructed profiles of accumulation, thinning, and annual layer thickness profiles to observational data preserved in the ice core. This has been done for the deep ice cores from the AP and Weddell Sea region. Interpretation of the results from this study provides information on the climate history of the region. In particular, the OptAcc model suggests that the coastal proximity of each ice core site leads to high inter-annual variability in accumulation that cannot be reconstructed using standard mathematical relationships. Additionally, an accurate surface temperature, accumulation and age-depth reconstruction for each ice-core site over the Holocene period suggests that an increase in the mean annual surface temperature of 1-3 K is sufficient to lead to significant deglaciation of the AP and Weddell Sea region.
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6

Criscitiello, Alison Sara. "Amundsen Sea sea-ice variability, atmospheric circulation, and spatial variations in snow isotopic composition from new West Antarctic firn cores." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87517.

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Thesis: Ph. D., Joint Program in Oceanography/Applied Ocean Science and Engineering (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2014.
Page 242 blank. Cataloged from PDF version of thesis.
Includes bibliographical references.
Recent work has documented dramatic changes in the West Antarctic Ice Sheet (WAIS) over the past 30 years (e.g., mass loss, glacier acceleration, surface warming) due largely to the influence of the marine environment. WAIS is particularly vulnerable to large-scale atmospheric dynamics that remotely influence the transport of marine aerosols to the ice sheet. Understanding seasonal- to decadal-scale changes in the marine influence on WAIS (particularly sea-ice concentration) is vital to our ability to predict future change. In this thesis, I develop tools that enable us to reconstruct the source and transport variability of marine aerosols to West Antarctica in the past. I validate new firn-core sea-ice proxies over the satellite era; results indicate that firn-core glaciochemical records from this dynamic region may provide a proxy for reconstructing Amundsen Sea and Pine Island Bay polynya variability prior to the satellite era. I next investigate the remote influence of tropical Pacific variability on marine aerosol transport to West Antarctica. Results illustrate that both source and transport of marine aerosols to West Antarctica are controlled by remote atmospheric forcing, linking local dynamics (e.g., katabatic winds) with large-scale teleconnections to the tropics (e.g., Rossby waves). Oxygen isotope records allow me to further investigate the relationship between West Antarctic firn-core records and temperature, precipitation origin, sea-ice variability, and large-scale atmospheric circulation. I show that the tropical Pacific remotely influences the source and transport of the isotopic signal to the coastal ice sheet. The regional firm-core array reveals a spatially varying response to remote tropical Pacific forcing. Finally, I investigate longer-term (-200 year) ocean and ice-sheet changes using the methods and results gleaned from the previous work. I utilize sea-ice proxies to reconstruct long-term changes in sea-ice and polynya variability in the Amundsen Sea, and show that the tropics remotely influence West Antarctica over decadal timescales. This thesis utilizes some of the highest-resolution, most coastal records in the region to date, and provides some of the first analyses of the seasonal- to decadal-scale controls on source and transport of marine aerosols to West Antarctica.
by Alison Sara Criscitiello.
Ph. D.
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7

Harder, Susan. "Deposition of sulfate aerosol and isotopes of beryllium to the antarctic snow surface and implications for ice cores and climate /." Thesis, Connect to this title online; UW restricted, 1996. http://hdl.handle.net/1773/11544.

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8

Bazin, Lucie. "Analyse de l’air piégé dans les carottes de glace de Dôme C et Talos Dôme pour mieux contraindre le rôle du forçage orbital et des gaz à effet de serre dans les variations glaciaire-interglaciaire." Thesis, Versailles-St Quentin en Yvelines, 2015. http://www.theses.fr/2015VERS013V/document.

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Afin d’étudier les variations climatiques enregistrées par les carottes de glace, il est nécessaire d’avoir des datations précises à la fois pour les phases gaz et glace. Le but de ce travail de thèse a été d’améliorer les chronologies des carottes de glace, couvrant les derniers 800 000 ans, au travers de nouvelles mesures de la composition isotopique de l’air (δ15N, δ18Oatm et δO2/N2) piégé dans la glace d’EPICA Dôme C (EDC) et de l’utilisation de l’outil de datation "Datice". Le premier résultat important de cette thèse a été la production de la chronologie cohérente pour les carottes de glace ("Antarctic Ice Core Chronology", AICC2012) pour EDC, Vostok, EPICA Droning Maud Land (EDML), TALos Dôme ICE core (TALDICE) et NorthGRIP. Sur cette nouvelle chronologie la théorie du see-saw bipolaire reste valable. AICC2012 donne un âge pour la Terminaison II en accord avec les autres archives climatiques. De plus, les durées des périodes interglaciaires restent inchangées par rapport à la chronologie EDC3. Lors de la construction d’AICC2012 nous avons mis en évidence plusieurs points nécessitant des améliorations. Nous avons donc procédé à l’amélioration de Datice dans le but d’intégrer correctement les contraintes issues du comptage des couches annuelles et leurs erreurs. Ces améliorations conduisent à des chronologies cohérentes tout en respectant les hypothèses sous-jacentes à Datice. Nous proposons aussi une nouvelle formulation de l’erreur associée à la fonction d’amincissement à partir de l’analyse des propriétés mécaniques de la glace dans le cas d’EDC. Pour finir, les nouvelles mesures du δO2/N2 et du δ18Oatm effectuées sur de la glace bien conservée d’EDC nous ont permis de définir de nouvelles contraintes d’âge. La comparaison de ces traceurs mesurés à Vostok, EDC et Dôme F sur le MIS 5 a permis de mettre en évidence une possible influence de paramètres climatiques locaux sur le δO2/N2. L’analyse du retard entre le δ18Oatm et la précession sur les derniers 800 ka montre des variations de ce dernier. Nous suggérons que ce retard est augmenté par l’occurence d’évènements de Heinrich à certaines périodes. Les résultats de cette thèse sont à prendre en compte pour le prochain exercice de datation cohérente pour les carottes de glace
In order to study the climate variations recorded by ice cores, it is necessary to have precise chronologies for the ice and gas phases. The aim of this work has been to improve ice cores chronologies, covering the last 800 000 years, through new measurements of the isotopic composition of the air δ15N, δ18Oatm et δO2/N2) trapped in EPICA Dome C (EDC) ice core and the use of the Datice dating tool.The first important result of this PhD has been the production of the Antarctic Ice Core Chronology (AICC2012), common for EDC, Vostok, EPICA Droning Maud Land (EDML), TALos Dome ICE core (TALDICE) and NorthGRIP ice cores. The bipolar see-saw theory is still valid on the new chronology. The AICC2012 chronology gives an age for Termination II in good agreement with other climate archives. Moreover, the duration of interglacial periods is unchanged compared to EDC3. While building the AICC2012 chronology, we have pointed out several limitations. Since then, we have improved Datice in order to correctly integrate constraints deduced from layer counting and their associated uncertainties. These improvements permit to build coherent chronologies respecting the underlying hypotheses of Datice. Moreover, we propose a new parameterization of the uncertainty associated with the background thinning function based on ice mechanical properties of EDC ice core. Finally, we were able to deduce new age constraints thanks to the new measurements of δO2/N2 and δ18Oatm performed on well-conserved ice from EDC. A multi-proxy comparison of Vostok, EDC and Dome F ice cores over MIS 5 has highlighted a possible influence of local climatic parameters on δO2/N2. The analysis of the delay between δ18Oatm and precession shows some variability over the last 800 ka. We propose that the delay between δ18Oatm and precession is increased during periods associated with Heinrich events. The results obtained during this PhD should be used for the next ice core coherent chronology
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9

Kaspari, Susan. "Climate Variability in West Antarctica Derived from Accumulation and Marine Aerosol Records from ITASE Firn/Ice Cores." Fogler Library, University of Maine, 2004. http://www.library.umaine.edu/theses/pdf/KaspariS2004.pdf.

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10

Carlos, Franciéle Schwanck. "Variabilidade química e climática no registro do Testemunho de Gelo Mount Johns – Antártica." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2016. http://hdl.handle.net/10183/139089.

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Esta tese interpreta o registro ambiental de um testemunho de gelo antártico pela análise de elementostraço. Esse testemunho de gelo, daqui em diante chamado Mount Johns (MJ), foi coletado no manto de gelo da Antártica Ocidental (79°55’28”S e 94°23’18”W; 91,20 m de comprimento) no verão austral de 2008/09. O testemunho foi descontaminado e subamostrado no Climate Change Institute (University of Maine – Maine /EUA). As primeiras 2137 amostras, correspondentes aos 45 m superiores do testemunho, foram analisadas no espectrômetro de massas Element 2 do CCI para 24 elementos-traço (Sr, Cd, Cs, Ba, La, Ce, Pr, Pb, Bi, U, As, Li, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co, Na, Mg e K). Essa parte do testemunho representa 125 anos (1883–2008) de registro, segundo datação relativa baseada na variação sazonal nas concentrações de Na, Sr e S e na identificação dos principais eventos vulcânicos ocorridos no período. A taxa de acumulação média no local de amostragem foi 0,21 m a-1 em eq. H2O no mesmo período de tempo. As concentrações são controladas pelas variações climáticas sazonais (verão/inverno), por mudanças na circulação atmosféricas, por anomalias de temperatura, pela distância de transporte e pelas fontes naturais e antrópicas desses aerossóis. Baseada na análise dos fatores de enriquecimento crustal e marinho e em correlações de Pearson, as concentrações de Al, Ba, Ca, Fe, K, Mg, Mn, Na, S, Sr e Ti são de origem natural. Poeira e solo de fontes continentais, oriundas principalmente de áreas áridas na Austrália, Nova Zelândia e Patagônia, são consideradas importantes fontes de Al, Mg e Ti. Aerossóis marinhos do Pacífico Sul, transportados para o continente antártico pelas massas de ar, são fontes predominantes de Na, Sr, K, S e Ca. Para os elementos Ba, Fe e Mn, tanto fontes crustais como marinhas são significativas. Adicionalmente, Mn e S apresentam um aporte considerável de origem vulcânica (variando de 20–30% na concentração total). Os resultados também mostram enriquecimento significativo nas concentrações de arsênio devido a atividades antrópicas. Foi observado concentrações médias da ordem de 1,92 pg g-1 antes de 1900, aumentando até 7,94 pg g-1 em 1950. Este enriquecimento está diretamente relacionado às emissões da mineração e fundição de metais não-ferrosos na América do Sul, principalmente no Chile. A queda na concentração de arsênio observado no século XXI (concentração média de 1,94 pg g-1 após 1999) é interpretada como uma consequência à introdução de leis ambientais (em 1994) para reduzir emissões desse elemento durante os processos de mineração e fundição de cobre no Chile. O modelo de trajetórias HYSPLIT mostra uma clara variação sazonal no transporte entre os meses de verão/outono e inverno/primavera, onde predomina o transporte de oeste durante o ano todo e um transporte secundário de nordeste durante o verão/outono. As correlações entre as concentrações médias dos elementos-traço estudados e o modelo de reanálises ERA-Interim para o período 1979–2008, indicam que as concentrações de aerossóis marinhos são fortemente influenciadas pelas condições meteorológicas, por exemplo, por anomalias na temperatura da superfície do mar e concentração de gelo marinho.
This thesis interprets the environmental record of an Antarctic ice core by the analysis of trace elements. This ice core, henceforward called Mount Johns (MJ), was collected in the West Antarctica ice sheet (79°55'28"S and 94°23'18"W; 91.20 m long) in the austral summer of 2008/09. The core was decontaminated and subsampled at the Climate Change Institute (CCI, University of Maine - Maine / USA). The first 2137 samples, corresponding to the upper 45 m of the core, were analyzed in the CCI's JRC Element 2 spectrometer for 24 trace elements (Sr, Cd, Cs, Ba, La, Ce, Pr, Pb, Bi, U, As, Li, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co, Na, Mg and K). This part of the core represents a 125 years (1883– 2008) record, according to relative dating based on Na, Sr and S seasonal variations and on the identification of major volcanic events in the period. The mean accumulation rate for the sampling site was 0.21 m-1 in eq. H2O in the same time period. The concentrations are controlled by seasonal climatic changes (summer/winter), by changes in atmospheric circulation, temperature anomalies, the transport distance and the natural and anthropogenic sources of these aerosols. Based on analysis of crustal and marine enrichment factors and Pearson correlations, the Al, Ba, Ca, Fe, K, Mg, Mn, Na, S, Sr and Ti concentrations have natural origin. Dust and soil from continental sources, primarily coming from arid areas in Australia, New Zealand and Patagonia, are considered important sources of Al, Mg and Ti. South Pacific marine aerosols, transported to the Antarctic continent by air masses, are predominant sources of Na, Sr, K, S and Ca. For the elements Ba, Fe and Mn, both crustal and marine sources are significant. In addition, Mn and S show a considerable contribution of volcanic origin (ranging from 20-30% of the total concentration). The results also show significant enrichment in arsenic concentrations due to human activities. Before 1900 the mean concentration was approximately 1.92 pg g-1, rising to 7.94 pg g-1 in 1950. This enrichment is directly related to mining emissions and casting of non-ferrous metals in South America, mainly in Chile. The decrease in the arsenic concentration, observed in the twenty-first century (mean concentration of 1.94 pg g-1 after 1999) is interpreted as a consequence of the introduction of environmental laws (in 1994) to reduce emissions of this element during the cupper mining and smelting in Chile. The HYSPLIT trajectories model show a clear seasonal variation in transport between the summer/autumn all and winter/spring months, where predominates an eastward transport throughout the year and a secondary transport from the northeast during the summer/fall. Correlations between the mean concentrations of the studied trace elements and the ERA-Interim reanalysis models for the 1979-2008 period indicate that marine aerosols concentrations are heavily influenced by weather conditions, for example, by sea surface temperature and sea ice concentration anomalies.
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11

Gura, Colby J. "Characterization of Organisms in Vostok (Antarctica) Glacial, Basal, and Accretion Ice." Bowling Green State University / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1566486484767222.

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12

Burgener, Landon Kelly. "Temporal trends in West Antarctic accumulation rates: evidence from observed and simulated records." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3664.

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Reconstructed snow accumulation rate observations from five new firn cores show a statistically significant negative trend in accumulation rates over the past four decades across the central West Antarctic ice sheet. A negative temporal trend in accumulation is unexpected in light of rising surface temperatures and simulations run by GCMs. Both the magnitude of the mean accumulation rates and the range of interannual variability observed in the new records compares favorably to older records, suggesting that the new accumulation rate records may serve as a regional proxy for recent temporal trends in West Antarctic accumulation rates. The observed negative trend is likely the result of Southern Hemisphere high-latitude internal atmospheric dynamics, dominated by changes in the austral fall season. The well-documented positive trend in the Southern Annular Mode causes a low pressure center to form over the Amundsen Sea, which in turn produces lower accumulation rates across the western portion of the West Antarctic ice sheet. The new accumulation rate records are compared to several models/reanalyses to test the skill of simulated accumulation rate predictions. While the models/reanalyses and the new observations agree well in both mean and variability, the simulated records do not capture the full negative trend observed in the reconstructed records.
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13

Carpenter, McLean Kent. "West Antarctic Surface Mass Balance: Do Synoptic Scale Modes of Climate Contribute to Observed Variability?" BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4382.

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Western Antarctica has been experiencing significant warming for at least the past fifty years. While higher Net Surface Mass Balance (SMB) over West Antarctica during this period of warming is expected, SMB reconstructions from ice cores reveal a more complex pattern during the period of warming. The mechanisms giving rise to SMB variability over the West Antarctic Ice Sheet (WAIS) are not well understood due to lack of instrumental data. The Southern Annular Mode (SAM) and El Niño Southern Oscillation (ENSO) are believed to contribute to WAIS SMB variability but the assumption has not been rigorously tested. SMB during years where SAM and ENSO are in extreme phases is compared to average SMB from the period 1979-2010. Additionally, atmospheric circulation anomalies are used to assess what circulation patterns accompany extreme modes of climate during the same period. The results suggest that significantly lower SMB occurs when SAM is in an extremely positive phase or ENSO is in an extremely negative phase. Additionally, atmospheric circulation anomalies show that certain circulation patterns accompany extreme modes of climate, which contribute to SMB variability over the WAIS. Ultimately, the location of low and high pressure cells is the best predictor for extreme accumulation events over the WAIS. These results are verified by assessing observed net SMB trends from a network of firn cores located from the central WAIS. Seven new firn cores are added to improve the spatial network of regional net SMB measurements. Reconstructed net SMB is calculated from new firn core records, and compared to the existing cores. The new suite of preliminary firn core records show the same significant decreasing trend that is observed in existing cores. This represents a negative region-wide SMB trend that is likely in part due to trends in SAM and ENSO.
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14

Goodwin, Bradley Patrick. "Recent Environmental Changes on the Antarctic Peninsula as Recorded in an ice core from the Bruce Plateau." The Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1373468400.

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15

Münch, Thomas [Verfasser], and Thomas [Akademischer Betreuer] Laepple. "Interpretation of temperature signals from ice cores : insights into the spatial and temporal variability of water isotopes in Antarctica / Thomas Münch ; Betreuer: Thomas Laepple." Potsdam : Universität Potsdam, 2018. http://d-nb.info/1218403837/34.

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16

Philippe, Morgane. "Reconstruction of the density profile, surface mass balance history and vertical strain profile on the divide of the Derwael Ice Rise in coastal Dronning Maud Land, East Antarctica." Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/254506.

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Antarctic mass balance is mainly controlled by surface mass balance (SMB, i.e. the net effect of precipitations at the surface of the ice sheet) and ice discharge at its margins, mostly through ice shelves. These floating ice bodies made from ice flowing from the continent to the ocean are buttressed by ice rises (elevation of the sea floor on which ice shelf re-grounds) such as the Derwael Ice Rise (DIR) in Dronning Maud Land (DML). In addition to this role important to consider in the future contribution of Antarctica to sea level rise, ice rises are also “climate dipsticks” helping to reconstruct the climate of the past centuries to millennia at high resolution. Due to their coastal location, they witness the changes happening there more rapidly than inland. Furthermore, their internal stratigraphy forms arches that allow to assess their stability, to date their own formation and therefore, in some cases, to constrain the past extension of the ice sheet at the scale of several millennia. As part of the IceCon project :Constraining ice mass changes in Antarctica, this thesis aimed to drill a 120 m ice core (named IC12 for the IceCon project, 2012) at the divide of the DIR and perform physico-chemical analyses to study its density and its internal annual layering with the aim of reconstructing SMB of the last two centuries. We also recorded a virtual image of the borehole using an optical televiewer (OPTV) to assess the ability of this instrument to reconstruct a density profile and measure vertical strain rates when the logging is repeated in the same borehole after a sufficient period of time (here, 2 years).The results show a general increase in snow accumulation rates (SMB) of 30-40% during the 20th century, particularly marked during the last 20-50 years. SMB variability is governed to a large extent by atmospheric circulation and to a lesser extent by variations in sea ice cover. The vertical velocity profile measured from repeat borehole OPTV was applied to refine SMB correction and the results fall in the error range of the corrections made using a model previously developed to study the DIR’s stability. This thesis also contributed to characterizing the spatial variability of SMB across the DIR by dating internal reflection horizons (IRHs), former surfaces of the DIR buried under subsequent snow layers and detected using radio-echo-sounding, and by measuring the density profile of IC12. SMB is found to be 2.5 times higher on the upwind slope than on the downwind slope due to the orographic effect. This pattern is regularly observed on ice rises in DML and stresses the importance of adopting a sufficient spatial resolution (5 km) in climate models.Finally, the technical developments allowing to rapidly reconstruct a density profile from the OPTV image of a borehole contributed to improving our knowledge of two features of Antarctic ice shelves, namely melt ponds, influencing surface mass balance and subglacial channels, influencing basal mass balance. Specifically, the results show that density is 5 % higher in surface trenches associated with subglacial channels, and that ice below melt ponds can reach the density of bubble-free ice due to melting and refreezing processes, with implications on ice shelf viscosity.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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17

Philippe, Morgane. "Reconstruction of the density profile, surface mass balance history and vertical strain profile on the divide of the Derwael Ice Rise in coastal Dronning Maud Land, East Antarctica." Doctoral thesis, Universite Libre de Bruxelles, 2017. https://dipot.ulb.ac.be/dspace/bitstream/2013/254506/7/Appendix.pdf.

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Antarctic mass balance is mainly controlled by surface mass balance (SMB, i.e. the net effect of precipitations at the surface of the ice sheet) and ice discharge at its margins, mostly through ice shelves. These floating ice bodies made from ice flowing from the continent to the ocean are buttressed by ice rises (elevation of the sea floor on which ice shelf re-grounds) such as the Derwael Ice Rise (DIR) in Dronning Maud Land (DML). In addition to this role important to consider in the future contribution of Antarctica to sea level rise, ice rises are also “climate dipsticks” helping to reconstruct the climate of the past centuries to millennia at high resolution. Due to their coastal location, they witness the changes happening there more rapidly than inland. Furthermore, their internal stratigraphy forms arches that allow to assess their stability, to date their own formation and therefore, in some cases, to constrain the past extension of the ice sheet at the scale of several millennia. As part of the IceCon project :Constraining ice mass changes in Antarctica, this thesis aimed to drill a 120 m ice core (named IC12 for the IceCon project, 2012) at the divide of the DIR and perform physico-chemical analyses to study its density and its internal annual layering with the aim of reconstructing SMB of the last two centuries. We also recorded a virtual image of the borehole using an optical televiewer (OPTV) to assess the ability of this instrument to reconstruct a density profile and measure vertical strain rates when the logging is repeated in the same borehole after a sufficient period of time (here, 2 years).The results show a general increase in snow accumulation rates (SMB) of 30-40% during the 20th century, particularly marked during the last 20-50 years. SMB variability is governed to a large extent by atmospheric circulation and to a lesser extent by variations in sea ice cover. The vertical velocity profile measured from repeat borehole OPTV was applied to refine SMB correction and the results fall in the error range of the corrections made using a model previously developed to study the DIR’s stability. This thesis also contributed to characterizing the spatial variability of SMB across the DIR by dating internal reflection horizons (IRHs), former surfaces of the DIR buried under subsequent snow layers and detected using radio-echo-sounding, and by measuring the density profile of IC12. SMB is found to be 2.5 times higher on the upwind slope than on the downwind slope due to the orographic effect. This pattern is regularly observed on ice rises in DML and stresses the importance of adopting a sufficient spatial resolution (5 km) in climate models.Finally, the technical developments allowing to rapidly reconstruct a density profile from the OPTV image of a borehole contributed to improving our knowledge of two features of Antarctic ice shelves, namely melt ponds, influencing surface mass balance and subglacial channels, influencing basal mass balance. Specifically, the results show that density is 5 % higher in surface trenches associated with subglacial channels, and that ice below melt ponds can reach the density of bubble-free ice due to melting and refreezing processes, with implications on ice shelf viscosity.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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18

Vallelonga, Paul Travis. "Measurement of Lead Isotopes in Snow and Ice from Law Dome and other sites in Antarctica to characterize the Lead and seek evidence of its origin." Thesis, Curtin University, 2002. http://hdl.handle.net/20.500.11937/2580.

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Human activities such as mining and smelting of lead (Pb) ores and combustion of alkyllead additives in gasoline have resulted in extensive global Pb pollution. Since the late 1960's studies of polar ice and snow have been undertaken to evaluate the extent of anthropogenic Pb emissions in recent times as well as to investigate changes in anthropogenic Pb emissions in the more distant past. The polar ice sheets have been used to investigate Pb pollution as they offer a long-term record of human activity located far from pollution sources and sample aerosol emissions on a hemispheric scale. Lead isotopes have been previously used to identify sources of Pb in polar snow and ice, while new evaluations of Pb isotopic compositions in aerosols and Pb ore bodies allow more thorough evaluations of anthropogenic Pb emissions. Lead isotopic compositions and Pb and Barium (Ba) concentrations have been measured in snow and ice core samples from Law Dome, East Antarctica, to produce a detailed pollution history between 1530 AD and 1989 AD. Such a record has been produced to evaluate changes in anthropogenic Pb emission levels and sources over the past 500 years, to determine when industrial (anthropogenic) activities first began to influence Antarctica and also to investigate natural Pb fluxes to Antarctica. Additional samples were also collected from Law Dome snow and ice cores to respectively investigate seasonal variations in Pb and Ba deposition, and the influence of the 1815 AD volcanic eruption of Tambora, Indonesia. All samples were measured by thermal ionisation mass spectrometry, for which techniques were developed to reliably analyse Pb isotopic compositions in Antarctic samples containing sub-picogram per gram concentrations of Pb.Particular attention was given to the quantity of Pb added to the samples during the decontamination and sample storage stages of the sample preparation process. These stages, including the use of a stainless steel chisel for the decontamination, contributed ~5.2 pg to the total sample analysed, amounting to a concentration increase of ~13 fg g-1. In comparison, the mass spectrometer ion source contributed typically 89 +/- 19 fg to the blank, however its influence depended upon the amount of Pb available for analysis and so had the greatest impact when small volumes of samples with a very low concentration were analysed. As a consequence of these careful investigations of the Pb blank contributions to the samples, the corrections made to the Pb isotopic ratios and concentrations measured are smaller than previously reported evaluations of Pb in Antarctica by thermal ionisation mass spectrometry. The data indicate that East Antarctica was relatively pristine until -1884 AD, after which the first influence of anthropogenic Pb in Law Dome is observed. "Natural", pre-industrial, background concentrations of Pb and Ba were - 0.4 pg/g and - 1.3 pg/g, respectively, with Pb isotopic compositions within the range 206Pb/207Pb = 1.20 - 1.25 and 208Pb/207Pb = 2.46 - 2.50 and an average rock and soil dust Pb contribution of 8-12%. A major pollution event was observed at Law Dome between 1884 and 1908 AD, elevating the Pb concentration fourfold and changing 206Pb/207Pb ratios in the ice to ~1.12. Based on Pb isotopic systematics and Pb emissions statistics, this was attributed to Pb mined at Broken Hill and smelted at Broken Hill and Port Pirie, Australia.Anthropogenic Pb inputs to Law Dome were most significant from ~1900 to 1910 and from ~1960 to 1980. During the 20th century, Ba concentrations were consistently higher than "natural" levels. This was attributed to increased dust production, suggesting the influence of climate change and/or changes in land coverage with vegetation. Law Dome ice dated from 1814 AD to 1819 AD was analysed for Pb isotopes and Pb, Ba and Bismuth (Bi) concentrations to investigate the influence of the 1815 AD volcanic eruption of Tambora, Indonesia. The presence of volcanic debris in the core samples was observed from late-1816 AD to 1818 AD as an increase in sulphate concentrations and electrical conductivity of the ice. Barium concentrations were approximately three times higher than background levels from mid-1816 to mid1818, consistent with increased atmospheric loading of rock and soil dust, while enhanced Pb/Ba and Bi/Ba ratios, associated with deposition of volcanic debris, were observed at mid-1814 and from early-1817 to mid-1818. From the results, it appeared likely that Pb emitted from Tambora was removed from the atmosphere within the 1.6 year period required to transport aerosols to Antarctica. Increased Pb and Bi concentrations observed in Law Dome ice ~1818 AD were attributed to either increased heavy metal emissions from Mount Erebus, or increased fluxes of heavy metals to the Antarctic ice sheet resulting from climate and meteorological modifications following the Tambora eruption.A non-continuous series of Law Dome snow core samples dating from 1980 to 9185 AD were analysed to investigate seasonal variations in the deposition of Pb and Ba. It was found that Pb and Ba at Law Dome do exhibit seasonal variations in deposition, with higher concentrations of Pb and Ba usually observed during Summer and lower concentrations of Pb and Ba usually observed during the Autumn and Spring seasons. At Law Dome, broad patterns of seasonal Pb and Ba deposition are evident however these appear to be punctuated by short-term deposition events or may even be composed of a continuum of short-term deposition events. This variability suggests that complex meteorological systems are responsible for the transport of Pb and Ba to Law Dome, and probably Antarctica in general.
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19

Thoen, Isaías Ullmann. "Conteúdo iônico em testemunho de firn/gelo do monte Johns Antártica Ocidental: 1882–2008 A.D." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2017. http://hdl.handle.net/10183/156556.

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Esta dissertação investiga o registro de conteúdo iônico do testemunho de gelo monte Johns (79°55'28"S; 94°23'18"O) obtido na Antártica Ocidental, contribuindo para o adensamento espacial de informações glacioquímicas empregadas em estudos paleoclimáticos. As concentrações de Na+ (16,6 ± 28,2 μg L-1), K+ (1,3 ± 3,7 μg L-1), Mg2+ (3,7 ± 3,7 μg L-1), Ca2+ (5,4 ± 3,4 μg L-1), Cl- (33,3 ± 43,7 μg L-1), SO42- (25,9 ± 17,7 μg L-1), NO3- (50,8 ± 18,5 μg L-1) e H3CSO3- (7,1 ± 5,4 μg L-1) foram determinadas por cromatografia iônica em 2.164 amostras para o período 1882–2008. A variabilidade sazonal de NO3- e, especialmente do nssSO42-, em antifase com Na+, possibilitou a datação pela contagem de ciclos anuais ao longo do período estudado. A identificação dos sinais vulcânicos do Krakatoa (1883), Agung (1963) e Pinatubo/Hudson (1991) foi usada para determinar horizontes de referência (datação absoluta). Eventos de aporte significativo de aerossóis foram identificados e agrupados considerando o conteúdo iônico, proveniência e estação do ano. A avaliação da proveniência dos íons e do balanço iônico mostra a origem da carga iônica: 36% é oriunda de aerossóis de sal marinho, 13% de poeira mineral, 17% de atividade biogênica marinha e 34% de produtos da reatividade química na atmosfera. É observada uma leve redução nas concentrações de Mg2+ (-0,04 μg L-1 ano-1) e K+ (-0,01 μg L-1 ano-1), e mais forte para NO3- (-0,17 μg L-1 ano-1), no período 1909–2008. A média anual da acumulação líquida de neve foi 0,21 ± 0,04 m eq. H2O no período 1882–2008 sem apresentar tendência significante. A acumulação mostra alta correspondência com dados anuais de reanálise climática, com coeficiente de correlação cruzada de +0,42 (α < 0,05) para o período 1979–2008.
This dissertation investigates the ionic content record of the mount Johns ice core (79°55'28"S; 94°23'18"W) recovered from the West Antarctica, contributing to the spatial densification of glaciochemical information used in paleoclimatic studies. The concentrations of Na+ (16.6 ± 28.2 μg L-1), K+ (1.3 ± 3.7 μg L-1), Mg2+ (3.7 ± 3.7 μg L-1), Ca2+ (5.4 ± 3.4 μg L-1), Cl- (33.3 ± 43.7 μg L-1), SO42- (25.9 ± 17.7 μg L-1), NO3- (50.8 ± 18.5 μg L-1) e H3CSO3- (7.1 ± 5.4 μg L-1) were determined by ion chromatography on 2,164 samples for the period 1882–2008. The NO3- seasonal variability and, especially, of the nssSO42- in antiphase with the Na+, allowed the counting of annual cycles over the studied period. The identification of Krakatau (1883), Agung (1963) and Pinatubo / Hudson (1991) volcanic signals was used to determine reference horizons (absolute dating). Significant aerosols events were identified and grouped considering the ionic content, provenance and season of the year. The evaluation of the ions provenance and of the ionic balance points to ionic content origin: 36% come from sea salt aerosols, 13% from mineral dust, 17% originate from marine biogenic activity and 34% are chemical reactivity products in the atmosphere. It is observed a slight reduction in the Mg2+ (-0.04 μg L-1 y-1) and K+ (-0.01 μg L-1 y-1) concentrations, and stronger in the NO3- (-0.17 μg L-1 y-1), during the 1909–2008 period. The annual mean net accumulation rate averaged 0.21 ± 0.04 m w.e. y-1 in the period 1882–2008 did not show any significant trend and shows high correspondence with climatic reanalysis data in years with data overlap, with a cross-correlation coefficient of +0.42 (α < 0.05) for the period 1979–2008.
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20

Carlos, Franciéle Schwanck. "Determinação de elementos traços em testemunho de firn Antártico usando espectrometria de massa." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2012. http://hdl.handle.net/10183/70036.

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O testemunho de firn IC-6 de 35,06 m de comprimento foi coletado no manto de gelo antártico (81°03’10,1”S e 79°50’09,1”W; 750 m de altitude) no verão austral de 2004/05. Este testemunho foi subamostrado usando um sistema de fusão contínua desenvolvido pela equipe do Climate Change Institute (University of Maine – Maine /EUA) em sala limpa (CLASSE 100). As 1380 amostras geradas foram analisadas em baixa, média e alta resolução no espectrômetro de massas Element 2 do CCI para 24 elementos traços (Sr, Cd, Cs, Ba, La, Ce, Pr, Pb, Bi, U, As, Li, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co, Na, Mg e K). O testemunho representa 68 anos (1934 – 2002) de registro, segundo datação relativa baseada na variação sazonal nas concentrações dos elementos Na, Mg, Sr e Ca e dos íons Cl-, Na+ e Mg2+. A taxa de acumulação média para o local de amostragem é calculada em 0,30 m a-1 em Eq. H2O. As concentrações medidas foram consideradas baixas, dentro do esperado para o continente antártico e são similares a de outros estudos. As concentrações são controladas pelas variações climáticas sazonais (verão/inverno), pela distância de transporte e pelas fontes naturais e antrópicas desses aerossóis. Contribuições naturais de poeira continental e solo, oriundas principalmente da região de Patriot Hills, são as principais fontes para os elementos césio, bário, alumínio, titânio, vanádio, cromo, ferro, cobalto, manganês e terras raras. Os aerossóis marinhos, oriundos da superfície da cobertura de gelo marinho e transportados pelas massas de ar são fontes importantes de sódio, magnésio, estrôncio e enxofre. Os elementos lítio, cálcio e potássio apresentaram aportes consideráveis tanto de poeira continental como de aerossóis marinhos. Emissões vulcânicas globais e regionais (Monte Erebus e Ilha Deception) são consideradas importantes fontes de elementos traços. Elementos como vanádio, cromo, manganês, cobalto, bismuto, arsênio, cádmio e chumbo apresentaram uma significativa contribuição dessas fontes, variando desde 20% (chumbo e manganês) até 70% (cádmio e bismuto). Os fluxos de deposição natural de chumbo, cádmio, bismuto e arsênio, representam apenas uma pequena fração do total depositado na neve. Para esses elementos, as atividades antrópicas constituem o principal fator responsável por sua mobilização e transporte.
This dissertation examines a 35.06 m long firn core (IC-6) obtained in the Austral summer of 2004/2005 in the West Antarctic Sheet (at 81°03’10.1”S, 79°50’09.1”W; 750 m above sea level). This core was subsampled using a continuous melting system at the Climate Change Institute (CCI, University of Maine, Orono, Maine, USA) under a Class 100 room conditions. At CCI, 1380 samples went through an Element 2 mass spectrometer to determine (at low, middle and high resolutions) the concentration of 24 trace elements (Sr, Cd, Cs, Ba, La, Ce, Pr, Pb, Bi, U, As, Li, Al, S, Ca, Ti, V, Cr, Mn, Fe, Co, Na, Mg e K). The core records 38 years (1934 – 2002) of snow accumulation, as dated by seasonal variations of Na, Mg, Sr e Ca elements and Cl-, Na+ e Mg2+ ionic concentrations. The calculated mean annual accumulation is 0.30 m yr-1 (in H2O equivalent). Their mean concentrations are low and are similar to the ones found in other Antarctic ice core studies. Trace concentrations are controlled by seasonal variations (summer/winter), transport distance and by natural and anthropogenic sources. Cesium, barium, aluminium, titanium, vanadium, chrome, iron, cobalt, manganese and rare earths come from continental dust (mainly from the nearby Patriot Hills). Marine aerosols, from the pack ice surface and transported by air masses, are the sources for sodium, magnesium, strontium and sulphur. Both continental dust and marine aerosols contribute to the lithium, calcium and potassium concentrations. Global and regional (Mount Erebus and Deception Island) volcanic emissions are important trace elements sources, such as vanadium, chrome, manganese, cobalt, bismuth, arsenic, cadmium and lead, varying from 20% (lead and manganese) to 70% (cadmium e bismuth). Trace elements as lead, cadmium, bismuth e arsenic from natural sources have a minor contribution in the samples, human activities are thought to be the main cause for their mobilization and transport.
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21

Vallelonga, Paul Travis. "Measurement of Lead Isotopes in Snow and Ice from Law Dome and other sites in Antarctica to characterize the Lead and seek evidence of its origin." Curtin University of Technology, School of Applied Science, 2002. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=14018.

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Human activities such as mining and smelting of lead (Pb) ores and combustion of alkyllead additives in gasoline have resulted in extensive global Pb pollution. Since the late 1960's studies of polar ice and snow have been undertaken to evaluate the extent of anthropogenic Pb emissions in recent times as well as to investigate changes in anthropogenic Pb emissions in the more distant past. The polar ice sheets have been used to investigate Pb pollution as they offer a long-term record of human activity located far from pollution sources and sample aerosol emissions on a hemispheric scale. Lead isotopes have been previously used to identify sources of Pb in polar snow and ice, while new evaluations of Pb isotopic compositions in aerosols and Pb ore bodies allow more thorough evaluations of anthropogenic Pb emissions. Lead isotopic compositions and Pb and Barium (Ba) concentrations have been measured in snow and ice core samples from Law Dome, East Antarctica, to produce a detailed pollution history between 1530 AD and 1989 AD. Such a record has been produced to evaluate changes in anthropogenic Pb emission levels and sources over the past 500 years, to determine when industrial (anthropogenic) activities first began to influence Antarctica and also to investigate natural Pb fluxes to Antarctica. Additional samples were also collected from Law Dome snow and ice cores to respectively investigate seasonal variations in Pb and Ba deposition, and the influence of the 1815 AD volcanic eruption of Tambora, Indonesia. All samples were measured by thermal ionisation mass spectrometry, for which techniques were developed to reliably analyse Pb isotopic compositions in Antarctic samples containing sub-picogram per gram concentrations of Pb.
Particular attention was given to the quantity of Pb added to the samples during the decontamination and sample storage stages of the sample preparation process. These stages, including the use of a stainless steel chisel for the decontamination, contributed ~5.2 pg to the total sample analysed, amounting to a concentration increase of ~13 fg g-1. In comparison, the mass spectrometer ion source contributed typically 89 +/- 19 fg to the blank, however its influence depended upon the amount of Pb available for analysis and so had the greatest impact when small volumes of samples with a very low concentration were analysed. As a consequence of these careful investigations of the Pb blank contributions to the samples, the corrections made to the Pb isotopic ratios and concentrations measured are smaller than previously reported evaluations of Pb in Antarctica by thermal ionisation mass spectrometry. The data indicate that East Antarctica was relatively pristine until -1884 AD, after which the first influence of anthropogenic Pb in Law Dome is observed. "Natural", pre-industrial, background concentrations of Pb and Ba were - 0.4 pg/g and - 1.3 pg/g, respectively, with Pb isotopic compositions within the range 206Pb/207Pb = 1.20 - 1.25 and 208Pb/207Pb = 2.46 - 2.50 and an average rock and soil dust Pb contribution of 8-12%. A major pollution event was observed at Law Dome between 1884 and 1908 AD, elevating the Pb concentration fourfold and changing 206Pb/207Pb ratios in the ice to ~1.12. Based on Pb isotopic systematics and Pb emissions statistics, this was attributed to Pb mined at Broken Hill and smelted at Broken Hill and Port Pirie, Australia.
Anthropogenic Pb inputs to Law Dome were most significant from ~1900 to 1910 and from ~1960 to 1980. During the 20th century, Ba concentrations were consistently higher than "natural" levels. This was attributed to increased dust production, suggesting the influence of climate change and/or changes in land coverage with vegetation. Law Dome ice dated from 1814 AD to 1819 AD was analysed for Pb isotopes and Pb, Ba and Bismuth (Bi) concentrations to investigate the influence of the 1815 AD volcanic eruption of Tambora, Indonesia. The presence of volcanic debris in the core samples was observed from late-1816 AD to 1818 AD as an increase in sulphate concentrations and electrical conductivity of the ice. Barium concentrations were approximately three times higher than background levels from mid-1816 to mid1818, consistent with increased atmospheric loading of rock and soil dust, while enhanced Pb/Ba and Bi/Ba ratios, associated with deposition of volcanic debris, were observed at mid-1814 and from early-1817 to mid-1818. From the results, it appeared likely that Pb emitted from Tambora was removed from the atmosphere within the 1.6 year period required to transport aerosols to Antarctica. Increased Pb and Bi concentrations observed in Law Dome ice ~1818 AD were attributed to either increased heavy metal emissions from Mount Erebus, or increased fluxes of heavy metals to the Antarctic ice sheet resulting from climate and meteorological modifications following the Tambora eruption.
A non-continuous series of Law Dome snow core samples dating from 1980 to 9185 AD were analysed to investigate seasonal variations in the deposition of Pb and Ba. It was found that Pb and Ba at Law Dome do exhibit seasonal variations in deposition, with higher concentrations of Pb and Ba usually observed during Summer and lower concentrations of Pb and Ba usually observed during the Autumn and Spring seasons. At Law Dome, broad patterns of seasonal Pb and Ba deposition are evident however these appear to be punctuated by short-term deposition events or may even be composed of a continuum of short-term deposition events. This variability suggests that complex meteorological systems are responsible for the transport of Pb and Ba to Law Dome, and probably Antarctica in general.
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22

Silva, Marcio Cataldo Gomes da. "Características biogeoquímicas da interação atmosfera criosfera na Antártica ocidental." Universidade do Estado do Rio de Janeiro, 2011. http://www.bdtd.uerj.br/tde_busca/arquivo.php?codArquivo=3339.

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Conselho Nacional de Desenvolvimento Científico e Tecnológico
O manto polar antártico retêm informação paleoclimatologica por entres suas camadas de neve e gelo. O gelo antártico tem revelado a base de dados paleoclimática de maior resolução para os últimos 800 mil anos. Os padrões de transporte atmosférico refletem a composição e a fonte do particulado encontrado na neve e no gelo do continente Antártico. Estando relacionado a processos climáticos, as características desse transporte alteram em quantidade e qualidade as espécies químicas que se depositam sobre o manto de gelo. Dessa forma, o estudo dos depósitos de particulado ao longo das camadas de neve/gelo na Antártica pode sugerir mudanças nos padrões de transporte atmosférico. Atualmente a comunidade científica discute as diferenças de padrões climáticos entre o leste e o oeste antártico. Enquanto de forma geral observa-se instabilidade no setor oeste, o clima da antártica oriental demonstra relativa estabilidade climática. Neste estudo, analisamos dois testemunhos de gelo recente de duas regiões com características climáticas diferentes do continente Antártico. No Platô Detroit situado na Península Antártica (6410′S/0600′O), analisamos a variabilidade de Black Carbon (BC) ao longo de 20 metros de neve. O BC encontrado na Península Antártica apresentou baixas concentrações comparáveis as encontradas no gelo do Artico período pré-industrial. Nossos resultados sugerem que sua variabiliade corresponde à sazonalidade dos períodos de queimada nos continentes do Hemisfério Sul. No interior do continente Antártico, analisamos o particulado em geral por um processo de microanálise ao longo de um testemunho de 40 metros extraído em Mont Johns (79o55′S/09423′O). Encontramos uma tendência negativa na deposição de poeira mineral (AlSi) entre 1967 e 2007. Nossos resultados sugerem que esta tendência seja resultado de um crescente isolamento atmosférico da região central do continente antártico pelo aumento da intensidade dos ventos ao redor da Antártica. Este aumento na intensidade dos ventos reflete por sua vez o resfriamento da alta atmosfera no centro antártico causado pela depleção da camada de ozônio na região. Adicionalmente, amostras de diferentes microambientes de Patriot Hills (8018′S/08121′O) foram coletadas de maneira asséptica para análise microbiológica. As amostras foram cultivadas em meio R2 e paralelamente o DNA total extraído foi sequenciado pela técnica de pirosequenciamento. Os resultados preliminares desta analise mostram grande riqueza de espécies dos mais variados grupos. Os resultados deste trabalho caracterizam três diferentes parâmetros relacionados a deposição atmosférica em duas áreas pouco exploradas e de grande interesse científico do continente antártico.
The antarctic ice cap stores paleoclimatological information within layers of snow and ice. Antarctic ice has revealed the higher resolution paleoclimactic database for the last 800 kyr. Atmospheric transport plays a fundamental role on the composition and sources of particulate matter found in the Antarctic ice. It has been related to several climatic processes that changes the quantity and quality of exogenous aerosols reaching Antarctica. Therefore, studies of the particulate matter deposits along the snow/ice layers may suggest changes on atmospheric transport patterns. This work, analyze two recent ice cores from two climatic distinct regions of the Antarctic continent. One retrieved from Detroit Plateau/Antarctic Peninsula (6410′S/0600′W), in which we have analyze Black Carbon (BC) deposition and variability along 20 meters of snow. BC found in the Antarctic Peninsula showed low concentrations (varing between 0,014 and 3,733ppb), comparable to the concentrations found on Arctic ice dated from before the industrial revolution period. Our results suggest that peaks of BC detected correspond, mostly, to biomass burning seasons in the South Hemisphere, not speficically from South America. The second one, of 40 m, was retrieved from Central-West Antarctica, Mont Johns (79o55′S/094 23′W), in which we analyzed the mineral dust abundance thought M.E.V. E.D.X. technique. In this study we found negative trends in mineral dust (inferred from Fe, Ti and AlSi) deposition between 1967 and 2007, in contrast to similar works in Sub-antarctic regions. We demonstrate that this trend is a consequence of the persistent atmospheric isolation that encloses the Central and East Antarctic regions due to the increasing winds around Antarctica within this period. It has been documented that westerlies intensification reflect the upper atmosphere cooling above Central Antarctica caused by the stratospherical ozone layer depletion. As part of the polar site characterization, we additionally have performed sampling for microbiological purpose from distinct microenvironments at Patriot Hills (8018′S/08121′W). Samples were cultivated on R2 media and at the same time total DNA on samples was extracted and sent to a pyrosequencing analysis. Preliminary results show richness and diversity of bacterial species distributed on five phyla.
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23

Servettaz, Aymeric. "Deux mille ans d’évolution de la température sur le plateau Est-Antarctique reconstruits à partir des isotopes stables de l’eau et des gaz inertes de la carotte de glace d’Aurora Basin North." Electronic Thesis or Diss., université Paris-Saclay, 2021. http://www.theses.fr/2021UPASJ005.

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L’Antarctique joue un rôle majeur dans le climat de la Terre, car le gradient de température entre l’équateur et les pôles contrôlent la circulation atmosphérique. L’Antarctique est également utile pour comprendre la variabilité du climat, puisque les informations préservées dans la glace peuvent complémenter les observations récentes. Cependant, l’emplacement des forages de carotte de glace sont irrégulièrement répartis sur le continent, et les reconstructions de température sur le plateau Est-Antarctique sont entravées par la faible résolution temporelle résultant d’une trop faible accumulation de neige à haute altitude. Nous présentons ici de nouvelles reconstructions de température à partir de la carotte de glace d’Aurora Basion North (ABN, 77°S, 111°E, 2700 m d’altitude). D’abord, nous utilisons le Modèle Atmosphérique Régional (MAR) pour caractériser le climat récent à ABN, et montrons que les événements de précipitation sont intermittents, et sont marqués par une température 2°C supérieure à la moyenne. Les événements de fortes précipitations sont enregistrés dans les isotopes de l’eau, avec des valeurs de δ18O avoisinant les valeurs estivales, même en hiver, comme l’attestent des mesures dans la neige et le modèle atmosphérique ECHAM5-wiso, qui est équipé avec les isotopes de l’eau. Les précipitations sont systématiquement associées avec un blocage atmosphérique sur la côte de Wilkes Land, au nord-est d’ABN, et ces blocages sont favorisés par les phases négatives du Southern Annular Mode (SAM), le principal mode de variabilité dans le climat de l’hémisphère Sud. Par conséquent, les phases positives du SAM sont marquées par des température froides à ABN, mais pas nécessairement par un δ18O faible, car les précipitations peuvent être réduites. La température reconstruite à partir de la carotte forée à ABN, qui fait 300 m et couvre 2000 ans, reste relativement stable, à ± 1°C de la température moyenne. Nous détaillons une deuxième reconstruction de température faite sur la même carotte, basée sur l’inversion de la température de trou de forage et des anciens gradients de température dans le névé, estimés avec les isotopes stables des gaz Ar et N2 piégés dans les bulles. Cette seconde reconstruction de température révèle deux périodes environ 3°C plus froides à ABN au cours des 2000 dernières années : de 300 à 550 EC, et de 1000 à 1400 EC. Cette anomalie froide médiévale est synchrone avec une phase positive du SAM, et n’a pas pu être identifiée à partir du δ18O seul. Cette étude souligne l’importance d’utiliser plusieurs indicateurs pour déterminer les variations passées de température, car le δ18O pourrait surreprésenter les événements chauds à forte précipitation
Antarctica is a major component in Earth’s climate system, as the equator to pole temperature gradient controls the characteristics of the general circulation of the atmosphere. Antarctica is also very useful to understand climate variability, as past climate information preserved in the ice may help extend the short observational records. However, the ice core drilling locations are unevenly spread across the glaciated continent, and the temperature reconstructions from the high elevation East Antarctic plateau suffer from poor temporal resolution, because low snow accumulation hampers our interpretation of water isotopes. Here, we present new temperature reconstructions from the Aurora Basin North (ABN, 77°S, 111°E, 2700 masl) ice core. First, we use the regional atmospheric model MAR to characterize the recent climate at ABN, and show that precipitation events are intermittent, and occur under temperature 2°C warmer than average. The large precipitation events are marked in the snow isotopes with δ18O values on par with summer levels, even during the winter, as attested by snow measurements and the isotope-enabled atmospheric model ECHAM5-wiso. Precipitations are consistently associated with a blocking on the Wilkes Land coast, North-East of ABN, and the blockings are more likely to occur during negative phases of the Southern Annular Mode (SAM), the main mode of variability in the southern hemisphere climate. Consequently, SAM positive phases are marked by cold temperatures at ABN, but not necessarily low δ18O, as precipitations may be weakened. The temperature reconstructed from the δ18O in the 300-m-deep, 2000-year ice core drilled at ABN supports stable conditions, with a temperature remaining within a ± 1°C range. We present a second temperature reconstruction from the same core, based on the inversion of borehole temperature and past firn temperature gradients, estimated with the stable isotope composition of Ar and N2 gases trapped in bubbles. This second temperature reconstruction, representative of changes in the snow, suggests that temperature at ABN was about 3°C colder during two periods of the last 2000 years: from 300 to 550 CE, and from 1000 to 1400 CE. This medieval cold anomaly is concurrent with a positive SAM phase, and could not be identified from the δ18O alone. This work highlights the importance of using multiple proxies to determine past temperature variability in Antarctica, as δ18O may be biased towards warm precipitation events
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24

Cauquoin, Alexandre. "Flux de 10Be en Antarctique durant les 800 000 dernières années et interprétation." Phd thesis, Université Paris Sud - Paris XI, 2013. http://tel.archives-ouvertes.fr/tel-00954293.

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Les glaces polaires, en plus d'améliorer notre compréhension du climat, donnent accès aux retombées de béryllium-10 (10Be), isotope d'origine cosmogénique formé par l'interaction du rayonnement cosmique et des hautes couches de l'atmosphère. Son taux de production dépend de l'intensité du rayonnement cosmique primaire, qui est modulé par l'activité solaire et le champ magnétique terrestre. Le 10Be contient donc des informations sur ces deux paramètres. Il a permis, entre autres, l'amélioration des chronologies des carottes de glace grâce à des marqueurs stratigraphiques absolus liés à des évènements remarquables du champ géomagnétique comme l'excursion de Laschamp ou l'inversion de Brunhes-Matuyama.EPICA Dome C (75° 06' S, 123° 21' E) est une carotte de glace de 3270 m de long forée en Antarctique Est. Elle offre un enregistrement climatique complet durant les 800 000 dernières années (kyr BP). Dans le cadre de cette thèse, 2200 échantillons de 10Be ont été mesurés entre 2384 m (269 kyr BP) et 2627 m (355 kyr BP) de profondeur. Cette séquence continue offre, d'une part, la possibilité d'étudier l'activité solaire durant la période interglaciaire du Stade Isotopique Marin (MIS) 9.3, où la résolution atteint ~20 ans. Nos résultats contrastent avec ceux durant l'Holocène, avec l'absence remarquée du cycle de de Vries (210 ans) dans notre profil de 10Be. D'autre part, cette séquence nous a permis de vérifier que l'estimation classique de l'accumulation de neige obtenue par les modèles de datation de carottes de glace est correcte à 20% près lors de la succession des cycles glaciaires - interglaciaires.Ces mesures ont été combinées avec celles précédemment effectuées sous la responsabilité de Grant Raisbeck (publication en préparation). Ceci permet de disposer d'un profil continu et détaillé (résolution de 20 à 250 ans) entre 200 et 800 kyr BP sur la carotte de glace EPICA Dome C. Les variations de flux de 10Be observées se comparent bien aux changements d'intensité du champ géomagnétique enregistrés dans les sédiments marins. À partir de cette observation, il est possible de proposer une synchronisation de ces profils afin de les placer sur une échelle d'âge commune. Les déphasages observés entre l'augmentation de température en Antarctique (augmentation du D à EDC) et la hausse du niveau marin global (baisse du 18O marin des archives sédimentaires) n'excèdent pas 3200 ans excepté à la Terminaison VII. La faible résolution des enregistrements de 18O dans les sédiments marins rend l'analyse des déphasages délicate. Les résultats obtenus encouragent à analyser des périodes plus récentes autour de la Terminaison II, incluant les excursions géomagnétiques de Blake et d'Iceland Basin. Ceci permettrait en effet de contraindre plus fortement la synchronisation entre le signal paléomagnétique dans les sédiments marins et le flux de 10Be à EDC.
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25

Krinner, Gerhard. "Simulations du climat des calottes de glace." Phd thesis, Université Joseph Fourier (Grenoble), 1997. http://tel.archives-ouvertes.fr/tel-00716408.

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Ce travail traite de la simulation numérique du climat des grandes calottes de glace, en particulier des calottes de l'Antarctique et du Groenland, toujours existantes, dans des conditions climatiques différentes, à l'aide de modèles de circulation générale de l'atmosphère (MCGA). Le MCGA à grille variable LMDz a été adapté aux spécificités du climat polaire et validé pour le climat actuel. L'approche d'une grille variable, qui permet d'utiliser le MCGA à haute résolution spatiale (autour de 100 km) sur la région d'intérêt à un coût numérique raisonnable, a été validée en analysant la dynamique atmosphérique au bord de la région ciblée à l'aide d'un schéma de suivi des cyclones individuels. Des simulations du climat du Dernier Maximum Glaciaire (DMG) ont été faites pour le Groenland et l'Antarctique et analysées en tenant compte des archives glaciaires disponibles. Une explication possible des différences entre les deux méthodes principales de reconstruction des paléotempératures - l'analyse des isotopes de l'eau et la mesure directe de la température de la glace dans le trou de forage - au centre du Groenland a pu être proposée. Cette explication est basée sur des changements de paramètres climatiques locaux. C'est la première fois que l'approche de grille variable a été utilisée dans un MCGA pour des simulations du climat polaire à l'échelle de quelques années. Les simulations paléoclimatiques faites avec LMDz sont à une résolution spatiale inégalée à ce jour. Finalement, le climat du DMG, simulé par plusieurs MCGA dans le cadre du projet international PMIP (Paleoclimate Modelling Intercomparison Programme), a été analysé, et des implications des résultats pour l'interprétation des enregistrements glaciaires ont été discutées.
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26

Erbland, Joseph. "Contraintes isotopiques sur l'interprétation de l'enregistrement en nitrate dans la carotte de glace de Vostok." Phd thesis, Université de Grenoble, 2011. http://tel.archives-ouvertes.fr/tel-00638761.

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L'ion nitrate (NO3-) présent dans les neiges Antarctiques est issus de l'oxydation des oxydes d'azote (NOx = NO + NO2) dans l'atmosphère. Aux sites de faible accumulation de neige tels que Vostok et Dôme C sur le plateau de l'Est de l'Antarctique, le nitrate n'est pas piégé de manière ultime dans la neige, ce qui limite fortement l'interprétation des enregistrements en nitrate dans les carottes de glace. Des mesures récentes de la composition isotopique en azote du nitrate (δ15N) montrent des valeurs extrêmement élevées (+339‰) dans les premiers décimètres de la neige de Dôme C. Ces valeurs ont été attribuées à la photolyse du nitrate et au recyclage important qui en résulte. Le nitrate possède, par ailleurs, une anomalie isotopique en oxygène (Δ17O) qui permet de tracer l'activité de l'ozone (O3) au cours de sa formation. Ce travail de thèse présente le premier enregistrement de la composition isotopique complète du nitrate (δ15N, Δ17O et δ18O) dans une carotte de glace : la carotte de glace de Vostok dont les 64 échantillons analysés couvrent une période de 150 000 ans. Ce jeu de données a été complété par 313 échantillons collectés entre 2007 et 2010 dans le continuum atmosphère/givre/neige au Dôme C ainsi que dans 21 puits de neige prélevés dans une zone couvrant l'essentiel de l'Est de l'Antarctique. L'analyse isotopique de ces échantillons modernes a permis de contraindre le modèle conceptuel TRANSITS développé au cours de cette thèse et dont le but est de représenter le recyclage du nitrate à l'interface entre l'atmosphère et la neige ainsi que son impact sur la composition isotopique du nitrate archivé. Les valeurs positives et élevées du δ15N du nitrate piégé dans la carotte de glace de Vostok montrent que le recyclage du nitrate a toujours eu lieu sur le plateau Antarctique au cours de la période étudiée. Les variations du flux primaire de nitrate reçu au site de Vostok estimées à l'aide du modèle TRANSITS montrent, en périodes glaciaires, un flux primaire plus important qui pourrait être lié à une dénitrification stratosphérique plus conséquente. Les valeurs de Δ17O du nitrate montrent que l'incursion d'ozone d'origine stratosphérique dans la troposphère était plus fréquente en périodes glaciaires. Nous proposons enfin que les résultats acquis dans le cadre de cette thèse pourraient permettre de mieux contraindre le cycle de l'azote sur la côte Antarctique et d'apporter des éléments d'interprétation des enregistrements en nitrate dans les carottes de glace de sites de plus forte accumulation de neige (au Groenland par exemple).
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27

Delmotte, Marc. "Enregistrements climatiques à Law Dome : variabilité pour les périodes récentes et pour la déglaciation." Phd thesis, Grenoble 1, 1997. http://tel.archives-ouvertes.fr/tel-00759854.

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La complexité du système climatique nécessite de recourir à une grande variété d'indicateurs pour reconstruire ses variations passées. A ce titre, les glaces polaires constituent un outil d'investigation privilégié compte tenu de la grande diversité d'informations qu'elles recèlent. Dans cette étude, nous nous intéressons plus particulièrement au forage antarctique côtier de DSS, sur le site du Law-Dome et aux indicateurs climatiques que constituent les teneurs isotopiques et la teneur en air de la glace. Le nombre d'analyses et la précision des mesures isotopiques requises pour l'étude d'un forage polaire demandent une adaptation et une mise en oeuvre spécifique des techniques classiques de spectrométrie de masse. Notre étude présente une technique nouvelle et originale d'injection des échantillons mise au point sur l'un des spectromètre de masse du laboratoire; elle a permis d'accroître sensiblement le rendement de l'appareil en conservant la précision expérimentale. Récemment de nouvelles études ont remis en cause l'interprétation quantitative classique des isotopes en termes de température. L'analyse de nouveaux échantillons de neige de surface sur la zone de l'Antarctique de l'Est nous permet de discuter la validité de la relation spatiale isotope/température et de proposer une estimation de l'erreur associée. L'utilisation de l'excès en deutérium et d'un modèle isotopique simple apportent une information supplémentaire sur l'origine des précipitations actuelles. Face aux interrogations sur l'impact des activités humaines sur le climat, il est essentiel de replacer les fluctuations récentes dans la cadre de la variabilité climatique naturelle. L'unique résolution temporelle offerte par le forage de DSS nous permet d'étudier en détail le climat des 4000 dernières années. L'analyse spectrale des enregistrements suggère l'existence de modes oscillatoires à rapprocher des phénomènes ENSO et/ou de l'onde circumpolaire antarctique. L'analyse de la teneur en air des échantillons de DSS nous apporte enfin une information sur les variations d'altitude probablement subies par le LawDome au cours de la dernière transition climatique.
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28

Basile, Isabelle. "Origine des aérosols volcaniques et continentaux de la carotte de glace de Vostok (Antarctique)." Phd thesis, Grenoble 1, 1997. http://tel.archives-ouvertes.fr/tel-00756041.

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Déposés en Antarctique de l'Est au cours des 4 derniers cycles climatiques, les aérosols volcaniques (5-50 )um) et continentaux (2-3 )um) de la carotte de Vostok constituent des traceurs de circulations atmosphériques passées. Pour reconstruire leurs trajectoires troposphériques, il est nécessaire d'identifier les sources (volcans ou régions désertiques) à l'origine des émissions des cendres et des poussières continentales. Pour cela, on compare les caractéristiques géochimiques des aérosols avec les caractéristiques des sources potentielles répertoriées. Ces analyses reposent sur les concentrations en éléments majeurs (obtenues par microsonde électronique), en éléments traces (ICPMS), et sur les compositions isotopiques en Strontium et Néodyme (TIMS). Nous avons dû adapter ces méthodes analytiques à la petite taille des aérosols et à leur très faible quantité. Les caractéristiques géochimiques des volcans sources potentiels (latitude>30oS, activité<-500 ka) sont basées sur une synthèse bibliographique. On montre que les cendres des horizons volcaniques analysés proviennent essentiellement de l'arc volcanique des îles Sandwichs (situé dans l'Atlantique Sud, à 5000 km), mais aussi d'Antarctique de l'Ouest et d'Amérique du Sud. De plus, certains horizons peuvent être utilisés comme marqueurs stratigraphiques pour dater (e.g. 141 ka) et corréler les carottes. Les caractéristiques isotopiques (Sr et Nd) des régions désertiques d'Afrique du Sud, d'Australie, du Sud de l'Amérique du Sud, d'Antarctique et de Nouvelle Zélande sont mesurées sur des échantillons prélevés in situ. On remarque qu'il est nécessaire d'utiliser, pour la comparaison avec les aérosols, la fraction granulométrique inférieure à 5 um. Il est ainsi montré que les poussières continentales déposées à Vostok au cours des 4 derniers cycles climatiques proviennent de la Patagonie en période interglaciaire (flux -1,5 mg/m2/an) comme en période glaciaire (flux -20 mg/m2/an). Une partie de cette augmentation de flux peut être expliquée par la présence de vastes épandages de particules détritiques fluvio-glaciaires qui recouvrent, en période glaciaire, la Patagonie et le plateau continental argentin émergé. L'ensemble des sources des aérosols volcaniques et continentaux est donc localisé, quelle que soit la période climatique, dans une région située du côté Atlantique de l'Antarctique, aux moyennes et hautes latitudes. Le transport des particules semble quant à lui être assuré par un courant d'ouest circumpolaire convergent versl'Antarctique. Ce travail montre donc que, à partir des aérosols volcaniques et continentaux, on peut obtenir des paléo-informations dynamiques qui, au travers des corrélations, des datations, ou des modèles de circulation atmosphérique globaux, seront utiles aux reconstitutions des climats du passé.
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29

Armand, Leanne. "The use of diatom transfer functions in estimating sea-surface temperature and sea-ice in cores from the southeast Indian Ocean." Phd thesis, 1997. http://hdl.handle.net/1885/143822.

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30

Mitchell, Logan E. "The late holocene atmospheric methane budget reconstructed from ice cores." Thesis, 2013. http://hdl.handle.net/1957/37906.

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Ice cores are considered the gold standard for recording past climate and biogeochemical changes. However, gas records derived from ice core analysis have until now been largely limited to centennial and longer timescales because sufficient temporal resolution and analytical precision have been lacking, except during rare times when atmospheric concentrations changed rapidly. In this thesis I used a newly developed methane measurement line to make high-resolution, high-precision measurements of methane during the late Holocene (2800 years BP to present). This new measurement line is capable of an analytical precision of < 3 ppb using ~120 g samples whereas the previous highest resolution measurements attained a precision of ± 4.1 ppb using 500-1500g samples [MacFarling Meure et al., 2006]. The reduced sample size requirements as well as automation of a significant portion of the analysis process have enabled me to make >1500 discrete ice core methane measurements and construct the highest resolution records of methane available over the late Holocene. Ice core samples came from the recently completed West Antarctic Ice Sheet (WAIS) Divide ice core which has as one of its primary scientific objectives to produce the highest resolution records of greenhouse gases, and from the Greenland Ice Sheet Project (GISP2) ice core which is a proven paleoclimate archive. My thesis has the following three components. I first used a shallow ice core from WAIS Divide (WDC05A) to produce a 1000 year long methane record with a ~9 year temporal resolution. This record confirmed the existence of multidecadal scale variations that were first observed in the Law Dome, Antarctica ice core. I then explored a range of paleoclimate archives for possible mechanistic connections with methane concentrations on multidecadal timescales. In addition, I present a detailed description of the analytical methods used to obtain high-precision measurements of methane including the effects of solubility and a new chronology for the WDC05A ice core. I found that, in general, the correlations with paleoclimate proxies for temperature and precipitation were low over a range of geographic regions. Of these, the highest correlations were found from 1400-1600 C.E. during the onset of the Little Ice Age and with a drought index in the headwater region of the major East Asian rivers. Large population losses in Asia and the Americas are also coincident with methane concentration decreases indicating that anthropogenic activities may have been impacting multidecadal scale methane variability. In the second component I extended the WAIS Divide record back to 2800 years B.P. and also measured methane from GISP2D over this time interval. These records allowed me to examine the methane Inter-Polar Difference (IPD) which is created by greater northern hemispheric sources. The IPD provides an important constraint on changes in the latitudinal distribution of sources. We used this constraint and an 8-box global methane chemical transport model to examine the Early Anthropogenic Hypothesis which posits that humans began influencing climate thousands of years ago by increasing greenhouse gas emissions and preventing the onset of the next ice age. I found that most of the increase in methane sources over this time came from tropical regions with a smaller contribution coming from the extratropical northern hemisphere. Based on previous modeling estimates of natural methane source changes, I found that the increase in the southern hemisphere tropical methane emissions was likely natural and that the northern hemispheric increase in methane emissions was likely due to anthropogenic activities. These results also provide new constraints on the total magnitude of pre-industrial anthropogenic methane emissions, which I found to be between the high and low estimates that have been previously published in the literature. For the final component of my thesis I assembled a coalition of scientists to investigate the effects of layering on the process of air enclosure in ice at WAIS Divide. Air bubbles are trapped in ice 60-100m below the surface of an ice sheet as snow compacts into solid ice in a region that is known as the Lock-In Zone (LIZ). The details of this process are not known and in the absence of direct measurements previous researchers have assumed it to be a smooth process. This project utilized high-resolution methane and air content measurements as well as density of ice, δ¹⁵N of N₂, and bubble number density measurements to show that air entrapment is affected by high frequency (mm scale) layering in the density of ice within the LIZ. I show that previous parameterizations of the bubble closure process in firn models have not accounted for this variability and present a new parameterization which does. This has implications for interpreting rapid changes in trace gases measured in ice cores since variable bubble closure will impact the smoothing of those records. In particular it is essential to understand the details of this process as new high resolution ice core records from Antarctica and Greenland examine the relative timing between greenhouse gases and rapid climate changes.
Graduation date: 2013
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31

Bader, Nicole Ann. "Provenance of the ice-cored moraine at Mt. Achernar, Law Glacier, Antarctica." Thesis, 2014. http://hdl.handle.net/1805/5674.

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Glacial till from the Mt. Achernar moraine (MAM) records pre- and post- last glacial maximum (LGM) compositional variability of an East Antarctic moraine sequence through time and space. Pebble lithology, detrital zircon geochronology, and till geochemistry were analyzed on samples from a 6.5 km transect. Hummocky topography occurs with the most recently exposed material along the active ice margin (Zone 1), followed by a relatively flat and low region (Zone 2), and then a series of ~2 m high parallel/sub-parallel ridges and troughs accompanied by distinct color changes that are directly related to the dominant lithology of the region (Zones 3–5). Zone 3 is dominated by ~38% more sedimentary rocks than adjacent zones and has an overall shape of a broad arch superimposed with smaller ridges. Zone 4 is composed of distinct colored bands that alternate between dominant sedimentary and mafic igneous lithologies. These dominant sedimentary and intermediate/mafic igneous rocks for all Zones are interpreted to be primarily the Beacon and Ferrar Supergroup rocks respectively. The U/Pb data from the till is consistent with a Beacon Supergroup source as samples consistently show significant populations from the Permian ~250-260 Ma, the Proterozoic ~565–600 Ma, ~950–1270 Ma, and ~2300-2320 Ma, as well as (and) the late Archean ~2700-2770 Ma. The Pagoda, Mackellar, Buckley, and Fremouw Formations are potential sources of the detrital zircons. When paired with surface exposure ages, the U/Pb data indicates that the debris source has been consistent over the past ~555 ka, implying relatively stable ice sheet behavior. However, ice sheet change is indicated by a trim line present on Mt. Achernar that can be traced back to the boundary between Zones 3 and 4, as well as a change in pebble lithology, geochemistry, and morphology of Zone 3. Zone 3 records a time of ice sheet thickening and a change in provenance during the LGM. Zone 4 is pre-LGM, Zone 2 records deglaciation, and Zone 1 is still actively connected to the Law Glacier. This study reveals the broader importance of using multiple provenance techniques when interpreting provenance changes in till over time.
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32

Dennis, Donovan. "Enrichment of surface ice stable water isotope ratios following sublimation." Thesis, 2018. https://hdl.handle.net/2144/33056.

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Stable isotopes of water preserved in glaciers and icesheets have revolutionized our understanding of terrestrial paleoclimate. Post-deposition alteration of the stable water isotope ratios in snow and ice can obscure the original meteoric signal, therefore altering the interpretation of δ18O and δD as records of paleo-temperatures in ice. The effects of sublimation on δ18O and δD are not well-understood for massive (non-snow) ice and have been largely overlooked, particularly within the experimental literature. We present results from a series of environmental chamber experiments investigating alteration of the in-situ signal following sublimation. Our data suggest that sublimation enriches the ice remaining after sublimation in 18O and D. This is observed both in surface ice and in the signal of the ice at depth. These results could have important implications for studies utilizing surface ice δ18O and δD for reconstructions of paleoclimate.
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