Berlin, Humboldt-Universiẗat, Diss., 2004.

Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Dec. 2, 2009). Includes bibliographical references.

In this study, near-surface stratigraphy was measured in snowpits and shallow ice cores across all snow facies of a High Arctic ice cap in order to examine variability at different spatial (metre to &gt; kilometre) and temporal (seasonal and inter-annual) resolutions.  Additionally, dye tracing was employed to investigate processes controlling meltwater percolation and refreezing.  <i>Pre-melt </i>snowpack densities were low at all spatial scales, whilst different inter-annual <i>post-melt </i>stratigraphies at &gt; 1 km scales showed high variability.  This is attributed to different extrinsic conditions generating dissimilar surface melt and percolation regimes.  Variability at small spatial scales is related to the intrinsic stratigraphic properties of the pre-melt snowpack. A snowpack model was applied to a single point at 1400 m.a.s.l. over the course of two summers, to assess its simulation of the observed dissimilar annular density evolution. The model performed poorly due to an inability to simulate ice layers in the near surface snowpack, which are the main property controlling variability.  Modelled thermal regimes and densification were also unrealistic and found to be highly sensitive to albedo.  The model may be improved by incorporating diurnal Albedo variations; known to be a strong control on surface melting at high latitudes. Overall, combined <i>in-situ</i> measurements and modelling results show that the relationship between near-surface densification and air temperature is not straightforward.  Extrapolation of generalised trends between the two, across large spatial and temporal scales, should be avoided since spatial and temporal variability can be high.  This should be considered when up-scaled modelling of surface mass balance and firm densification is utilised during interpretations of SRA-based estimates of elevation change across large ice masses over several years.

This investigation focuses on two well-preserved impact structures developed in sedimentary target rocks: the ~23.5 Ma old Haughton structure, Canada, and the ~14.5 Ma old Ries structure, Germany. The aim of this study was to investigate the effects of hypervelocity impact into sedimentary targets. The study reveals that a series of different impactites are present at Haughton, the bulk of which comprise a groundmass of impact-generated melts (calcite + silicate glass ± anhydrite). Thus, carbonates, evaporites, sandstones, and shales underwent shock melting during the Haughton impact event. The shock melting of impure carbonates resulted in the generation of Mg–Ca–Si-rich melts that crystallized calcite during rapid cooling. The residual melt quenched to Mg–Si-rich glass. These impactites should, therefore, be classified as clast-rich impact melt rocks or impact melt breccias, and not clastic matrix breccias as previously held. Ries surficial suevites are reinterpreted as clast-rich impact melt rocks or impact melt breccias. Four main types of impact melt glass are present, in contrast to previous studies that recognized only one type. These results are at odds with the current, generally accepted, definition of suevite. Given that the Ries is the original type occurrence of ‘suevite’, some redefinition of the term suevite may be in order. Furthermore, it is clear that sedimentary rocks, as well as crystalline rocks, were shock melted during the Ries impact event. The results of this study are, therefore, incompatible with previous models in which the zone of melting is restricted to the crystalline basement. It is apparent that impact melting in sedimentary targets is much more common than previously thought. Furthermore, there is no unequivocal evidence for the decomposition of carbonates or evaporites at any terrestrial impact site. Many previous assumptions about the response of sedimentary rocks during hypervelocity impact events are, therefore, incorrect. The products of impact into sedimentary targets may appear very different from those developed in crystalline targets. However, microscopic imaging and analysis suggests that these seemingly different lithologies may be genetically equivalent. Thus, the apparent ‘anomaly’ between the amount of impact melt rocks formed in sedimentary and crystalline targets may be due to a misinterpretation of the rock record.

Glacier facies represent distinct regions of a glacier surface characterized by near surface structure and density that develop as a function of spatial variations in surface melt and accumulation. In post freeze-up (autumn) synthetic aperture radar (SAR) satellite imagery, the glacier ice zone and dry snow zone have a relatively low backscatter due to the greater penetration of the radar signal into the surface. Conversely, the saturation and percolation zones are identifiable based on their high backscatter due to the presence of ice lenses and pipes acting as efficient scatterers. In this study, EnviSat ASAR imagery is used to monitor the progression of facies zones across Devon Ice Cap (DIC) from 2004 to 2011. This data is validated against in situ surface temperatures, mass balance data, and ground penetrating radar surveys from the northwest sector of DIC. Based on calibrated (sigma nought) EnviSat ASAR backscatter values, imagery from autumn 2004 to 2011 shows the disappearance of the ‘pseudo’ dry snow zone at high elevations, the migration of the glacier and superimposed ice zones to higher elevations, and reduction in area of the saturation/percolation zone. In 2011, the glacier and superimposed ice zone were at their largest extent, occupying 92% of the ice cap, leaving the saturation/percolation zone at 8% of the total area. This is indicative of anomalously high summer melt and strongly negative mass balance conditions on DIC, which results in the infilling of pore space in the exposed firn and consequent densification of the ice cap at higher elevations.

Glacier facies represent distinct regions of a glacier surface characterized by near surface structure and density that develop as a function of spatial variations in surface melt and accumulation. In post freeze-up (autumn) synthetic aperture radar (SAR) satellite imagery, the glacier ice zone and dry snow zone have a relatively low backscatter due to the greater penetration of the radar signal into the surface. Conversely, the saturation and percolation zones are identifiable based on their high backscatter due to the presence of ice lenses and pipes acting as efficient scatterers. In this study, EnviSat ASAR imagery is used to monitor the progression of facies zones across Devon Ice Cap (DIC) from 2004 to 2011. This data is validated against in situ surface temperatures, mass balance data, and ground penetrating radar surveys from the northwest sector of DIC. Based on calibrated (sigma nought) EnviSat ASAR backscatter values, imagery from autumn 2004 to 2011 shows the disappearance of the ‘pseudo’ dry snow zone at high elevations, the migration of the glacier and superimposed ice zones to higher elevations, and reduction in area of the saturation/percolation zone. In 2011, the glacier and superimposed ice zone were at their largest extent, occupying 92% of the ice cap, leaving the saturation/percolation zone at 8% of the total area. This is indicative of anomalously high summer melt and strongly negative mass balance conditions on DIC, which results in the infilling of pore space in the exposed firn and consequent densification of the ice cap at higher elevations.

A 147cm sediment core from Lake DV09, northern Devon Island, Nunavut, Canada (75° 34’34”N, 89° 18’55”W) contains annually-laminated (varved) sediments, providing a 1600-year record of climate variability. A minerogenic lamina deposited during the annual thaw period and a thin deposit of organic matter deposited during the summer and through the winter, together form a clastic-organic couplet each year. The thinnest varves occur from AD800-1050, and the thickest from AD1100-1300, during the Medieval Warm Period. The relative sediment density is also highest during this period suggesting increased sediment transport energy. The coldest period of the Little Ice Age appears to be during the AD1600s. Varve widths over the past century indicate climate warming in the region. / This research program was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS). A tuition bursary from Ultramar Inc. also helped in making this research possible. Logistical support was provided by the Polar Continental Shelf Project (PCSP Contribution number 04508).

A 147cm sediment core from Lake DV09, northern Devon Island, Nunavut, Canada (75° 34’34”N, 89° 18’55”W) contains annually-laminated (varved) sediments, providing a 1600-year record of climate variability. A minerogenic lamina deposited during the annual thaw period and a thin deposit of organic matter deposited during the summer and through the winter, together form a clastic-organic couplet each year. The thinnest varves occur from AD800-1050, and the thickest from AD1100-1300, during the Medieval Warm Period. The relative sediment density is also highest during this period suggesting increased sediment transport energy. The coldest period of the Little Ice Age appears to be during the AD1600s. Varve widths over the past century indicate climate warming in the region. / This research program was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS). A tuition bursary from Ultramar Inc. also helped in making this research possible. Logistical support was provided by the Polar Continental Shelf Project (PCSP Contribution number 04508).

A 147cm sediment core from Lake DV09, northern Devon Island, Nunavut, Canada (75° 34’34”N, 89° 18’55”W) contains annually-laminated (varved) sediments, providing a 1600-year record of climate variability. A minerogenic lamina deposited during the annual thaw period and a thin deposit of organic matter deposited during the summer and through the winter, together form a clastic-organic couplet each year. The thinnest varves occur from AD800-1050, and the thickest from AD1100-1300, during the Medieval Warm Period. The relative sediment density is also highest during this period suggesting increased sediment transport energy. The coldest period of the Little Ice Age appears to be during the AD1600s. Varve widths over the past century indicate climate warming in the region. / This research program was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS). A tuition bursary from Ultramar Inc. also helped in making this research possible. Logistical support was provided by the Polar Continental Shelf Project (PCSP Contribution number 04508).

A 147cm sediment core from Lake DV09, northern Devon Island, Nunavut, Canada (75° 34’34”N, 89° 18’55”W) contains annually-laminated (varved) sediments, providing a 1600-year record of climate variability. A minerogenic lamina deposited during the annual thaw period and a thin deposit of organic matter deposited during the summer and through the winter, together form a clastic-organic couplet each year. The thinnest varves occur from AD800-1050, and the thickest from AD1100-1300, during the Medieval Warm Period. The relative sediment density is also highest during this period suggesting increased sediment transport energy. The coldest period of the Little Ice Age appears to be during the AD1600s. Varve widths over the past century indicate climate warming in the region. / This research program was funded by the Natural Sciences and Engineering Research Council of Canada (NSERC), and the Canadian Foundation for Climate and Atmospheric Sciences (CFCAS). A tuition bursary from Ultramar Inc. also helped in making this research possible. Logistical support was provided by the Polar Continental Shelf Project (PCSP Contribution number 04508).