Collaborative Research: Deformation of the Arctic Sea Ice Cover: Formation and Action of Failure Zones

Dartmouth College, Hanover NH

Investigators

Abstract

ABSTRACT Schulson OPP-0328605 Hibler OPP-0328728 The Principal Investigators describe new numerical and laboratory experiments that should elucidates the physical mechanisms that underlie the formation and subsequent behavior of failure zones that form within the annual arctic sea ice cover. The failure zones, termed. linear kinematic features (LKFs), often occur in conjugate sets of sub-parallel faults that traverse a large fraction of the arctic basin. Upon formation, the ice cover generally dilates somewhat and subsequently oscillates, thereby enhancing transfer of heat from the ocean to the atmosphere as well as increasing oceanic salt flux as new ice forms on open water. The LKF.s/faults most probably affect the ice thickness distribution in that, upon subsequent convergence of the ice pack, pressure ridging occurs. The lineaments (and other large-scale fracture features) are similar in appearance to smaller-scale compressive shear faults seen in laboratory specimens, suggesting, when the fractal character of ice breakup is also taken into account, that the physics of fracture is scale independent. Three different sets of numerical experiments will be performed. In the first series, idealized and numerical grid experiments will be carried out to examine the effect of different flow rules on fault formation and on the attendant weakening of the pack. In the second set, idealized spatially-varying wind forcing will be used with heterogeneous initial strength and a laboratory-generated flow rule to investigate the characteristic opening and closing of deformation faults as well as their angle of intersection. In the third series, high-resolution basin-wide modeling will be performed using a full-thickness ice distribution formulation. These simulations will be compared with a variety of recently acquired deformation data, most notably with recently declassified thickness-distribution data from upward-looking submarine sonar observations. Such comparisons will access the utility and applicability of this research to numerical air-ice-ocean models for the numerical investigation of climate. Five sets of systematic biaxial compressive experiments will be performed in the laboratory on blocks of salt-water ice. Intellectual Merit: In focusing on the development of a scale-independent sea-ice model, particularly applicable to spatial resolutions less than 10 kilometers and to the resolution of failure zones/faults, this research represents a new paradigm for sea ice dynamics. Under this paradigm, high internal ice stresses leading to localized fracture occur over short periods of time and rapidly decrease as a fault is formed. This differs significantly from conventional formulations (of the ice pack and its thickness distribution) which are used in current numerical investigations of climate and which implicitly assume a smoothly-varying deformation field in both time and space. The expectation is that the new model will more realistically capture the distribution in sea ice thickness and, thus, will be more useful in the numerical modeling of climate and its sensitivity to the polar sea ice cover. Broader Impacts: The research will constitute an intense intellectual enquiry carried out with the assistance of graduate students at two universities active in polar research. It will contribute to the intellectual development of a new generation of investigators, as well as enhance the research environment of the two institutions. In addition, through the revelation and understanding of new physical effects, the study will enrich both the undergraduate and graduate teaching of the Principal Investigators. The activity will contribute also to a working partnership in polar studies between Dartmouth and The University of Alaska. To enhance scientific and technical understanding, the results of the work will be disseminated broadly, through presentations to workshops and societal meetings and through contributions to the technical and scientific literature. A review article or book chapter is also planned.