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Pressure ridges impact the mass, energy and momentum budgets of the sea-ice cover and present an obstacle to transportation through ice-infested waters. Quantifying ridge characteristics is important for understanding total sea-ice mass and for improving the representation of sea-ice dynamics in high-resolution models. Multi-sensor measurements collected during annual Operation IceBridge (OIB) airborne surveys of the Arctic provide new opportunities to assess the sea ice at the end of winter. We present a new methodology to derive ridge sail height from high-resolution OIB Digital Mapping System (DMS) visible imagery. We assess the efficacy of the methodology by mapping the full sail height distribution along 12 pressure ridges in the western and central Arctic. Comparisons against coincident Airborne Topographic Mapper (ATM) elevation anomalies are used to demonstrate the methodology and evaluate DMS-derived sail heights. Sail heights and elevation anomalies were correlated at 0.81 or above. On average mean and maximum sail height agreed with ATM elevation to within 0.11 and 0.49 m, respectively. Of the ridges mapped, mean sail height ranged from 0.99 to 2.16 m, while maximum sail height ranged from 2.1 to 4.8 m. DMS also delivered higher sampling along ridge crests than coincident ATM data.
This note describes an end-capping procedure used to prepare cylindrical ice-core samples for direct tension testing. The techniques developed build on work done by Cole and others (1985) and Lee (1986), and include a design modification to the loading train and a more reliable approach to establishing the fresh-water bond used to mount the end caps on the sample. Using these techniques, an 88% success rate was achieved in a recent series of uniaxial tension tests.
We present the results of tests done to determine the tensile behavior of first-year columnar sea ice over a range of temperatures from −20° to −3°C and strain rates of 10−5 and 10−3s−1. The temperature of a test specimen was dictated by its in-situ location within the sea-ice sheet; samples located near the top of the sea-ice sheet were tested at the lower temperatures. A tensile load was applied along the cylindrical axes of the test specimens, which were perpendicular to the growth direction of the ice. Results showed that the maximum stress reached during a test was most strongly influenced by temperature, while the failure strain and the modulus were principally affected by the loading rate. A model relating the tensile strength of the ice to its porosity based on temperature-dependent variations in the brine-pocket geometry is evaluated.
In situ measurements of ice stress were made on a multi-year floe in the
Alaskan Beaufort Sea over a 6 month period, beginning in October 1993. The
data suggest that, in this region of the Arctic during this experiment,
there were two main sources of stress: a thermally induced stress caused by
changes in air temperature, and a stress generated by ice motion. Due to the
natural damping of the snow and ice above the sensor, the thermally-induced
stresses are low frequency (order of days). Stresses associated with periods
of ice motion have both a high-frequency (order of hours), and
low-frequency, content. The relative significance of these sources of stress
is seasonal, reflecting the changes in the strength and continuity of the
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