Several analyses are given for the flexure of a floating polar ice tongue with the general dimensions of several kilometers wide by 200 in in thickness. The lengths considered are from 2 km to in excess of 10 km which is referred to as a long slab. The analyses are made under the separate assumptions that ice behaves as (1) an elastic material, (2) an elastic-plastic material, and (3) a fully plastic material, when reacting to flexure due to changes in sea-level. The elastic analysis shows that hinge-line stresses could become very high of the order of 15 bar) for slab lengths up to about 3·5 km reacting to sea-level changes of the order of ±50 cm. For slab lengths greater than this, the stresses at the hinge, as well as being significantly less than before, become independent of the length of the slab, dependent only on the slab thickness and the amount of deflection of sea-level. In the elastic-plastic analysis, the hinge-line stress cannot exceed a value of about 2 bar. This yield value is reached when sea-level departs about 50 cm from the mean. The fully plastic analysis requires more accurate knowledge of the constants in the flow law and their variation with density, temperature and salinity within the ice. However, the theory may be tested by measuring the diurnal change in strain-rate across the hinge-line zone. The process of calving of large tabular icebergs from such glacier tongues may demand sea-level changes of more than ± 1 m, or bending about more than one axis of the shelf.

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The Little Ice Age was the most extensive Neoglacial glacier advance in the Canadian Rockies. Evidence of earlier, less-extensive Neoglacial glacier advances is based on wood recovered from several glacier forefields. Wood flushed out of Athabasca Glacier (7550-8230 yr B.P., three dates) and Dome Glacier (6120-6380 yr B.P., two dates) indicates that forests occurred upvalley of present glacier termini during the Hypsithermal. Detrital logs from Peyto (14 dates), Saskatchewan (3 dates), Robson (3 dates), and Yoho (1 date) Glaciers, plus in situ slumps at Peyto and Robson Glaciers, have yielded 14 C dates between 2490 and 3300 yr B.P. (12 dates between 2800 and 2990). This wood is derived from sources at or upvalley from present glacier termini and represents forests overridden by glaciers between ca. 3100 and 2500 yr B.P. (Treeline was higher than present immediately prior to this advance.) This advance, which did not extend beyond the Little Ice Age maximum position, is designated the Peyto Advance and correlated with the Tiedemann Advance in western British Columbia. Earliest Little Ice Age advances at Peyto and Robson Glaciers are dated ca. 800-600 yr B.P. at positions ca. 500 m upvalley from Little Ice Age limits.

Dark marks in the rings of white spruce less than 50 yr old in Yukon, Canada, are correlated with the number of stems browsed by snowshoe hares. The frequency of these marks is positively correlated with the density of hares in the same region. The frequency of marks in trees germinating between 1751 and 1983 is positively correlated with the hare fur records of the Hudson Bay Company. Both tree marks and hare numbers are correlated with sunspot numbers, and there is a 10-yr periodicity in the correlograms. Phase analysis shows that tree marks and sunspot numbers have periods of nearly constant phase difference during the years 1751-1787, 1838-1870, and 1948 to the present, and these periods coincide with those of high sunspot maxima. The nearly constant phase relations between the annual net snow accumulation on Mount Logan and (1) tree mark ratios, (2) hare fur records before about 1895, and (3) sunspot number during periods of high amplitude in the cycles suggest there is a solar cycle-climate-hare population and tree mark link. We suggest four ways of testing this hypothesis.

A vertically stable, step-like thermohaline structure is observed throughout a continuous, 400 m conductivity-temperature-depth (CTD) profile taken near the Erebus Glarer Tongue, McMurdo Sound, Antarctica. The pattern is best developed between the sea surface and 250 m depth, the interval corresponding to that of the irregular underwater profile of the Glacier Tongue. The steps average 17 m in thickness and typically display discontinuities of 0.1 øC in temperature, 0.04 %o in salinity and 3.5 x 10 -4 g cm -3 in density. The observations are compared with theory and laboratory experiments of cell development and lateral flow near ice melting into vertically stratified salt water. At this location, subsurface seawater is inferred to remain above the in situ freezing point year-round, and contains sufficient heat to account for much of the Glacier Tongue thinning by basal melting. An adequate volume of meltwater would result to produce the measured salinity steps. We discuss related observations and some implications of this process for ocean circulation and biological productivity in the Antarctic. identified on nearby station 218, but the relative importance of spatial versus temporal changes could not be determined, as these stations were taken on an opportunity basis. The CTD records are relatively noisy, possibly due to system response time and slow sensor descent rate. The differing descent and ascent profiles, and turbulence near the large local gradients also suggest actively evolving, not remnant features. OCEANOGRAPHIC OBSERVATIONSOn and near the Antarctic continental shelf we have frequently recorded thermohaline staircases of varying dimensions at intermediate depths. Some were of the variety generafly ascribed to double-diffusive processes, e.g., cold fresh over warm salty water beneath the Antarctic Surface Water temperature minimum, or warm salty over cold fresh water below the Circumpolar Deep Water that intrudes onto the continental shelf. At other times, steps were barely discernible, or not much greater than the resolution of the instrumentation then being used. Station 217 is unlike any of the above, but graphically displays a statically stable configuration of relatively warm fresh over cold salty water. This is analogous to the homogeneous summer surface layer that overlies the temperature minimum (steps also occur at that transition), but here the stairs are more uniform and descend to greater depths.The step structure observed here differs in an important respect from that reported, e.g., by Neal et al. [1969], under a drifting ice island in the Arctic. In that case the steps were formed by the one-dimensional process of cooling from Paper number 1C0546.