Sea ice strain, stress, and fracture activity at kilometer scales

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Author
Fedders, Emily R.
Chair
Mahoney, Andrew R.
Committee
Hutchings, Jennifer K.
Meyer, Franz
Polashenski, Chris
Richter-Menge, Jacqueline
Keyword
Sea ice drift
Chukchi Sea
Beaufort Sea
Arctic Ocean
Mathematical models
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URI
http://hdl.handle.net/11122/15965
Abstract
Through-thickness fractures including cracks, leads, and pressure ridges divide sea ice into individual plates and plate assemblies. While they remain intact, plates deform via continuous strain as they interact. Radar interferometry can identify active fractures at plate assembly boundaries and measure the continuous strains between them at high spatial resolution and spatial scales from meters to kilometers. However, interferograms are only sensitive to the one­ dimensional component of surface strain parallel to a radar’s lines of sight. Working with coauthors, I develop a novel analytical inverse model to estimate two-dimensional, horizontal surface motion from the one-dimensional information provided by interferograms over areas of ice experiencing spatially uniform strain. Model results accurately capture thermal strain in sheltered landfast ice and realistically estimate rigid displacements in drifting ice. In areas of non-uniform strain, we combine one-dimensional interferometric strain measurements with field observations from a sea ice camp in the Beaufort Sea to investigate relationships between strain, stress, and fracture activity. We calculate the first published estimates of the effective elastic modulus, E*, and effective Poisson’s ratio, v*, of in situ drifting sea ice under natural loading rates. We estimate E* within the range typically used in sea ice models but estimate v> > 0.5, larger than typically assumed and indicative of anisotropy in sea ice Poisson response at low strain rates. Finally, we synthesize interferometric records of strain and fracture to identify an approximately 1 km radius of influence of impact forces resulting from contact across active fractures. We also identify apparent fracture reactivation after multi-day quiescent periods, indicating prior fractures may remain weaker than surrounding ice for such periods. Together, this work outlines both new observations and new tools for future researchers to utilize in studies of sea ice mechanics and dynamics at intermediate scales in areas of high-concentration winter pack ice.
Description
Dissertation (Ph.D.) University of Alaska Fairbanks, 2025
Table of Contents
Chapter 1: General introduction -- 1.1 Observing sea ice strain and deformation at meter to kilometer scales -- 1.2 References. Chapter 2: Two-dimensional thermal and dynamical strain in landfast sea ice from InSAR: results from a new analytical inverse method and field observations -- 2.1 Abstract -- 2.2 Introduction -- 2.3 Study sites -- 2.3.1 Elson lagoon -- 2.3.2 Chukchi Sea near Utqiagvik, Alaska -- 2.4 Datasets -- 2.4.1 12-day Sentinel-1 interferograms over Elson Lagoon -- 2.4.2 10-second TanDEM-X interferograms over the Chukchi Sea -- 2.4.3 Laser strain observatory measurements of surface displacement in Elson Lagoon -- 2.5 Principles of InSAR for sea ice monitoring -- 2.5.1 Contributions to interferometric phase -- 2.5.2 Excluding non-deformation components of phase -- 2.5.3 Identification and exclusion of vertically-dominated displacement -- 2.6 Phase unwrapping over regions of smoothly varying phase (RSVPs) -- 2.6.1 RSVP identification -- 2.6.2 Phase unwrapping within RSVPs in Sentinel 1 interferograms -- 2.6.3 Phase unwrapping within RSVPs in TDX interferograms -- 2.7 Modeling 2D horizontal sea ice displacement and strain from single orbit InSAR -- 2.7.1 Analytical inverse method for radially symmetric modes -- 2.7.2 Analytical inverse method for axially symmetric modes -- 2.7.3 Analytical inverse method for translation -- 2.7.4 Strain calculation from modeled horizontal displacements -- 2.7.5 Addressing model ambiguity in Elson Lagoon -- 2.7.6 Addressing model ambiguity in the Chukchi Sea -- 2.8 Results -- 2.8.1 Single-mode modeled displacement and strain in landlocked ice from InSAR -- 2.8.2 Displacement and strain in landlocked ice from point observations -- 2.8.3 Comparison between observed and modeled displacements on Elson Lagoon -- 2.8.4 Two-mode modeled strain and displacement in drifting pack ice -- 2.9 Discussion -- 2.9.1 Implications of strain results -- 2.9.2 Physical interpretation of RSVPs -- 2.10 Conclusions -- 2.11 Acknowledgements -- 2.12 References. Chapter 3: Effective elastic parameters for in situ, drifting sea ice under natural forcing at kilometer scales -- 3.1 Abstract -- 3.2 Plain language summary -- 3.3 Introduction -- 3.4 Data collection and processing -- 3.4.1 The Sea Ice Dynamics Experiments (SIDEx) drifting ice camp -- 3.4.2 Ground-based radar image acquisition and interferogram calculation -- 3.4.3 Identification of continuous regions of smoothly varying phase (RSVPs) -- 3.4.4 Calculating change in look-parallel, horizontal strain -- 3.4.5 Additional quality control measures for ∆ε|| -- 3.5.6 In-ice stress measurements -- 3.4.7 Ice type observations -- 3.5 Results -- 3.5.1 Overview of observed strain changes -- 3.5.2 Variation in rate of strain change with ice type -- 3.5.3 Overview of observed stress changes -- 3.5.4 Variation in rate of stress change with ice type -- 3.6 Discussion -- 3.6.1 Stress-strain comparison in an elastic framework -- 3.6.2 Evaluating impacts of ice temperature, thickness, and ice type -- 3.7 Conclusions -- 3.8 Acknowledgements -- 3.9 References. Chapter 4: Reconsidering the floe in consolidated sea ice: fracure pathways and the influence of contact geometry on spatial strain variation at intermediate scales -- 4.1 Abstract -- 4.2 Introduction -- 4.3 Data and methods -- 4.3.1 The Gamme Portable Radar Interferometer (GPRI) -- 4.3.2 Identifying lines of damage (LDs) -- 4.3.3 Identifying regions of smoothly varying phase (RSVPs) -- 4.3.4 Excluding non-horizontal strain influences -- 4.3.5 Calculating one-dimensional strain within the central RSVP -- 4.3.6 Ice classification mapping using field observations and synthetic aperture radar -- 4.4 Results -- 4.4.1 Lines of damage (LDs) -- 4.4.2 Fracture zone activity, quiescence, and re-use -- 4.4.3 Temporal evolution of strain and damage -- 4.5 Discussion -- 4.5.1 Influence of prior damage on present and future fracture pathways -- 4.5.2 RSVP transcience -- 4.5.3 RSVPs are distinct from MYI or FYI floes -- 4.5.4 Prevalence of elevated strain near RSVP edges -- 4.6 Conclusion -- 4.7 Acknowledgements -- 4.8 References. Chapter 5: General conclusions -- 5.1 A detailed look at strain variability and fracture activity -- 5.2 Future opportunities for model-observation synthesis -- 5.3 References.
Date
2025-05
Type
Dissertation
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