Dissertations / Theses on the topic 'McMurdo Sound'

Reactive halogen species (RHS) are responsible for ozone depletion and oxidation of gaseous elemental mercury and dimethyl sulphide in the polar boundary layer, but the sources and mechanisms controlling their catalytic reaction cycles are still not completely understood. To further investigate these processes, ground– based Multi–Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations of boundary layer BrO and IO were made from a portable instrument platform in McMurdo Sound during the Antarctic spring of 2006 and 2007. Measurements of surface ozone, temperature, pressure, humidity, and wind speed and direction were also made, along with fourteen tethersonde soundings and the collection of snow samples for mercury analysis. A spherical multiple scattering Monte Carlo radiative transfer model (RTM) was developed for the simulation of box-air-mass-factors (box-AMFs), which are used to determine the weighting functions and forward model differential slant column densities (DSCDs) required for optimal estimation. The RTM employed the backward adjoint simulation technique for the fast calculation of box-AMFs for specific solar zenith angles (SZA) and MAX-DOAS measurement geometries. Rayleigh and Henyey-Greenstein scattering, ground topography and reflection, refraction, and molecular absorption by multiple species were included. Radiance and box-AMF simulations for MAX-DOAS measurements were compared with nine other RTMs and showed good agreement. A maximum a posteriori (MAP) optimal estimation algorithm was developed to retrieve trace gas concentration profiles from the DSCDs derived from the DOAS analysis of the measured absorption spectra. The retrieval algorithm was validated by performing an inversion of artificial DSCDs, simulated from known NO2 profiles. Profiles with a maximum concentration near the ground were generally well reproduced, but the retrieval of elevated layers was less accurate. Retrieved partial vertical column densities (VCDs) were similar to the known values, and investigation of the averaging kernels indicated that these were the most reliable retrieval product. NO₂ profiles were also retrieved from measurements made at an NO₂ measurement and profiling intercomparison campaign in Cabauw, Netherlands in July 2009. Boundary layer BrO was observed on several days throughout both measurement periods in McMurdo Sound, with a maximum retrieved surface mixing ratio of 14.4±0.3 ppt. The median partial VCDs up to 3km were 9.7±0.07 x 10¹² molec cm ⁻ in 2007, with a maximum of 2.3±0.07 x 10¹³ molec cm⁻², and 7.4±0.06 x 10¹² molec cm⁻² in 2006, with a maximum of 1.05 ± 0.07 x 1013 molec cm⁻². The median mixing ratio of 7.5±0.5 ppt for 2007 was significantly higher than the median of 5.2±0.5 ppt observed in 2006, which may be related to the more extensive first year sea ice in 2007. These values are consistent with, though lower than estimated boundary layer BrO concentrations at other polar coastal sites. Four out of five observed partial ozone depletion events (ODEs) occurred during strong winds and blowing snow, while BrO was present in the boundary layer in both stormy and calm conditions, consistent with the activation of RHS in these two weather extremes. Air mass back trajectories, modelled using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model, indicated that the events were locally produced rather than transported from other sea ice zones. Boundary layer IO mixing ratios of 0.5–2.5±0.2 ppt were observed on several days. These values are low compared to measurements at Halley and Neumayer Stations, as well as mid-latitudes. Significantly higher total mercury concentrations observed in 2007 may be related to the higher boundary layer BrO concentrations, but further measurements are required to verify this.

This project explored the potential fate and transport of seawater-based drilling fluid used in the Antarctic Drilling Program (ANDRILL) South McMurdo Sound project (SMS). The SMS drilling reported a loss of 5.6 × 10 ⁵ liters of drilling fluid to the surrounding formation throughout a borehole depth of 1139m. The introduction of these drilling fluids raise concerns of potential contamination to a pristine, isolated environment. The volume of fluid lost to the subsurface is unrecoverable and will only break down through natural attenuation processes, such as biodegradation. The objectives of this study are to estimate the extent of fluid migration laterally from the borehole and to determine when biodegradation of the water-based drilling fluid is effectively occurring. Variable density groundwater flow modeling (SEAWAT) was used to simulate the environment around the borehole. Applying stresses similar to the drilling events produced an estimate of how far fluid will be transported as drilling fluid is being circulated. Results show the fluid to migrate up to 7.5m into the subsurface. Additionally, laboratory microcosms were set up to incubate drilling fluid samples at various temperatures (5, 25, and 50°C) under aerobic and anaerobic conditions. Experimental data collected over 188 days was analyzed to evaluate the time frame when biodegradation of drilling fluids occurred. Carbon isotope fractionation ( ¹³C/¹²C) was used to determine the ability of the drilling fluids to be used as a food source. Biological data observed changes in microbial growth using DNA quantification, and changes in microbial communities using Biolog EcoPlates™. Results show a positive correlation between the increase of δ¹³C (‰) values and an increase in DNA (ng/µl) quantity. Data from geochemical and community changes indicate biodegradation of the drilling fluid occurred between time 40 and time 100. The methods employed to investigate fate and transport is a unique approach, and applied to these water-based drilling fluids for the first time in this study.

A soil climate monitoring network, consisting of seven automated weather stations, was established between 1999 and 2003 in the McMurdo Sound region of Antarctica. Soil temperature, soil water content, air temperature, relative humidity, solar radiation, and wind speed and direction are recorded hourly and downloaded annually. Two 30 m deep permafrost temperature monitoring boreholes were established adjacent to the soil climate stations in the Wright Valley and at Marble Point in January 2007. Sixteen thermistors (accurate to ±0.1°C) were installed in each borehole measuring temperature once every hour and recording the mean every six hours. One year of permafrost temperatures were available (January 2007 to January 2008). The overall aim of this thesis was to make use of the soil climate monitoring database from 1999 to 2007 to investigate Antarctic soil climate. Active layer depth (depth of thawing) varied inter-annually, with no significant trend between 1999 and 2007. The active layer increased with decreasing latitude (R2 = 0.94), and decreased with increasing altitude (R2 = 0.95). A multiple regression model was produced whereby active layer depth was predicted as a function of mean summer air temperature, mean winter air temperature, total summer solar radiation and mean summer wind speed (R2 = 0.73). Annual temperature cycles were observed at all depths in the boreholes. At Marble Point, an annual temperature range of lt;1°C occurred at 15.2 m, lt;0.5°C at 18.4 m and lt;0.1°C at 26.4 m and at Wright Valley, an annual temperature range of lt;1°C occurred at 14.0 m, lt;0.5°C at 17.2 m and lt;0.1°C at 25.2 m. Given that the depth of Zero Annual Amplitude determined depends on the sensitivity of the measurement method, it is suggested that instead of referring to a depth of Zero Annual Amplitude , the depth at which the annual temperature range is less than a given value is a more useful concept. Mean annual and mean seasonal air and soil temperatures varied inter-annually and there was no significant trend of warming or cooling over the 1999 - 2007 period. Mean annual air temperatures were primarily influenced by winter air temperatures. Mean annual and mean summer soil temperatures were warmer than air temperatures due to heating by solar radiation. Mean summer air temperatures correlated well with the Southern Annular Mode Index (SAMI) at all sites (0.61 lt; R2 lt; 0.73) except Victoria Valley; however there was no correlation between mean annual or mean winter temperatures and the SAMI. Air temperature was linearly correlated with near-surface soil temperature (1.3 - 7.5 cm) (R2 gt; 0.79). Near-surface soil temperature was strongly correlated with incoming solar radiation at Victoria Valley (0.14 lt; R2 lt; 0.76) and Granite Harbour (0.49 lt; R2 lt; 0.82), but was not significantly correlated at other sites (0 lt; R2 lt; 0.57). There was no significant correlation between air temperature and wind speed, air temperature and solar radiation and near-surface soil temperature and wind speed, despite occasions of strong correlation on the diurnal time scale. Diurnal summer cycles in air and soil temperatures were driven by solar radiation. Multiple regressions combining the effects of air temperature, solar radiation and wind speed approximated near-surface soil temperatures well at every site during both summer and winter (0.88 lt; R2 lt; 0.98).

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
A variedade de ecossistemas microbianos que existe na Antártica representa uma oportunidade extraordinária para pesquisas sobre a ecologia, diversidade e evolução microbiana, principamente em termos de cianobactéria. Neste trabalho, foi avaliado o papel de atributos ambientais no controle da montagem de esteiras microbianas antárticas. Inicialmente foi caracterizado a diversidade cianobacteriana das esteiras ao longo de gradientes ambientais na região do McMurdo Sound, Antártica continental. Em seguida, foi avaliado o papel das variáveis ambientais na determinação da composição da assembléia de cianobactérias através da análise de amostras de água e esteiras de cianobactérias microbianas de 25 lagos distribuídos em quatro distintas áreas geográficas: McMurdo Ice Shelf, Ross Island e Upper e Lower Wright Valleys. Finalmente, foi realizado experimentos de laboratório para determinar a extensão com que a composição de espécies afeta a formação das esteiras microbianas. Vinte e nove morfoespécies foram identificadas e descritas no capítulo 1. Quatro foram designadas à ordem Chroococcales, três Nostocales e 22 Oscillatoriales. No segundo capítulo foram investigados os fatores que podem estar envolvidos na determinação da presença e/ou ausência de cianobactérias dentro da comunidade das esteiras microbianas em cada lago amostrado. Os lagos das regiões Ross Island, McMurdo Ice Shelf e Upper e Lower Wright Vallyes apresentaram algumas características específicas próprias de cada área em termos de fatores físico-químicos e diversidade de cianobactérias, embora em vários casos houve uma sobreposição considerável das características. A análise multivariada dos dados, com base em variáveis físico-químicas mostrou que os lagos de cada área amostrada tendeu a se agruparem por local, embora com considerável sobreposição, com os dois Wright Valleys e as duas zonas costeiras tendendo a ser mais semelhantes entre si. Este padrão tendeu a ser reproduzido em análises dos dados de biomassa e composição das espécies, onde foi possível indentificar táxons que foram amplamente espalhados por toda a região e outros que foram mais restritos por área. A importância da dispersão e condições de crescimento na condução desse padrão foi discutida. No terceiro capítulo foi desenvolvido um experimento para avaliar o papel de cepas de cianobactérias isoladas no processo de formação de esteiras microbianas. Seis cepas de cianobactérias foram utilizadas, em combinações variadas, para formar biofilmes em condições de laboratório: CYN-50 (Phormidium cf. autumnale); CYN-68 (Leptolyngbya A); CYN-65 (Leptolyngbya B); CYN-66 (Microcoleus sp.); CYN-67 (cf. Aphanocapsa) e CYN- 72 (Nostoc sp.). O conteúdo de clorofila-a, exopolissacarídeo e matéria orgânica foi avaliado e utilizado como medida de avaliação do desenvolvimento dos biofilmes. No final do experimento, observou-se que os biofilmes desenvolvidos mostraram-se diferentes em termos de sua morfologia e que as cianobactérias filamentosas “oscilatoriales” são requeridas para a formação de biofilme consistente, entretanto, todas as cepas morfologicamente diferentes produziram efeito nas matrizes dos biofilmes. Phormidium produziu o melhor biofilme desenvolvido. Em conclusão, este trabalho fornece um maior conhecimento sobre a taxonomia e ecologia de cianobactérias da Antártica na região do McMurdo Sound. Nós identificamos uma mistura de organismos amplamente distribuídos e tolerantes e outros com distribuições mais locais e requerimentos ambientais específicos. A significância destes em temos de gestão da biodiversidade antártica também foi discutida. *INGLÊS* SANTOS, Claudineia Lizieri dos, D.Sc., Universidade Federal de Viçosa, March of 2014. Environmental attributes in assembling cyanobacterial communities from the Mcmurdo Sound region, Antarctica.
The variety of microbial ecosystems that exist in Antarctica represents an extraordinary opportunity for research on microbial ecology, diversity and evolution, particularly in terms of cyanobacteria. In this work we focus on the role of environment in controlling cyanobacterial mat assembly, and begin by describing the cyanobacterial diversity of mats along environmental gradients in the McMurdo Sound region, continental Antarctica. We then evaluated the role of environmental variables in determining their composition by analysing water and microbial cyanobacterial mat samples from 25 ponds from four distinct geographic sites: McMurdo Ice Shelf, Ross Island and Upper and Lower Wright Valleys. Finally we undertook a series of laboratory experiments to determine the extent to which species composition affects mat formation. Twenty nine morphospecies are identified and described in chapter one. Four were assigned to the order Chroococcales, three to the Nostocales and 22 to the Oscillatoriales. In chapter two, we investigated the factors that appeared to determine the presence or absence of morphospecies within the cyanobacterial mat community at each sampled pond. Ross Island, McMurdo Ice Shelf and Upper and Lower Wright Valleys ponds each showed some specific features in terms of physical-chemical factors and cyanobacteria diversity, though in many cases there was considerable overlap. Multivariate analysis based on physic-chemical variables showed that the ponds from each site tended to cluster by site, though with considerable overlap, and with the two Wright Valley and two coastal sites tending to be more similar to each other. This pattern tended to be reproduced in analysis of biomass and species composition data, and we were able to identify taxa that were broadly spread across the region and others that were more restricted by area. The importance of dispersal and growth conditions in driving this pattern is discussed. In chapter 3 we developed an experiment to evaluate the role of isolated cyanobacteria strains on the mat-building process. Six cyanobacteria strains, in varying combinations, were used to grow mats under laboratory conditions: CYN-50 (Phormidium cf. autumnale); CYN-68 (Leptolyngbya A); CYN-65 (Leptolyngbya B); CYN-66 (Microcoleus sp.); CYN-67 (cf. Aphanocapsa) and CYN-72 (Nostoc sp.). The content of chlorophyll-a, exopolysaccharide and organic matter was evaluated to assess mat development. At the end of our experiment, we observed that the mats developments showed variety in terms of their morphology, that oscillatorean cyanobacteria are required for coherent mat formation, but that different strains all produced effect mat matrices. P. autumnale produced the best developed mats. In conclusion, our findings provide an increased knowledge on the Antarctica cyanobacteria taxonomy and ecology in the McMurdo Sound region. We identified a mix of broadly tolerant, widely distributed organisms and other with more local distributions and specific environmental requirements. The significance of this in terms of management of Antarctic biodiversity is discussed.

During the Austral Spring of 2007-2008 the ANtarctic geological DRILLing program (ANDRILL) recovered a 1,138 meter long sediment core AND-2A from the western side of the Victoria Land Basin for the Southern McMurdo Sound Project. The main goal of the project is to help establish a Neogene (~24 to 1.6 Mya) ice volume and climate record of Antarctica. This study focuses on the foraminifera record of AND-2A for paleoenvironmental and biostratigraphic purposes.AND-2A is unique in that it contains a Middle Miocene record (~17 to ~11 Mya) that includes the Middle Miocene transition of warm climatic conditions favoring polythermal ice sheets to major cooling into polar conditions resulting in the quasi-permanent formation of the East Antarctic Ice Sheet. This Middle Miocene transition has not been previously recovered from the Antarctic continental margin.The foraminifer record is not abundant; however, three assemblage zones are identified throughout AND-2A. Calcareous benthic taxa dominate every assemblage, as well as displaying similarities between modern shallow shelf assemblages around Antarctica and assemblages from previous drilling projects in the Ross Sea sector. The foraminifera record displays a dynamic environmental record and is supported by both the sedimentologic and other paleontologic findings.

Phocid seals (true seals, Order Carnivora, Family Phocidae) use a diverse array of breeding habitats and strategies, and produce many vocalizations. Therefore, phocids are well suited as subjects for study of reproductive strategies and the role of vocalizations in species mating at sea. However, the amount of information is still limited for aquatically breeding pinnipeds. Using underwater audio and video recordings of Weddell seals (Leptonychotes weddellii) interacting in McMurdo Sound, I compared the frequencies of vocalizations and behaviors of males and females during the mating season. I also investigated differences in these frequencies based on the social context. Finally, I identified patterns of vocalizations and behaviors to help determine the behavioral context of calls and used this information as a basis for considering the degree of ritualization in Weddell seal displays. Mews, growls, knocks, and trills were found to be almost exclusively male-specific. The territorial male produced chirps more often when another male was present in its territory; whereas, mews and growls were more frequent when one or more free-ranging females were present. Several vocal and behavioral padeparture of the territorial male into or from the breathing hole. In the context of an evolutionary-based model of communication, these findings suggest that low-frequency vocalizations and stereotyped displays produced by territorial males may have been favored by sexual selection: they may provide reliable information to females about the fitness of the signaler and influence their choice of mate. They may also help in limiting conflicts between the territorial male and females over access to the breathing hole.

The aim of this research was to demonstrate the relationship between variations in summertime surface mass balance of the McMurdo Ice Shelf and atmospheric processes. The approach encompassed a broad range of techniques. An existing energy balance mass balance model was adapted to deal with debris-covered ice surfaces and modified to produce distributed output. Point based surface energy and mass balance for two key surfaces of the ice shelf were linked to different synoptic types that were identified using a manual synoptic classification. The distributed model was initialised with distributed parameters derived from satellite remote sensing and forced with data from a regional climate model. Patterns of summertime surface mass balance produced by the distributed model were assessed against stake measurements and with respect to atmospheric processes. During the summers of 2003-2004 and 2004-2005 an automatic weather station (AWS) was operated on bare and debris-covered ice surfaces of the McMurdo Ice shelf, Antarctica. Surface mass balance was calculated using the energy balance model driven by the data from the AWS and additional data from permanent climate stations. Net mass balance for the measurement period was reproduced reasonably well when validated against directly measured turbulent fluxes, stake measurements, and continuously measured surface height at the AWS. For the bare ice surface net radiation provided the major energy input for ablation, whereas sensible heat flux was a second heat source. Ablation was by both melt (70%) and sublimation (30%). At the debris-covered ice site investigated, it is inferred that the debris cover is sufficient to insulate the underlying ice from ablation. Synoptic weather situations were analysed based on AVHRR composite images and surface pressure charts. Three distinct synoptic situations were found to occur during the summers, these were defined as Type A, low pressure system residing in the Ross Sea Embayment; Type B, anticyclonic conditions across region; and Type C, a trough of low pressure extending into the Ross Sea Embayment. A dependence of surface energy fluxes and mass balance on synoptic situation was identified for the bare ice surface. The distributed model was found to produce spatial patterns of mass balance which compared well with stake measurements. Mass balance patterns show that the McMurdo Ice Shelf was generally ablating in the west, and accumulating in the east during summer. Areas of enhanced ablation were found which were likely to be caused by the surface conditions and topographic effects on the wind field. The mean summertime surface mass balance across the entire ice shelf for the 2003-2004 and 2004-2005 summers were –2.5 mm w.e. and –6.7 mm w.e. respectively. The differences between the two summers are inferred to be a result of more frequent type A conditions occurring during the summer of 2004-2005.

The aim of this study is to characterise the structure of refrozen cracks, and to deduce the details of their formation. Surveys and experiments are conducted on straight-sided, linear, refrozen cracks of width 80 mm to 340 mm in land-fast first-year sea ice in McMurdo Sound, Antarctica. Refreezing of cracks is simulated analytically, and with a numerical fluid dynamics model of brine movement in the porous sea ice and in the ocean. Systematic arch-shaped patterns of inclusions, upstream-growing crystals, and two-dimensional variations in salinity are identified in completely and partially refrozen, natural cracks, and in artificial cracks. Using a two-dimensional thermistor array, a relationship between the development of the sea ice structure and the temperature records is found, which identifies the transition from the porous, skeletal layer to consolidated ice in artificial cracks. A two-dimensional analytical model is developed that predicts the measured thickness of consolidated ice in refreezing cracks for this study and for the studies of others. From a heat balance within the refreezing cracks, it is concluded that some of the experiments were conducted in the presence of a negative ocean heat flux. A two-dimensional thermistor array beneath the ice-water interface of a refreezing crack provides evidence for sporadic, cold temperature, advective events at night. A two-dimensional, numerical fluid dynamics model based on the finite volume method is developed to simulate desalination and fluid flow in refreezing cracks. This requires a permeability-porosity relationship for sea ice, which is deduced from data of other groups, combined with the numerical model. To make comparisons among data sets, an analytical approximation is derived for the relationship between connected pore space and total pore space of a random porous medium, based on a Monte Carlo model that is adapted to the crystal structure of sea ice. The permeability-porosity relationship derived in this study is in good agreement with permeability functions published recently. The refreezing of cracks simulated with the numerical fluid dynamics model is consistent with experiments and with the analytical model. In addition, the numerical model simulates the high porosity, arch-shaped freezing front and inclusion structure. Supercooling of the liquid is found to cause excessive heat loss in the simulation. Since a large oceanic heat flux was not observed in the experimental heat balance of refreezing slots, it is suggested that this indicates platelet ice formation or frazil ice formation at the vertical crack interface in Antarctic experiments.

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.

Detailed information on diet and foraging behavior is necessary for understanding predator-prey interactions and food-web dynamics. The primary objective of this dissertation was to gain a more complete understanding of the natural foraging behavior of Weddell seals (Leptonychotes weddellii) in McMurdo Sound, Antarctica using a video data recorder to document the seal's three-dimensional movements and encounters with prey. Seals exhibited a variety of dive types that could be sorted into five groups based on 18 dive descriptors. Three of these groups (deep aerobic, deep anaerobic, and shallow aerobic) were identified as foraging dives, the frequency of which varied with bathymetry. Deep aerobic foraging dives were similar in depth and duration to foraging dives in previous studies and were more common at offshore breathing holes. However, differences occurred between offshore free-ranging and isolated-hole dives in the behaviors involving descent and the frequency of certain behavioral transitions. These differences were responses by the seals to variations in prey abundance, rather than responses to a change in breathing hole availability. Even with an apparently homogenous sample of seals, there was significant individual variability in foraging success, behavior, diet, and foraging tactics. Dive depth, duration, distance, and energetic cost were important for explaining foraging success when seals dove in shallow areas where Antarctic silverfish (Pleuragramma antarcticum) were more difficult to reach and less abundant. However, the relationship between those variables was not the same for all individuals. Diet and foraging tactics also varied significantly among individuals diving near the coastline. Two coastal seals specialized on silverfish, while two others consumed silverfish and benthic prey. Although benthic prey were more accessible along the coastline than offshore, silverfish, which have a high lipid content, required less handling to consume. Thus, it may be energy-efficient for seals to specialize on silverfish at coastal locations despite the additional time and energy required to travel to depths where silverfish are located. These results helped us understand variability within Weddell seal populations and the basis upon which foraging decisions are made in response to changes in bathymetry, access to breathing holes, and prey abundance and availability.

Thesis (Ph.D.)--University of Nebraska-Lincoln, 2009.
Title from title screen (site viewed July 21, 2009). PDF text: xi, 160 p. : ill. (some col.), col. maps ; 5.84 Mb. UMI publication number: AAT 3350458. Includes bibliographical references. Also available in microfilm and microfiche formats.

Piston core, drill core, and high resolution seismic data from McMurdo Sound were analyzed and tied to litho- and seismic stratigraphic events in the Ross Sea. The data show that the first extensive ice sheet grounding event occurred in the Ross Sea as early as late Oligocene time. Development of the East Antarctic ice sheet, and Oligocene ice sheet grounding may have been triggered by the opening of a seaway between Antarctica and Australia during late Cretaceous/early Paleogene time. As the seaway formed, moist air was advected over the cold Antarctic continental landmass. This led to increased precipitation on Antarctica and to the development of an Antarctic ice sheet by at least late Eocene time. Marine-based ice sheets appear to have waxed and waned on the Ross sea continental shelf since the Oligocene grounding event. These waxing and waning events are thought to be responsible for the development of a global Neogene stratigraphic signature. Stratigraphic analysis of seismic and drill core data from the Ross Sea suggests that the stratal geometry and thickness of glacial marine deposits is strongly controlled by the rate of glacial waxing and waning and the availability of accommodation space which in this instance is largely controlled by basin subsidence. Thick offlapping sequences form when the accommodation is high and glacial fluctuation rates are low, and thin flat-lying sequences are deposited when accommodation is low and glacial fluctuation rates are high. A new statistical technique was devised in order to analyze the complex facies relationships that are found in the stratigraphy of McMurdo Sound. Generally, these analyses show that infilling of the basin has been asymmetric. Volcaniclastic debris dominates the eastern portion of the Sound, while deposition of biogenic, ice-rafted and eolian transported debris, and basal till (during glacial maxima) infills the western Sound and central basin. During temperate interglacial events, meltwater transported debris may play an important role in infilling the Sound. Sedimentation on the volcaniclastic apron of the eastern slope of McMurdo Sound is dissimilar to most submarine fans. It is characterized by a reversal in the distribution of proximal and distal facies.