@phdthesis{Schlemm2022,
  author    = {Schlemm, Tanja},
  title     = {The marine ice cliff instability of the Antarctic ice sheet},
  doi       = {10.25932/publishup-58633},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-586333},
  school      = {Universit{\"a}t Potsdam},
  pages     = {107},
  year      = {2022},
  abstract  = {The Antarctic ice sheet is the largest freshwater reservoir worldwide. If it were to melt completely, global sea levels would rise by about 58 m. Calculation of projections of the Antarctic contribution to sea level rise under global warming conditions is an ongoing effort which yields large ranges in predictions. Among the reasons for this are uncertainties related to the physics of ice sheet modeling. These uncertainties include two processes that could lead to runaway ice retreat: the Marine Ice Sheet Instability (MISI), which causes rapid grounding line retreat on retrograde bedrock, and the Marine Ice Cliff Instability (MICI), in which tall ice cliffs become unstable and calve off, exposing even taller ice cliffs. In my thesis, I investigated both marine instabilities (MISI and MICI) using the Parallel Ice Sheet Model (PISM), with a focus on MICI.},
  language  = {en}
}
@phdthesis{Hultzsch2006,
  author    = {Hultzsch, Nadja},
  title     = {Lakustrine Sedimente als Archive des sp{\"a}tquart{\"a}ren Umweltwandels in der Amery-Oase, Ostantarktis},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-7980},
  school      = {Universit{\"a}t Potsdam},
  year      = {2006},
  abstract  = {Im Rahmen einer deutsch-australischen Forschungskooperation erfolgte im S{\"u}dsommer 2001/2002 eine Expedition in die Amery-Oase (70°50'S, 68°00'E), die im Einzugsgebiet des Lambert-Gletscher/Amery-Schelfeis-Systems, dem gr{\"o}ßten ostantarktischen Eis-Drainagesystem, liegt. Von deutscher Seite wurden im Zuge der Gel{\"a}ndekampagne erstmals lakustrine Sedimentsequenzen gewonnen, um die bislang wenig erforschte sp{\"a}tquart{\"a}re Klima- und Umweltgeschichte dieser rund 1800 km<sup>2 großen eisfreien Region zu rekonstruieren. Die drei untersuchten Glazialseen Beaver, Radok und Terrasovoje unterscheiden sich sowohl deutlich in ihrer Gr{\"o}ße, Bathymetrie und den hydrologischen Merkmalen sowie in ihren Sedimentabfolgen. Einen Schwerpunkte dieser Doktorarbeit bildet die Rekonstruktion der Sedimentationsprozesse und des Ablagerungsmilieus sowie Untersuchungen zur Herkunft des detritischen Sedimentmaterials in den Seebecken. Der methodische Ansatz verfolgt die Charakterisierung der klastischen Sedimentfazies an Hand lithologisch-granulometrischer Merkmale sowie mineralogisch-geochemischer Analysen der Sedimentherkunft. Ein weiterer Schwerpunkt ist die Rekonstruktion der holoz{\"a}nen biogen gesteuerten Ablagerungsbedingungen im Terrasovoje-See, die R{\"u}ckschl{\"u}sse auf den kurzfristigen postglazialen Klima- und Umweltwandel in der Amery-Oase gestattet. Dabei wurden mikrofazielle Untersuchungsmethoden und hochaufl{\"o}sende Elementscannermessungen angewandt. Die klastische Sedimentherkunft in den drei Seen unterscheidet sich r{\"a}umlich deutlich voneinander und spiegelt den komplexen geologischen Aufbau der Amery-Oase wider. Als Sedimentquellen konnten pr{\"a}kambrische Metamorphite, permotriassische Sedimentgesteine und terti{\"a}re Lockersedimente identifiziert werden. Die Varibilit{\"a}t der Herkunftssignale ist zeitlich weniger deutlich als r{\"a}umlich ausgepr{\"a}gt und deutet auf relativ konstante Liefergebiete in den einzelnen Seen hin. Das glaziolakustrine Ablagerungsmilieu der drei untersuchten Seen zeigt klare r{\"a}umliche und zeitliche Unterschiede. In allen drei Seen setzen sich die {\"a}lteren Sedimente aus grobk{\"o}rnigem, h{\"a}ufig diamiktischem Material zusammen, w{\"a}hrend die j{\"u}ngeren Sedimente aus feink{\"o}rnigen Laminiten bestehen. Die lithofazielle Zweiteilung in den Sedimentabfolgen deutet auf einen R{\"u}ckzug der Gletscher und/oder einen Anstieg der Wassertiefen im {\"U}bergang von den grobk{\"o}rnigen zu den feink{\"o}rnigen Ablagerungseinheiten hin. Die oberen feink{\"o}rnigen Kernabschnitte spiegeln in allen drei Seen die postglaziale lakustrine Sedimentation wider. Im Beaver-See wird die postglaziale Fazies durch laminierte klastische Stillwassersedimente repr{\"a}sentiert, im Radok-See durch Turbiditsequenzen und im Terrasovoje-See durch Algenlaminite. Abgesehen vom Terrasovoje-See ist die zeitliche Einordnung der Fazieswechsel auf Grund mangelnder Altersinformationen schwer erfassbar. Im Terrasovoje-See setzte die postglaziale Sedimentation um rund 12,4 cal. ka ein. Somit weisen die darunterliegenden glazigenen Klastika mindestens ein sp{\"a}tpleistoz{\"a}nes Alter auf. Die sedimentologischen Eigenschaften, {\"A}nderungen der Sedimentationsraten und organogene Zusammensetzung der postglazialen Biogenlaminite des Terrasovoje-Sees deuten auf Variationen der pal{\"a}olimnologischen Bedingungen hinsichtlich Eisbedeckung, biologischer Produktivit{\"a}t, Wasserstand, Redoxbedingungen und Salinit{\"a}t hin, die mit regionalen holoz{\"a}nen Klima{\"a}nderungen in Verbindung gebracht werden k{\"o}nnen. Weitere Anhaltspunkte ergeben sich aus der Zusammensetzung und den M{\"a}chtigkeitsvariationen der Laminae, die generell aus Wechsellagerungen von Cyanobakterienmatten mit feinklastischen Lagen bestehen. Lagenz{\"a}hlungen der Laminae belegen {\"A}nderungen des Ablagerungsmilieus auf subdekadischen Zeitskalen, wobei zeitweilige j{\"a}hrliche Signale nicht ausgeschlossen werden k{\"o}nnen. Unter Ber{\"u}cksichtigung aller faziellen Indikatoren l{\"a}sst sich aus der Sedimentabfolge des Terrasovoje-Sees ein fr{\"u}hholoz{\"a}nes Klimaoptimum zwischen 9 und 7 cal. ka sowie weitere W{\"a}rmephasen zwischen 3,2 und 2,3 cal. ka sowie 1,5 und 1,0 cal. ka ableiten. Im Vergleich mit Eiskernarchiven und anderen Seesedimentabfolgen aus ostantarktischen Oasen zeigt sich, dass das Auftreten postglazialer Warmphasen nicht allenorts einem allgemein g{\"u}ltigen r{\"a}umlich-zeitlichen Muster folgt. Die Ursachen hierf{\"u}r liegen vermutlich in den lokalen geographischen Gegebenheiten. Es l{\"a}sst sich daraus schliessen, dass die bisher vorliegenden Klimarekonstruktionen eher das Lokalklima an einem Untersuchungsstandort als das Großklima der Ostantarktis reflektieren. Daraus ergibt sich die Notwendigkeit weiterer Untersuchungen von antarktischen Klimaarchiven und Untersuchungsstandorten, um {\"o}rtliche von {\"u}berregionalen Klimasignalen besser unterscheiden zu k{\"o}nnen.},
  subject      = {Antarktis},
  language  = {de}
}
@phdthesis{Muench2018,
  author    = {M{\"u}nch, Thomas},
  title     = {Interpretation of temperature signals from ice cores},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-414963},
  school      = {Universit{\"a}t Potsdam},
  pages     = {xxi, 197},
  year      = {2018},
  abstract  = {Earth's climate varies continuously across space and time, but humankind has witnessed only a small snapshot of its entire history, and instrumentally documented it for a mere 200 years. Our knowledge of past climate changes is therefore almost exclusively based on indirect proxy data, i.e. on indicators which are sensitive to changes in climatic variables and stored in environmental archives. Extracting the data from these archives allows retrieval of the information from earlier times. Obtaining accurate proxy information is a key means to test model predictions of the past climate, and only after such validation can the models be used to reliably forecast future changes in our warming world. The polar ice sheets of Greenland and Antarctica are one major climate archive, which record information about local air temperatures by means of the isotopic composition of the water molecules embedded in the ice. However, this temperature proxy is, as any indirect climate data, not a perfect recorder of past climatic variations. Apart from local air temperatures, a multitude of other processes affect the mean and variability of the isotopic data, which hinders their direct interpretation in terms of climate variations. This applies especially to regions with little annual accumulation of snow, such as the Antarctic Plateau. While these areas in principle allow for the extraction of isotope records reaching far back in time, a strong corruption of the temperature signal originally encoded in the isotopic data of the snow is expected. This dissertation uses observational isotope data from Antarctica, focussing especially on the East Antarctic low-accumulation area around the Kohnen Station ice-core drilling site, together with statistical and physical methods, to improve our understanding of the spatial and temporal isotope variability across different scales, and thus to enhance the applicability of the proxy for estimating past temperature variability. The presented results lead to a quantitative explanation of the local-scale (1-500 m) spatial variability in the form of a statistical noise model, and reveal the main source of the temporal variability to be the mixture of a climatic seasonal cycle in temperature and the effect of diffusional smoothing acting on temporally uncorrelated noise. These findings put significant limits on the representativity of single isotope records in terms of local air temperature, and impact the interpretation of apparent cyclicalities in the records. Furthermore, to extend the analyses to larger scales, the timescale-dependency of observed Holocene isotope variability is studied. This offers a deeper understanding of the nature of the variations, and is crucial for unravelling the embedded true temperature variability over a wide range of timescales.},
  language  = {en}
}
@phdthesis{Bajerski2013,
  author    = {Bajerski, Felizitas},
  title     = {Bacterial communities in glacier forefields of the Larsemann Hills, East Antarctica : structure, development \& adaptation},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-67424},
  school      = {Universit{\"a}t Potsdam},
  year      = {2013},
  abstract  = {Antarctic glacier forfields are extreme environments and pioneer sites for ecological succession. The Antarctic continent shows microbial community development as a natural laboratory because of its special environment, geographic isolation and little anthropogenic influence. Increasing temperatures due to global warming lead to enhanced deglaciation processes in cold-affected habitats and new terrain is becoming exposed to soil formation and accessible for microbial colonisation. This study aims to understand the structure and development of glacier forefield bacterial communities, especially how soil parameters impact the microorganisms and how those are adapted to the extreme conditions of the habitat. To this effect, a combination of cultivation experiments, molecular, geophysical and geochemical analysis was applied to examine two glacier forfields of the Larsemann Hills, East Antarctica. Culture-independent molecular tools such as terminal restriction length polymorphism (T-RFLP), clone libraries and quantitative real-time PCR (qPCR) were used to determine bacterial diversity and distribution. Cultivation of yet unknown species was carried out to get insights in the physiology and adaptation of the microorganisms. Adaptation strategies of the microorganisms were studied by determining changes of the cell membrane phospholipid fatty acid (PLFA) inventory of an isolated bacterium in response to temperature and pH fluctuations and by measuring enzyme activity at low temperature in environmental soil samples. The two studied glacier forefields are extreme habitats characterised by low temperatures, low water availability and small oligotrophic nutrient pools and represent sites of different bacterial succession in relation to soil parameters. The investigated sites showed microbial succession at an early step of soil formation near the ice tongue in comparison to closely located but rather older and more developed soil from the forefield. At the early step the succession is influenced by a deglaciation-dependent areal shift of soil parameters followed by a variable and prevalently depth-related distribution of the soil parameters that is driven by the extreme Antarctic conditions. The dominant taxa in the glacier forefields are Actinobacteria, Acidobacteria, Proteobacteria, Bacteroidetes, Cyanobacteria and Chloroflexi. The connection of soil characteristics with bacterial community structure showed that soil parameter and soil formation along the glacier forefield influence the distribution of certain phyla. In the early step of succession the relative undifferentiated bacterial diversity reflects the undifferentiated soil development and has a high potential to shift according to past and present environmental conditions. With progressing development environmental constraints such as water or carbon limitation have a greater influence. Adapting the culturing conditions to the cold and oligotrophic environment, the number of culturable heterotrophic bacteria reached up to 108 colony forming units per gram soil and 148 isolates were obtained. Two new psychrotolerant bacteria, Herbaspirillum psychrotolerans PB1T and Chryseobacterium frigidisoli PB4T, were characterised in detail and described as novel species in the family of Oxalobacteraceae and Flavobacteriaceae, respectively. The isolates are able to grow at low temperatures tolerating temperature fluctuations and they are not specialised to a certain substrate, therefore they are well-adapted to the cold and oligotrophic environment. The adaptation strategies of the microorganisms were analysed in environmental samples and cultures focussing on extracellular enzyme activity at low temperature and PLFA analyses. Extracellular phosphatases (pH 11 and pH 6.5), β-glucosidase, invertase and urease activity were detected in the glacier forefield soils at low temperature (14°C) catalysing the conversion of various compounds providing necessary substrates and may further play a role in the soil formation and total carbon turnover of the habitat. The PLFA analysis of the newly isolated species C. frigidisoli showed that the cold-adapted strain develops different strategies to maintain the cell membrane function under changing environmental conditions by altering the PLFA inventory at different temperatures and pH values. A newly discovered fatty acid, which was not found in any other microorganism so far, significantly increased at decreasing temperature and low pH and thus plays an important role in the adaption of C. frigidisoli. This work gives insights into the diversity, distribution and adaptation mechanisms of microbial communities in oligotrophic cold-affected soils and shows that Antarctic glacier forefields are suitable model systems to study bacterial colonisation in connection to soil formation.},
  language  = {en}
}
@phdthesis{Glushak2007,
  author    = {Glushak, Ksenia},
  title     = {Atmospheric circulation and the surface mass balance in a regional climate model of Antarctica},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-17296},
  school      = {Universit{\"a}t Potsdam},
  year      = {2007},
  abstract  = {Understanding the Earth's climate system and particularly climate variability presents one of the most difficult and urgent challenges in science. The Antarctic plays a crucial role in the global climate system, since it is the principal region of radiative energy deficit and atmospheric cooling. An assessment of regional climate model HIRHAM is presented. The simulations are generated with the HIRHAM model, which is modified for Antarctic applications. With a horizontal resolution of 55km, the model has been run for the period 1958-1998 creating long-term simulations from initial and boundary conditions provided by the European Centre for Medium-Range Weather Forecasts (ECMWF) ERA40 re-analysis. The model output is compared with observations from observation stations, upper air data, global atmospheric analyses and satellite data. In comparison with the observations, the evaluation shows that the simulations with the HIRHAM model capture both the large and regional scale circulation features with generally small bias in the modeled variables. On the annual time scale the largest errors in the model simulations are the overestimation total cloud cover and the colder near-surface temperature over the interior of the Antarctic plateau. The low-level temperature inversion as well as low-level wind jet is well captured by the model. The decadal scale processes were studied based on trend calculations. The long-term run was divided into two 20 years parts. The 2m temperature, 500 hPa temperature, MSLP, precipitation and net mass balance trends were calculated for both periods and over 1958 - 1998. During the last two decades the strong surface cooling was observed over the Eastern Antarctica, this result is in good agreement with the result of Chapman and Walsh (2005) who calculated the temperature trend based on the observational data. The MSLP trend reveals a big disparity between the first and second parts of the 40 year run. The overall trend shows the strengthening of the circumpolar vortex and continental anticyclone. The net mass balance as well as precipitation show a positive trend over the Antarctic Peninsula region, along Wilkes Land and in Dronning Maud Land. The Antarctic ice sheet grows over the Eastern part of Antarctica with small exceptions in Dronning Maud Land and Wilkes Land and sinks in the Antarctic Peninsula; this result is in good agreement with the satellite-measured altitude presented in Davis (2005) . To better understand the horizontal structure of MSLP, temperature and net mass balance trends the influence of the Southern Annual Mode (SAM) on the Antarctic climate was investigated. The main meteorological parameters during the positive and negative Antarctic Oscillation (AAO) phases were compared to each other. A positive/negative AAO index means strengthening/weakening of the circumpolar vortex, poleward/northward storm tracks and prevailing/weakening westerly winds. For detailed investigation of global teleconnection, two positive and one negative periods of AAO phase were chosen. The differences in MSLP and 2m temperature between positive and negative AAO years during the winter months partly explain the surface cooling during the last decades.},
  language  = {en}
}