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No description available.

No description available.

The Darwin-Hatherton glacial system (DHGS) drains from the East Antarctic Ice Sheet (EAIS) and through the Transantarctic Mountains (TAM) before entering the Ross Embayment. Large ice-free areas covered in glacial sediments surround the DHGS, and at least five glacial drift sheets mark the limits of previous ice extent. The glacier belongs to a group of slow-moving EAIS outlet glaciers which are poorly understood. Despite this, an extrapolation of a glacial drift sheet boundary has been used to determine the thickness of the EAIS and the advanced West Antarctic Ice Sheet (WAIS) during the Last Glacial Maximum (LGM). In order to accurately determine the past and present contributions of the Antarctic ice sheets to sea level changes, these uncertainties should be reduced. This study aims to examine the present and LGM ice dynamics of the DHGS by combining newly acquired field measurements with a 3-D numerical ice sheet-shelf model. The fieldwork included a ground penetrating radar survey of ice thickness and surface velocity measurements by GPS. In addition, an extensive dataset of airborne radar measurements and meteorological recordings from automatic weather stations were made available. The model setup involved nesting a high-resolution (1 km) model of the DHGS within a lower resolution (20 km) all-Antarctic simulation. The nested 3-D modelling procedure enables an examination of the impact of changes of the EAIS and WAIS on the DHGS behaviour, and accounts for a complex glacier morphology and surface mass balance within the glacial system. The findings of this study illustrate the difference in ice dynamics between the Darwin and Hatherton Glaciers. The Darwin Glacier is up to 1500 m thick, partially warm-based, has high driving stresses (~150 kPa), and measured ice velocities increase from 20-30 m yr⁻¹ in the upper parts to ~180 m yr⁻¹ in the lowermost steepest regions, where modelled flow velocities peak at 330 m yr⁻¹. In comparison, the Hatherton Glacier is relatively thin (<900 m), completely cold-based, has low driving stresses (~85 kPa), and is likely to flow with velocities <10 m yr⁻¹ in most regions. It is inferred that the slow velocities with which the DHGS flows are a result of high subglacial mountains restricting ice flow from the EAIS, large regions of frozen basal conditions, low SMB and undulating bedrock topography. The model simulation of LGM ice conditions within the DHGS implies that the ice thickness of the WAIS has been significantly overestimated in previous reconstructions. Results show that the surface of the WAIS and EAIS away from the TAM would have been elevated 600-750 and 0-80 m above present-day levels, respectively, for the DHGS to reach what was inferred to represent the LGM drift sheet limit. Ultimately, this research contributes towards a better understanding of the dynamic behaviour of slow moving TAM outlet glaciers, and provides new insight into past changes of the EAIS and WAIS. This will facilitate more accurate quantifications of contributions of the WAIS and EAIS to changes in global sea level.

Glacial isostatic adjustment (GIA) is the process by which the solid Earth responds to past and present-day changes in glaciers, ice caps, and ice sheets. This thesis focuses on vertical crustal motion of the Earth caused by GIA, which is influenced by several factors including lithosphere thickness, mantle viscosity profile, and changes to the thickness and extent of surface ice. The viscosity of the mantle beneath Antarctica is a poorly constrained quantity due to the rarity of relative sea-level and heat flow observations. Other methods for obtaining a better-constrained mantle viscosity model must be investigated to obtain more accurate GIA model predictions. The first section of this study uses seismic wave tomography to determine mantle viscosity. By calculating the deviation of the P- and S-wave velocities relative to a reference Earth model (PREM), the viscosity can be determined. For Antarctica mantle viscosities obtained from S20A (Ekstrom and Dziewonski, 1998) seismic tomography in the asthenosphere range from 1016 Pa∙s to 1023 Pa∙s, with smaller viscosities beneath West Antarctica and higher viscosities beneath East Antarctica. This agrees with viscosity expectations based on findings from the Basin and Range area of North America, which is an analogue to the West Antarctic Rift System. Section two compares bedrock elevations in Antarctica to crustal thicknesses, to infer mantle temperatures and draw conclusions about mantle viscosity. Data from CRUST 2.0 (Bassin et al., 2000), BEDMAP (Lythe and Vaughan, 2001) and specific studies of crustal thickness in Antarctica were examined. It was found that the regions of Antarctica that are expected to have low viscosities agree with the hot mantle trend found by Hyndman (2010) while the regions expected to have high viscosity are in better agreement with the trend for cold mantle. Bevis et al. (2009) described new GPS observations of crustal uplift in Antarctica and compared the results to GIA model predictions, including IJ05 (Ivins and James, 2005). Here, we have generated IJ05 predictions for a three layered mantle (viscosities ranging over more than four orders of magnitude) and compared them to the GPS observations using a χ2 measure of goodness-of-fit. The IJ05 predictions that agree best with the Bevis et al. observations have a χ2 of 16, less than the null hypothesis value of 42. These large values for the best-fit model indicate the need for model revisions and/or that uncertainties are too optimistic. Equally important, the mantle viscosities of the best-fit models are much higher than expected for West Antarctica. The smallest χ2 values are found for an asthenosphere viscosity of 1021 Pa•s, transition zone viscosity of 1023 Pa∙s and lower mantle viscosity of 2 x 1023 Pa∙s, whereas the expected viscosity of the asthenosphere beneath West Antarctica is probably less than 1020 Pa∙s. This suggests that revisions to the IJ05 ice sheet history are required. Simulated annealing was performed on the ice sheet history and it was found that changes to the recent ice load history have the strongest effect on GIA predictions. / Graduate

We investigate the silicon (Si) cycle in the Southern Ocean through two isotopic approaches: (1) 30Si-incubation experiments and (2) natural silicon isotopic composition (ä30Si). 30Si-spiked incubation allows to discriminate the short-term (~ 1 day) net Si-uptake flux in bSiO2 production and dissolution. ä30Si of both biogenic silica and dissolved silicon integrates at seasonal/annual scale bSiO2 production or dissolution and mixing.<p>(1) A new mass spectrometer method (HR-SF-ICPMS) has been developed for 30Si-isotopic abundance measurements. This methodology is faster and easier than the previous available methodologies and has the same precision. A complete set of incubation was coupled with parallel 32Si-incubations and the two methodologies give not significantly different bSiO2 production rates. In the Southern Ocean, especially in the southern Antarctic Circumpolar Current, the large silicic acid concentration degrades the sensitivity of the method with Si dissolution fluxes staying generally below the detection limit. In contrast, the 28Si-isotopic dilution was sensitive enough to assess low biogenic silica dissolution rates in silicic acid poor waters of the northern ACC. We show that large accumulation of detrital dissolving biogenic silica after productive period implies really efficient silicon loop with integrated (euphotic layer) dissolution:production ratio equal or larger than 1.<p> (2) We largely expand the silicic acid isotopic data in the open ocean. Relatively simple mass and isotopic balances have been performed in the Antarctic Zone and have allowed to apply for the first time ä30Si in a quantitative way to estimate regional net silica production and quantify source waters fueling bSiO2 productivity. We observe that at the end of the productive period as suggested with 30Si-incubation, large accumulation of detrital biogenic silica in the surface waters increase the D:P ratio and subsequently dampens the bSiO2 production mediated isotopic fractionation with residual biogenic silica carrying heavier ä30Si than expected. Seasonal isotopic evolution is simulated and seems in agreement with our observations. These simulations strongly suggest working with non-zero order equations to fully assess the seasonal expression of the different processes involved: mixing, uptake, dissolution. Si-isotopes are also tracking the origin and fates of the different ACC pools across the Southern Ocean meridional circulation. Moreover during the circumpolar eastward pathway, the bSiO2 dissolution in deep water decreases the corresponding ä30Si values and this imprint is further transmitted via the upper limb of the meridional circulation in the intermediate water masses.<p> / Doctorat en Sciences / info:eu-repo/semantics/nonPublished

Thesis (MComm)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The Southern Ocean is a complex system, where the relationship between CO2 concentrations and its drivers varies intra- and inter-annually. Due to the lack of readily available in situ data in the Southern Ocean, a model approach was required which could predict the CO2 concentration proxy variable, fCO2. This must be done using predictor variables available via remote measurements to ensure the usefulness of the model in the future. These predictor variables were sea surface temperature, log transformed chlorophyll-a concentration, mixed layer depth and at a later stage altimetry. Initial exploratory analysis indicated that a non-parametric approach to the model should be taken. A parametric multiple linear regression model was developed to use as a comparison to previous studies in the North Atlantic Ocean as well as to compare with the results of the non-parametric approach. A non-parametric kernel regression model was then used to predict fCO2 and nally a combination of the parametric and non-parametric regression models was developed, referred to as the mixed regression model. The results indicated, as expected from exploratory analyses, that the non-parametric approach produced more accurate estimates based on an independent test data set. These more accurate estimates, however, were coupled with zero estimates, caused by the curse of dimensionality. It was also found that the inclusion of salinity (not available remotely) improved the model and therefore altimetry was chosen to attempt to capture this e ect in the model. The mixed model displayed reduced errors as well as removing the zero estimates and hence reducing the variance of the error rates. The results indicated that the mixed model is the best approach to use to predict fCO2 in the Southern Ocean and that altimetry's inclusion did improve the prediction accuracy. / AFRIKAANSE OPSOMMING: Die Suidelike Oseaan is 'n komplekse sisteem waar die verhouding tussen CO2 konsentrasies en die drywers daarvoor intra- en interjaarliks varieer. 'n Tekort aan maklik verkrygbare in situ data van die Suidelike Oseaan het daartoe gelei dat 'n model benadering nodig was wat die CO2 konsentrasie plaasvervangerveranderlike, fCO2, kon voorspel. Dié moet gedoen word deur om gebruik te maak van voorspellende veranderlikes, beskikbaar deur middel van afgeleë metings, om die bruikbaarheid van die model in die toekoms te verseker. Hierdie voorspellende veranderlikes het ingesluit see-oppervlaktetemperatuur, log getransformeerde chloro l-a konsentrasie, gemengde laag diepte en op 'n latere stadium, hoogtemeting. 'n Aanvanklike, ondersoekende analise het aangedui dat 'n nie-parametriese benadering tot die data geneem moet word. 'n Parametriese meerfoudige lineêre regressie model is ontwikkel om met die vorige studies in die Noord-Atlantiese Oseaan asook met die resultate van die nieparametriese benadering te vergelyk. 'n Nie-parametriese kern regressie model is toe ingespan om die fCO2 te voorspel en uiteindelik is 'n kombinasie van die parametriese en nie-parametriese regressie modelle ontwikkel vir dieselfde doel, wat na verwys word as die gemengde regressie model. Die resultate het aangetoon, soos verwag uit die ondersoekende analise, dat die nie-parametriese benadering meer akkurate beramings lewer, gebaseer op 'n onafhanklike toets datastel. Dié meer akkurate beramings het egter met "nul"beramings gepaartgegaan wat veroorsaak word deur die vloek van dimensionaliteit. Daar is ook gevind dat die insluiting van soutgehalte (nie beskikbaar oor via sateliet nie) die model verbeter en juis daarom is hoogtemeting gekies om te poog om hierdie e ek in die model vas te vang. Die gemengde model het kleiner foute getoon asook die "nul"beramings verwyder en sodoende die variasie van die foutkoerse verminder. Die resultate het dus aangetoon dat dat die gemengde model die beste benadering is om te gebruik om die fCO2 in die Suidelike Oseaan te beraam en dat die insluiting van altimetry die akkuraatheid van hierdie beraming verbeter.

Satellite investigations have documented Antarctic sea ice area, but are restricted in their ability to provide volume, as the procedure to derive thickness is still under development. This procedure requires the measurement of sea ice freeboard, the segment of ice held above the ocean surface by buoyancy. This measurement can be made by satellite altimeters and in conjunction with density and snow depth information; sea ice thickness can be estimated via the hydrostatic equilibrium assumption. The ability to monitor the spatial and temporal characteristics of the thickness distribution must be improved as we strive to understand the linkages between the glaciological, atmospheric and oceanic components of the Antarctic climate system. A key sector in which these components interact is the Antarctic coast. There, offshore winds drive coastal polynyas creating vast amounts of sea ice, and ice shelf interaction modifies ocean properties. Together they condition the ocean for downwelling, driving the global oceanic circulation. In light of this, the coastal Antarctic is a fundamental region in regard to Antarctic sea ice processes and the Earth climate system. McMurdo Sound occupies a coastal area in proximity to an ice shelf in the south-western corner of the Ross Sea. The sound has witnessed scientific investigation for over a century with a fully established research programme since the 1960s. However, the sea ice research in this region is spatially restricted. This thesis aims to expand the knowledge of sea ice in McMurdo Sound to a larger area using space-borne remote sensing instrumentation and design of in situ measurement campaigns. In doing so, this work evaluates the capabilities of satellite platforms to record sea ice freeboard in the coastal Antarctic, whilst developing knowledge of ice shelf-sea ice interaction. This work provides the first satellite altimeter based investigation of sea ice freeboard in McMurdo Sound using ICESat over the period 2003-2009. No observable trend was observed for first-year sea ice freeboard in the region in line with larger scale assessments in the Ross Sea. However, there was significant increase in the freeboard of a temporary multiyear sea ice regime, the segment of the largest increase linked to the outflow of supercooled Ice Shelf Water (ISW) from the McMurdo and Ross Ice Shelf cavities. This remote sensing assessment supports the in situ and modelling work of many others who have identified the influence of ISW on sea ice processes in this region, in particular, that it is thicker than it would otherwise be. The influence of ISW on altimetric sea ice thickness retrievals was also quantified using a Global Navigation Satellite System (GNSS) evaluation of freeboard to thickness conversion. This revealed that a sub-ice platelet layer, created by supercooled ISW and with an estimated solid fraction of 0.16, accumulates beneath the sea ice cover and influences the thickness estimates from the GNSS-derived surface elevation. A cautionary conclusion is reached that within 100 km of ice shelves this buoyant influence should be considered, and in close proximity (< 50 km) can result in overestimations of sea ice thickness of ~ 12 %. It is also suggested that the sea ice freeboard anomalies that result from enhanced growth, driven by supercooled water advection could be used to map the presence of ISW in the coastal Antarctic. Looking to future ability to monitor Southern Ocean sea ice thickness from space, the first comprehensive evaluation of CryoSat-2 (CS-2) over Antarctic sea ice is provided. Using three separate retracking procedures, CS-2 is shown to be capable of detecting the development of a fast ice cover in McMurdo Sound. The role played by a snow cover with layering typical of the Antarctic appears to cause a positive bias in the ice freeboard for a waveform fitting procedure currently used over Arctic sea ice. The identification of open water and the establishment of accurate sea surface heights are also indicated as causing errors (in the order of cms) in the study region. CS-2 is shown to be capable of recording sea ice growth over two growth cycles in McMurdo Sound. This work has advanced the application of satellite investigative techniques to Antarctic sea ice, providing hope that such techniques may be capable of revealing larger scale connections between sea ice and ice shelves.

The Legal regime of Antarctica, primarily the protection of its environment and the position of the Czech Republic The purpose of my thesis is to analyse a legal regime of Antarctica, with regards to protection of its environment and position of the Czech Republic. The thesis is divided into four chapters. Chapter One contains basic introduction of the Antarctic Continent, its geography and history. Chapter Two investigates legal regime constituted in Antarctica by the Antarctic Treaty and other international documents, known as the Antarctic Treaty System. This chapter consists of six parts, each concentrating on special subject. Part one examines the path of development the Antarctic treaty, part two deals with treaty itself, part three looks at dispute settlement, part four focuses on liability in this international space, part five addresses the issue of inspections held in Antarctica. Part six describes structure and organisation of the Antarctic Treaty System, Antartic Treaty Consultative Meetings, its legal documents and Secretariat of the Antarctic Treaty. Chapter Three concentrates on the problem of protection of antarctic environment. Firts part of this chapter focuses on protection of living resources, guaranteed by the Convention for the Conservation of Antarctic Seals and the...