Cloudy band observations for annual layer counting on the GRIP and NGRIP, Greenland, deep ice core samples (scientific note)

Cloudy band stratigraphy was observed in the GRIP and NGRIP, Greenland ice cores. Gray value profiles obtained from the photographic recording were analyzed to extract annual layer signals. Simple counting of gray value peaks is effective enough when annual layer thickness is relatively small (smaller than approximately 20 mm), but smoothing of the gray value profile is needed when annual layer thickness is larger. Smoothing can be done by adopting a running mean over a range of half of annual layer thickness estimated from ice flow modeling. A comparison of the DEP profile with the gray value profile revealed that the DEP profile seems to reflect the seasonal variation in general, but not exactly

Mechanical anisotropy of deep ice core samples by uniaxial compression tests (scientific paper)

Mechanical anisotropy of ice core samples has been observed in various uniaxial compression tests. The c-axis orientation distribution is the primary influence on the mechanical behavior of ice cores. A strong single-maximum fabric pattern is observed in the deep parts of the ice sheet. In this region, polycrystalline ice is very hard along the vertical axis; however, it easily shears along the horizontal plane. Thus, by acquiring the distribution of c-axis orientations throughout the ice sheet, the mechanical anisotropy of ice sheet flow behavior can be understood. Analysis of fabric measurements on the Dye 3, GRIP, and Dome F ice cores suggests that the c-axis orientation distribution depends primarily on vertical strain. Therefore, if the ice thickness at some point in the ice sheet is known, it should be possible to predict the distribution of c-axis orientations at that depth. Uniaxial compression tests were carried out along various directions of the Dye 3, GRIP, and Dome F ice cores. A contour map of mechanical anisotropy was then made to relate the compression direction to the vertical strain. This clarified the flow enhancement factor in every compression direction at a given vertical strain

Comparative studies in method for stratigraphical structure measurement of ice cores: Identification of cloudy bands

Cloudy bands are typical stratigraphic structure in deep ice core. Detailed recording of cloudy bands is important for dating of ice core since pair of series cloudy band and clear layer is corresponds to annual layer and it sometimes corresponds to volcanic ash layer. We developed two type scanners, transmitted light method and laser tomograph method for the stratigraphic study. Measurements were carried out for NGRIP deep ice core, which containing many cloudy bands, using the two type scanners and digital camera. We discussed about the possibility of identification of cloudy bands by each method and about advantage and disadvantage of measurements and their results

Microscopic observations on microtomed surface of ice

Surface hollows appearing after microtome shaving were observed on poly-and single crystal specimens under an optical microscope in a cold room laboratory. Characteristic shell-shaped hollows appeared with their major axis perpendicular to the shaving direction. Fewer hollows appeared at specimen surfaces when the basal plane of the ice crystal was parallel or perpendicular to the specimen surface. The results observed could be easily interpreted if cleavage cracks form parallel or perpendicular to the basal plane near the blade edge during the microtome shaving process

A bipolar comparison of deep ice cores from Antarctica (Dome Fuji) and Greenland (GRIP)

Oxgen isotope ratio and chemistry profiles were compared to find the corresponding interstadials during the Wisconsin Ice Age between the GRIP (Greenland) and Dome Fuji (Antarctica) deep ice core data for the past one hundred and sixty thousand years. Eight interstadials in GRIPδ^<18>O profile were found to correspond to those in Dome Fuji δ^<18>O profile. Eleven interstadials in GRIPδ^<18>O profile were found to correspond to those in Dome Fuji chemistry (calcium, nitrate and sulfate) profile, which is better suited for the purpose of interstadial search than the δ^<18>O profile at Dome Fuji. The Eemian interglacial period at Dome Fuji seems to be much shorter and more stable than that in the GRIP profile. Three major periods having higher contents of calcium, nitrate and sulfate appear at Dome Fuji, ranging (1) between interstadials number 1 and 8, (2) between interstadials number 17 and 19, and (3) before the Eemian, which correspond to relatively cold and stable periods in the GRIP δ^<18>O profile. These findings promise a favorable outcome from more detailed bipolar comparison in the future for an understanding of climatic linkage conditions and the driving forces between northern and southern hemispheres