Glacier mass balance measurements on Fourcade and Polar Club glacier, King George Island

The east coast of the AP is highly influenced by cold and dry air masses stemming from the adjacent Weddell Sea. By the contrary, the west coast jointly with the South Shetland Islands are directly exposed to the humid and relatively warm air masses from the South Pacific Ocean carried by the strong and persistent westerly winds. Systematic glaciological field studies are very scarce on both sides of the AP, among them can be mentioned a mass-balance program performed continuously since summer 1998/99 by the Instituto Antártico Argentino (IAA) on Vega Island, James Ross Archipelago, on the northeastern flank of the AP. Another continuous plurianual glaciological research has been initiated in 2010 jointly by the University of Bonn and the IAA at the Fourcade Glacier on King George Island (KGI) within the framework of the ESF project IMCOAST (FK 03F0617B). Two transects of mass balance stakes were installed from the top of the Warszawa Ice Dome down to the border of the glaciers Fourcade and Polar Club, to serve for calibration and validation of modeling efforts. The stakes were measured at the beginning and end of each summer field campaign in November 2010, February - March 2011, January - March 2012, and especially during the austral winter 2012 up to March 2013 every 10 to 14 days depending on weather conditions. During the austral winter 2013 and until June 2014 the measurements were conducted every 20 to 30 days, weather permitting. Snow density was measured as well in every field trip from June 2012 until June 2104, establishing a rather homogeneous value along the different parts of the glacier. Snow density in late summer, rho_s is usually higher than the one in late winter, rho_w. Seasonal average values were calculated for the area covered by the mass balance stakes, being rho_s= 471 Kg/m**3 and rho_w = 363 Kg/m**3.

31 ground-penetrating radar lines of Area 3 - Beach ridge plain (high wave energy) from Maxwell Bay, King George Island, Antarctic Peninsula

During a field campaign in the Austral spring 2012 the sedimentary architecture of a polar gravel-beach system at the southern coast of Potter Peninsula (Area 3) was revealed using ground-penetrating radar (GPR, Geophysical Survey Systems, Inc. SIR-3000). 31 profiles were collected using a mono-static 200 MHz antenna operated in common offset mode. Trace increment was set to 0.05 m. A differential global-positioning system (dGPS, Leica GS09) was used to obtain topographical information along the GPR lines. GPR data are provided in RADAN-Format, dGPS coordinates are provided in ascii format; projection is UTM (WGS 84, zone 21S).

Satellite image map of King George Island, Antarctica

A new topographic database for King George Island, one of the most visited areas in Antarctica, is presented. Data from differential GPS surveys, gained during the summers 1997/98 and 1999/2000, were combined with up to date coastlines from a SPOT satellite image mosaic, and topographic information from maps as well as from the Antarctic Digital Database. A digital terrain model (DTM) was generated using ARC/INFO GIS. From contour lines derived from the DTM and the satellite image mosaic a satellite image map was assembled. Extensive information on data accuracy, the database as well as on the criteria applied to select place names is given in the multilingual map. A lack of accurate topographic information in the eastern part of the island was identified. It was concluded that additional topographic surveying or radar interferometry should be conducted to improve the data quality in this area. In three case studies, the potential applications of the improved topographic database are demonstrated. The first two examples comprise the verification of glacier velocities and the study of glacier retreat from the various input data-sets as well as the use of the DTM for climatological modelling. The last case study focuses on the use of the new digital database as a basic GIS (Geographic Information System) layer for environmental monitoring and management on King George Island.

Recent ostracods in surface sediment samples from Admiralty Bay, King George Island, West Antarctica

Ostracods from Admiralty Bay on King George Island (South Shetland Islands) represent 29 podocopid species, belonging to 19 genera, one cladocopid and six myodocopid species. They were recovered from Recent marine and/or glacio-marine sediment samples from water depths of up to 520 m. These ostracods constitute a variable assemblage, which is overall typical for the Antarctic environment. Shallow-water assemblages tend to be more variable in terms of frequencies and species richness than deep-water assemblages. The later are low in numbers and remain relatively high diversities. Overall, no linear relation between ostracod assemblage-composition and environmental features analyzed was recognized.

Equivalent dose, dose rate and age determination of cobble surfaces in the Antarctic

Most current methods of reconstructing past sea levels within Antarctica rely on radiocarbon dating. However, radiocarbon dating is limited by the availability of material for dating and problems inherent with radiocarbon reservoirs in Antarctic marine systems. Here we report on the success of a new approach to dating raised beach deposits in Antarctica for the purpose of reconstructing past sea levels. This new approach is the use of optically stimulated luminescence (OSL) on quartz-grains obtained from the underside of cobbles within raised beaches and boulder pavements. We obtained eight OSL dates from three sites along the shores of Maxwell Bay in the South Shetland Islands of the Antarctic Peninsula. These dates are internally consistent and fit well with previously published radiocarbon ages obtained from the same deposits. In addition, when the technique was applied to a modern beach, it resulted in an age of zero. Our results suggest that this method will provide a valuable tool in the reconstruction of past sea levels in Antarctica and other coarse-grained beach deposits across the globe.

Timing of the most recent Neoglacial advance and retreat in Potter Cove, Antarctic Peninsula

The timing of the most recent Neoglacial advance in the Antarctic Peninsula is important for establishing global climate teleconnections and providing important post-glacial rebound corrections to gravity-based satellite measurements of ice loss. However, obtaining accurate ages from terrestrial geomorphic and sedimentary indicators of the most recent Neoglacial advance in Antarctica has been hampered by the lack of historical records and the difficulty of dating materials in Antarctica. Here we use a new approach to dating flights of raised beaches in the South Shetland Islands of the northern Antarctic Peninsula to bracket the age of a Neoglacial advance that occurred between 1500 and 1700 AD, broadly synchronous with compilations for the timing of the Little Ice Age in the northern hemisphere. Our approach is based on optically stimulated luminescence of the underside of buried cobbles to obtain the age of beaches previously shown to have been deposited immediately inside and outside the moraines of the most recent Neoglacial advance. In addition, these beaches mark the timing of an apparent change in the rate of isostatic rebound thought to be in response to the same glacial advance within the South Shetland Islands. We use a Maxwell viscoelastic model of glacial-isostatic adjustment (GIA) to determine whether the rates of uplift calculated from the raised beaches are realistic given the limited constraints on the ice advance during this most recent Neoglacial advance. Our rebound model suggests that the subsequent melting of an additional 16-22% increase in the volume of ice within the South Shetland Islands would result in a subsequent uplift rate of 12.5 mm/yr that lasted until 1840 AD resulting in a cumulative uplift of 2.5 m. This uplift rate and magnitude are in close agreement with observed rates and magnitudes calculated from the raised beaches since the most recent Neoglacial advance along the South Shetland Islands and falls within the range of uplift rates from similar settings such as Alaska.

Sedimentology on two core from the Bransfield Strait area

The raw material for these investigations are samples from marine (sub)surface sediments around the northern part of the Antarctic Peninsula. They had been sampled in the years 1981 to 1986 during several expeditions of the research vessels Meteor, Polarstern and Walther Herwig. 83 box core, gravity core and dredge samples from the area of the Bransfield Strait, the Powell Basin and the northern Weddell Sea have been examined for their grain-size distribution, their mineralogical and petrographical composition. Silt prevails and its clay proportions exceed 25% wt. in water depths greater than 2000 m. The granulometrical results reveal some typical sedimentation processes within the area of investigation. While turbiditic processes together with sediment input from melting icebergs control the sedimentation in the Weddell Sea, the South Orkney Island Plateau and the Powell Basin, the fine grained material from Bransfield Strait mainly relies on marine currents in the shelf area. In addition, the direct sediment input of coarse shelf sediments from the Bransfield Strait into the Powell Basin through submarine canyons could be proven. Variations in the grain-size composition with sediment depth are smalI. The mineral composition of the clay and fine silt fractions is quite uniform in all samples. There are (in decreasing order): illite, montmorillonite, chlorite, smectite, mixed-Iayers, as well as detrital quartz and feldspars. A petrographically based sediment stratigraphy can be established in using the considerable changes in the chlorite- and Ca-plagioclase portions in samples from Core 224. For this sedimentation area a mean sedimentation rate of 7 cm/1000 a is assumed. Remarkable changes in the portions of amorphous silica components - diatom skeletons and volcanic glass shards - appear all over the area of investigation. They contribute between 4-83 % to the clay and fine silt fraction. Several provinces according to the heavy mineral assemblages in the fine sand fraction can be distinguished: (i) a province remarkably influenced by minerals of volcanic origin south and north of the South Shetland Islands; (ii) a small strip with sediment dominated by plutonic material along the western coast of the Antarctic Peninsula and (iii) a sediment controlled by metamorphic minerals and rock fragments in the area of the Weddell Sea and Elephant Island. While taking the whole grain-size spectrum into account a more comprehensive interpretation can be given: the accessoric but distinct appearance of tourmaline, rutile and zircon in the heavy mineral assembly along the northwestern coast of the Antarctic Peninsula is in agreement with the occurrence of acid volcanic rock pieces in the coarse fraction of the ice load detritus in this region. In the vicinity of the South Shetland Islands chlorite appears in remarkable portions in the clay fraction in combination with leucoxene, sphene and olivine, and pumice as well as pyroclastic rocks in the medium and coarse grain fractions, respectively. Amphiboles and amphibole-schists are dominant on the South Orkney Island Plateau. In the sediments of the northwestern Weddell Sea the heavy mineral phases of red spinel, garnet, kyanite and sillimanite in connection with medium to highgrade metamorphic rocks especially granulitic gneisses, are more abundant. A good conformity between the ice rafted rock sampIes and the rocks in the island outcrops could be proven, especially in the vicinity of offshore islands nearby. On the continent enrichments of rock societies and groups appear in spacious outlines: acid effusive rocks in the west of the ice divide on the Antarctic Peninsula, clastic sedimentites at the tip of the Antarctic Peninsula and granoblastic gneisses in central and eastern Antarctica. Coarse grain detritus with more than 1 cm of diameter must have been rafted by icebergs. These rock fragments are classified as rock types, groups and societies. The spacial distribution of their statistically determined weight relations evidently shows the paths of the iceberg drift and in nexus with already known iceberg routes also point to the possible areas of provenance, provided that the density of sample locations and the number of rock pieces are sufficient.

21 ground-penetrating radar lines of Area 1 - Beach ridge plain (low wave energy) from Potter Cove, King George Island, Antarctic Peninsula

During two field campaigns (Austral springs 2011 and 2012) the sedimentary architecture of a polar gravel-beach system at the western coast of Potter Peninsula (Area 1) was revealed using ground-penetrating radar (GPR, Geophysical Survey Systems, Inc. SIR-3000). 21 profiles were collected using a mono-static 200 MHz antenna operated in common offset mode. Trace increment was set to 0.05 m. A differential global-positioning system (dGPS, Leica GS09) was used to obtain topographical information along the GPR lines. GPR data are provided in RADAN-Format, dGPS coordinates are provided in ascii format; projection is UTM (WGS 84, zone 21S).

49 ground-penetrating radar lines of Area 2 - Gravel cuspate spit with gravel beach ridges from Potter Cove, King George Island, Antarctic Peninsula

During two field campaigns (Austral springs 2011 and 2012) the sedimentary architecture of a polar gravel-beach system at the southwestern coast of Potter Peninsula (Area 2) was revealed using ground-penetrating radar (GPR, Geophysical Survey Systems, Inc. SIR-3000). 49 profiles were collected using a mono-static 200 MHz antenna operated in common offset mode. Trace increment was set to 0.05 m. A differential global-positioning system (dGPS, Leica GS09) was used to obtain topographical information along the GPR lines. GPR data are provided in RADAN-Format, dGPS coordinates are provided in ascii format; projection is UTM (WGS 84, zone 21S).

Sensitivity of a distributed temperature-radiation index melt model based on AWS observations and surface energy balance fluxes, Hurd Peninsula glaciers, Livingston Island, Antarctica

We use an automatic weather station and surface mass balance dataset spanning four melt seasons collected on Hurd Peninsula Glaciers, South Shetland Islands, to investigate the point surface energy balance, to determine the absolute and relative contribution of the various energy fluxes acting on the glacier surface and to estimate the sensitivity of melt to ambient temperature changes. Long-wave incoming radiation is the main energy source for melt, while short-wave radiation is the most important flux controlling the variation of both seasonal and daily mean surface energy balance. Short-wave and long-wave radiation fluxes do, in general, balance each other, resulting in a high correspondence between daily mean net radiation flux and available melt energy flux. We calibrate a distributed melt model driven by air temperature and an expression for the incoming short-wave radiation. The model is calibrated with the data from one of the melt seasons and validated with the data of the three remaining seasons. The model results deviate at most 140 mm w.e. from the corresponding observations using the glaciological method. The model is very sensitive to changes in ambient temperature: a 0.5 ◦ C increase results in 56 % higher melt rates.

Caracterización dinámica del glaciar Hurd combinando observaciones de campo y simulaciones numéricas

El objetivo fundamental de esta tesis es la caracterización de la morfología y del estado de deformaciones y tensiones del Glaciar Hurd (Isla Livingston, Archipiélago de las Shetland del Sur, Antártida), mediante una combinación de observaciones de campo, registros de georradar y simulaciones numéricas. La morfología y el estado de deformaciones y tensiones actuales son la expresión de la evolución dinámica del glaciar desde tiempos pretéritos hasta recientes, y su análisis nos dará las pautas con las cuales ser capaces de predecir, con el apoyo de las simulaciones numéricas, su evolución futura. El primer aspecto que se aborda es el estudio de las estructuras que pueden observarse en la superficie del glaciar. Describimos las distintas técnicas utilizadas (medidas de campo, fotointerpretación de ortofotografías, análisis geoquímico de cenizas volcánicas, etc.) y presentamos el análisis e interpretación de los resultados morfo-estructurales, así como la correlación, mediante análisis geoquímicos (fluorescencia de rayos X), entre las cenizas volcánicas que extruyen en la superficie del Glaciar Hurd y las del volcán Decepción, origen de las cenizas. Esto nos permite realizar una datación de las mismas como Tefra 1, correspondiente a la erupción de 1970, Tefra 2, correspondiente a las erupciones pre-1829, y el conjunto Tefra 3, asociado a las erupciones más antiguas. En segundo lugar nos ocupamos de las estructuras presentes en el interior del glaciar, cuya herramienta de detección fundamental es el georradar. Identificadas estas estructuras internas, las vinculamos con las observadas en la superficie del glaciar. También hemos estudiado la estructura hidrotérmica del glaciar, obteniendo una serie de evidencias adicionales de su carácter politérmico. Entre éstas se contaban, hasta ahora, las basadas en el valor del parámetro de rigidez de la relación constitutiva del hielo determinada por ajuste de modelos dinámicos y observaciones realizados por Otero (2008) y las basadas en las velocidades de las ondas de radar en el hielo determinadas con el método de punto medio común por Navarro y otros (2009). Las evidencias adicionales que aportamos en esta tesis son: 1) la presencia de estructuras típicas de régimen compresivo en la zona terminal del glaciar y de cizalla en los márgenes del mismo, y 2) la presencia de un estrato superficial de hielo frío (por encima de otro templado) en la zona de ablación de los tres lóbulos del Glaciar Hurd –Sally Rocks, Argentina y Las Palmas–, que alcanzan espesores de 70, 50 y 40 m, respectivamente. Este estrato de hielo frío está probablemente congelado al lecho subglaciar en la zona terminal (Molina y otros, 2007; esta tesis). Por último, nos ocupamos de la simulación numérica de la dinámica glaciar. Presentamos el modelo físico-matemático utilizado, discutimos sus condiciones de contorno y cómo éstas se miden en los trabajos de campo, y describimos el procedimiento de resolución numérica del sistema de ecuaciones parciales del modelo. Presentamos los resultados para los campos de velocidades, deformaciones y tensiones, comparando estos resultados con las estructuras observadas. También incluimos el análisis de las elipses de deformación acumulativa, que proporcionan información sobre las estructuras a las que puede dar lugar la evolución del estado de deformaciones y tensiones a las que se ve sometido el hielo según avanza, lentamente, desde la cabecera hasta la zona terminal del glaciar, con tiempos de tránsito de hasta 1.250 años, recogiendo así la historia de deformaciones en el glaciar. Concluyendo, ponemos de manifiesto en esta tesis que las medidas de campo de las estructuras y niveles de cenizas, las medidas de georradar y las simulaciones numéricas de la dinámica glaciar, realizadas de forma combinada, permiten caracterizar el régimen actual de velocidades, deformaciones y tensiones del glaciar, entender su evolución en el pasado y predecir su evolución futura. ABSTRACT The main objective of this thesis is to characterize the morphology and the state of strains and stresses of Hurd Glacier (Livingston Island, South Shetland Islands archipelago, Antarctica) through a combination of field observations, ground-penetrating radar measurements and numerical simulations. The morphology and the current state of strain and stresses are the expression of the dynamic evolution of the glacier from the past to recent times, and their analysis gives us the guidelines to be able to predict, with the support of numerical simulations, its future evolution. The first subject addressed is the study of structures that can be observed on the glacier surface. We describe the different techniques used (field measurements, photointerpretation of orthophotos, geochemical analysis of volcanic ashes, etc.) and we present the analysis and interpretation of the morpho-structural results, as well as the correlation with geochemical analysis (XRF) between the volcanic ashes extruded to the surface of Hurd Glacier and those of Deception Island volcano, from which the ashes originate. This allows us dating the ashes as Tephra 1, corresponding to the 1970 eruption, Tephra 2, corresponding to the pre-1829 eruptions, and the Tephra 3 group, associated with older eruptions. Secondly we focus on the study of the structures present within the glacier, which are detected with the help of ground-penetrating radar. Once identified, we link these internal structures with those observed on the glacier surface. We also study the hydrothermal structure of the glacier, getting a series of additional evidences of its polythermal structure. Among the evidences available so far, we can mention those based on the value of the stiffness parameter of the constitutive relation of ice, determined by fitting dynamic models to observations, as done by Otero (2008), and those based on the velocity of propagation of the radar waves through the glacier ice, measured using the common midpoint method, as done by Navarro et al. (2009). The additional evidences that we provide in this thesis are: 1) the presence of structures typical of compressive regime in the terminal zone of the glacier, together with shear at its margins, and 2) the presence of a surface layer of cold ice (overlying a layer of temperate ice) in the ablation zone of the three lobes of Hurd Glacier –Sally Rocks, Argentina and Las Palmas–, reaching thicknesses of 70, 50 and 40 m, respectively. This cold layer is probably frozen to the subglacial bed in the terminal zone (Molina and others 2007; this thesis). Finally, we deal with the numerical simulation of glacier dynamics. We present the physical-mathematical model, discuss its boundary conditions and how they are measured in the field work, and describe the method of numerical solution of the model’s partial differential equations. We present the results for the velocity, strain and stress fields, comparing these results with the observed structures. We also include an analysis of the ellipses of cumulative deformation, which provide information about the structures that can result from the evolution of the strain and stress regime of the glacier ice as it moves slowly from the head to the snout of the glacier, with transit times of up to 1,250 years, so picking the history of deformation of the glacier. Summarizing, we show in this thesis that field measurements of structures and ash layers, ground-penetrating radar measurements and numerical simulations of glacier dynamics, performed in combination, allow us to characterize the current regime of velocities, strains and stresses of the glacier, to understand its past evolution and to predict its future evolution.

Surface velocity and mass balance of Livingston Island ice cap, Antarctica

The mass budget of the ice caps surrounding the Antarctica Peninsula and, in particular, the partitioning of its main components are poorly known. Here we approximate frontal ablation (i.e. the sum of mass losses by calving and submarine melt) and surface mass balance of the ice cap of Livingston Island, the second largest island in the South Shetland Islands archipelago, and analyse variations in surface velocity for the period 2007–2011. Velocities are obtained from feature tracking using 25 PALSAR-1 images, and used in conjunction with estimates of glacier ice thicknesses inferred from principles of glacier dynamics and ground-penetrating radar observations to estimate frontal ablation rates by a flux-gate approach. Glacier-wide surface mass-balance rates are approximated from in situ observations on two glaciers of the ice cap. Within the limitations of the large uncertainties mostly due to unknown ice thicknesses at the flux gates, we find that frontal ablation (−509 ± 263 Mt yr−1, equivalent to −0.73 ± 0.38 m w.e. yr−1 over the ice cap area of 697 km2) and surface ablation (−0.73 ± 0.10 m w.e. yr−1) contribute similar shares to total ablation (−1.46 ± 0.39 m w.e. yr−1). Total mass change (δM = −0.67 ± 0.40 m w.e. yr−1) is negative despite a slightly positive surface mass balance (0.06 ± 0.14 m w.e. yr−1). We find large interannual and, for some basins, pronounced seasonal variations in surface velocities at the flux gates, with higher velocities in summer than in winter. Associated variations in frontal ablation (of ~237 Mt yr−1; −0.34 m w.e. yr−1) highlight the importance of taking into account the seasonality in ice velocities when computing frontal ablation with a flux-gate approach.