The Integrated Sea Ice Dynamic Experiement (SIDEx)
Abstract
Changes in the Arctic sea ice are enabling increased activity in the Arctic Ocean, demanding improved forecasting of sea ice conditions. Gaps in our fundamental understanding of sea ice mechanical and dynamic processes are limiting our ability to develop operationally useful sea ice forecasts. These knowledge gaps arise partly from past difficulties measuring stress and strain at meter to kilometer scales across a realistic, heterogeneous ice cover. Recent advances in satellite remote sensing, high-precision GNSS, and terrestrial surveying will allow us to make such measurements, closing knowledge gaps, and contributing to improved ice forecasting capacity. The critical knowledge gaps we identify all relate to how stress propagates through a heterogeneous ice cover. We hypothesize that heterogeneity in ice strength controls stress propagation through natural sea ice, creating stress concentrations that govern ice failure locations. If this is true, a model initialized with a realistic ice type and strength parameterization map and forced with known wind and ocean currents could skillfully predict locations of failure at the resolution of the ice map. Ice strength and deformation predictions, therefore, depend on understanding the nature of the stress concentrators embedded in the ice pack and their interactions with stress transmission. We target four processes governing strength heterogeneities and interaction of stress with these at increasing scales: (1) generation of flaws in otherwise coherent ice by thermal tensile cracking; (2) buildup of dynamic stresses on thermal cracks, leading to mechanical fracture; (3) transfer of stress between floes during kinematic interactions (shear, ridging); and (4) propagation of stress across a heterogeneous multi-floe ice cover. We will observe these target processes and test our hypothesis by conducting field programs that collect a dataset over scales between 0.001-10 km capturing (1) ice stress, (2) elastic or creep strains, (3) the location and size of thermal and mechanical fractures, (4) larger dynamic strains, and (5) the morphology of the ice. Field observations will be collected in two smaller efforts and an integrated flagship experiment. The two smaller efforts will target thermal expansion coefficients, stresses, and thermal cracking in isolated landfast ice, as well as test new techniques for observing stress, strain, and fracture in drifting ice. A flagship program in the Beaufort Sea will collect integrated stress, strain, and deformation observations targeting fracture initiation, ridging, multi-floe stress transfer, and deformation scaling processes in drifting pack ice. Knowledge synthesis will be based on an analysis strategy that rigorously combines physical models with data to produce continuous state fields (e.g., stress, strain, temperature) from spatially and temporally incomplete observations. Extracting these fields will be carried out as a Bayesian inverse problem, probabilistically combining physical models, prior knowledge of model parameters, and observational data. Continuous stress-strain fields before, during, and after failure events, will be used to test theories of fracture initiation and predictability of stress transmission at floe-floe interaction scales based on observable ice morphology. Testing models of deformation against our well synthesized stress, strain, fracture, and ice morphology fields will enable key model validations.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 20, 2019
- Source ID
- N000141912605
Entities
People
- Pedro Elosegui
Organizations
- Massachusetts Institute of Technology
- Office of Naval Research
- United States Navy