No description available.

No description available.

Seasonal sea ice – ice which freezes in late fall and melts completely the following summer – is a central feature in the ecology, geomorphology, and climatology of the Bering Sea. In this region's coastal zones, sea ice becomes locked into a stationary position against the coastlines to become landfast ice, which influences bioegophysical processes in the region, as well as exchanges of energy and matter among land, ocean, and atmosphere. It provides a platform for human mobility and subsistence activities, habitat for certain marine mammals, regulates terregenous nutrient cycling into ocean environments, and modulates the effect of erosive wind/wave action against coastlines. However, a thorough understanding of how this stationary ice, known as landfast ice, affects biogeophysical processes in the Bering Sea is limited by a lack of data on its areal coverage and seasonal duration. This dissertation establishes a baseline set of observations of landfast ice conditions in the Bering Sea through the creation and analysis of continuous spatial datasets. Chapter 1 focuses on the landfast ice annual cycle in the Eastern Bering Sea, which spans from the western tip of the Seward Peninsula to the southernmost point on the Yukon-Kuskokwim River Deltas. Chapter 1 results in the creation of landfast ice spatial data in these areas ranging from 1996 – 2008. Results show the spatial distribution and seasonal duration of landfast ice vary regionally within our study area, does not generally reach water depths associated with stabilization of the landfast ice cover in other regions of the Arctic, and is shortening in seasonal duration by approximately 9 days. Chapter 2 focuses on the landfast ice annual cycle on St. Lawrence Island, an Alaska Island located in the northern Bering Sea. Chapter 2 results in the creation of landfast ice spatial data in these areas ranging from 1996 – 2019. Results show the spatial distribution of landfast ice to vary regionally on the island, based on the coastlines orientation towards prevailing winds that transport pack ice through the Bering Strait. We also observed a sharp decline in landfast ice cover from 2017-2019, which coincides with record-breaking declines in sea ice coverage for the entire Bearing Sea. We also found coastal morphology and orientation have limited explanatory power when modeling landfast ice widths – the distance between the landfast ice edge and coastline – suggesting the consideration of meteorological variables is needed to improve models. Chapter 3 uses the landfast ice data from Chapter 2 to create an explanatory logistic regression model of landfast ice cover on St. Lawrence Island, using a combination of geographic and meteorological predictor variables. Using these variables, the model was able to predict the location of landfast ice cover with 80-90% accuracy, depending on the region of St. Lawrence Island. The model outputs resulted in very low commission error, with high omission error, which may be improved in future studies with the additional predictor variables. Cumulatively, this dissertation is the most comprehensive analysis of landfast ice cover to date on Alaskan Bering Sea coastlines. Research findings advance scholarly understandings of coastal ice conditions in the Bering Sea, and the geographic as wellas meteorological factors that enable their presence. / Doctor of Philosophy / Landfast sea ice – sea ice that becomes locked into a stationary position against the coastline – is a central feature in the ecology, geomorphology, and climatology of the Bering Sea. However, a thorough understanding of how this stationary ice, known as landfast ice, affects human/environmental processes (e.g. climate regulation, sediment mixing in marine environments, wildlife habitat/behavior, human transportation) in the Bering Sea is limited by a lack of data on its areal coverage and seasonal duration. This dissertation establishes a baseline set of observations of landfast ice conditions in the Bering Sea through the creation and analysis of continuous spatial datasets. Cumulatively, this dissertation is the most comprehensive analysis of landfast ice cover to date on Alaskan Bering Sea coastlines. First, this dissertation creates and analyzes the landfast ice annual cycle from 1996 – 2008 on the Eastern Bering Sea. Second, this dissertation creates a similar dataset from 1996 – 2019 on St. Lawrence Island, finding significant declines in landfast ice coverage that match broader sea ice trends in the northern Bering Sea. Third, this dissertation uses the landfast ice data on St. Lawerence Island to create a model explaining outcomes in the location of landfast ice cover under certain geographic and meteorological conditions.

No description available.

The internal structure of ice sheets reflects the history of flow and deformation experienced by the ice mass. Flow and deformation are controlled by processes occurring within the ice mass and at its boundaries, including surface accumulation or ablation, ice rheology, basal topography, basal sliding, and basal melting or freezing. The internal structure and basal environment of ice sheets is studied with ice-penetrating radar. Recently, radar observations in Greenland and Antarctica have imaged large englacial structures rising from near the bed that deform the overlying stratigraphy into anticlines, synclines, and overturned folds. The mechanisms that may produce these structures include basal freeze-on, travelling slippery patches at the ice base, and rheological contrasts within the ice column. In this thesis, I explore the setting and mechanisms that produce large basal stratigraphic structures inside ice sheets. First, I use radar data to map subglacial hydrologic networks that deliver meltwater uphill towards freeze-on structures in East Antarctica. Next, I use a thermomechanical flowline model to demonstrate that trains of alternating slippery and sticky patches can form underneath ice sheets and travel downstream over time. The disturbances to the ice flow field produced by these travelling patches produce stratigraphic folds resembling the observations. I then examine the overturned folds produced by a single travelling sticky patch using a kinematic flowline model. This model is used to interpret stratigraphic measurements in terms of the dynamic properties of basal slip. Finally, I use a simple local one-dimensional model to estimate the thickness of basal freeze-on that can be produced based on the supply of available meltwater, the thermal boundary conditions, ice sheet geometry, and the ice flow regime.

Thesis (M.Eng.)--Memorial University of Newfoundland, 2002. / Bibliography: leaves 115-116.

An ice nucleating protein (INP) with 66% amino acid sequence identity to the better-known INP of Pseudomonas syringae has been described in an environmental isolate of P. borealis and designated InaPb. Despite the fact that INPs are classified as ice-binding proteins, InaPb showed little affinity for pre-formed ice and showed incorporation rates similar to Ina- strains. Additionally, it appeared to lack in the ability to shape ice or limit its growth. However, it was an effective ice nucleator. Using the coding sequence for InaPb and a green fluorescent protein tag (GFP), an InaPb-GFP fusion protein construct was inserted into a broad host expression vector in order to visualize the expression and localization of the protein in E. coli and an Ina- strain of P.syringae. The InaPb-GFP protein appears to localize at the poles of E. coli, but the nucleation temperature for these cells was only marginally above -9°C, which indicated poor nucleation activity. When expressed in Ina- P. syringae, the proteins showed clustering throughout the cell and an increased ability to nucleate ice following cold conditioning. The ability to nucleate ice was further increased by the removal of the GFP tag resulting in an average nucleation temperature more consistent with that seen in the native host P. borealis. Since inaPb transcript levels did not appear to change after cold conditioning, the clustering seen using fluorescence microscopy was likely the result of increased aggregation of protein in the membrane. Most INP- producing bacteria are associated with plant disease, but experiments with P. borealis suggested that the Ina+ phenotype was not indicative of pathogenicity in this strain. It is hoped that my contribution to the functional characterization of this INP will lead to a better understanding of these special proteins and their importance to the handful of bacteria that exhibit this activity. / Thesis (Master, Biology) -- Queen's University, 2012-05-15 09:55:52.506

Antifreeze proteins (AFPs) are produced by a variety of organisms to either protect them from freezing or help them tolerate being frozen. Recent structural work has shown that AFPs bind to ice using ordered surface waters on a particular surface of the protein called the ice-binding site (IBS). These 'anchored clathrate' waters fuse to particular planes of an ice crystal and hence irreversibly bind the AFP to its ligand. An AFP isolated from the perennial ryegrass, Lolium perenne (LpAFP) was previously modelled as a right-handed beta helix with two proposed IBSs. Steric mutagenesis, where small side chains were replaced with larger ones, determined that only one of the putative IBSs was responsible for binding ice. The mutagenesis work also partly validated the fold of the computer-generated model of this AFP. In order to determine the structure of the protein, LpAFP was crystallized and solved to 1.4 Å resolution. The protein folds as an untwisted left-handed beta-helix, of opposite handedness to the model. The IBS identified by mutagenesis is remarkably flat, but less regular than the IBS of most other AFPs. Furthermore, several of the residues constituting the IBS are in multiple conformations. This irregularity may explain why LpAFP causes less thermal hysteresis than many other AFPs. Its imperfect IBS is also argued to be responsible for LpAFP's heightened ice-recrystallization inhibition activity. The structure of LpAFP is the first for a plant AFP and for a protein responsible for providing freeze tolerance rather than freeze resistance. To help understand what constitutes an IBS, a non-ice-binding homologue of type III AFP, sialic acid synthase (SAS), was engineered for ice binding. Point mutations were made to the germinal IBS of SAS to mimic key features seen in type III AFP. The crystal structures of some of the mutant proteins showed that the potential IBS became less charged and flatter as the mutations progressed, and ice affinity was gained. This proof-of-principle study highlights some of the difficulties in AFP engineering. / Thesis (Ph.D, Biochemistry) -- Queen's University, 2012-07-18 15:24:42.082

No description available.

A sea ice model developed by W. D. Hibler (1979) was applied to the Lancaster Sound/Barrow Strait channel in an effort to simulate the observed ice environment. The simulation covered a ten month period, from October 1985 until August 1986. The impact of atmospheric and oceanographic forcing on the development of characteristic ice features that develop seasonally within the channel was examined. The importance of the ice interaction component of the model when simulating a restricted channel ice environment was also examined. The model was able to simulate regional scale processes and conditions within the channel. Small scale localised processes and conditions which control the spatial variability and complexity of the ice regime were not accurately reproduced. Simulation results provided insights into the effect and importance of both the model and geophysical variables examined. The study highlighted concerns that need be addressed in future modelling work in the Lancaster Sound/Barrow Strait channel.