©2010 Elsevier, Inc. 1 Chapter 2 Cuffey & Paterson

©2010 Elsevier, Inc. 2 FIGURE 2.1 Figure 2.1: Zones of a glacier. Based on Benson (1961) and Müller (1962).

©2010 Elsevier, Inc. 3 FIGURE 2.2 Figure 2.2: (a) The dry-snow zone in Greenland (shown as white) in two years, inferred from microwave reflections. (b) Variations of melt area, compared to variations of summer temperature averaged for coastal stations. The melt area is the area of ice sheet outside the dry-snow zone (the gray regions in panel (a)). Melt area in panel (b) was inferred from microwave emissions, and probably underestimates the true extent. Panel (a) adapted from Steffen et al. (2004). Panel (b) adapted from Abdalati and Steffen (2001) and used with permission from the American Geophysical Union, Journal of Geophysical Research.

©2010 Elsevier, Inc. 4 FIGURE 2.3 Figure 2.3: Variation of density with depth in a temperate glacier in the Yukon (Upper Seward), in West Antarctica (Byrd), and in East Antarctica (Vostok). Upper Seward data are from Sharp (1951). Byrd data are recalculated from Maeno and Ebinuma (1983). Vostok data are those of T. Sowers (Spencer et al. 2001, and pers. comm.). Some smoothing has been applied to the data; examples of point measurements can be seen in Figures 2.4 and 2.5.

©2010 Elsevier, Inc. 5 FIGURE 2.4 Figure 2.4: Increase of density with pressure of the overlying firn at two Antarctic stations. Adapted from Maeno and Ebinuma (1983).

©2010 Elsevier, Inc. 6 FIGURE 2.5 Figure 2.5: Increase of density with depth at Siple Dome, Antarctica (the circles: Hawley et al. 2004), compared to simple model (the heavy solid curve: Equation 2.4). Dashed and dotted lines show how the modelled density changes if accumulation rate is increased by a multiple of 5, or temperature is decreased by 20 °C. Thin solid curve (close to data points) shows the Herron-Langway relation for T = −25.4 °C, ˙ (w. eq.), and initial ρ = 350 kg m−3; curve courtesy of J. Severinghaus.

©2010 Elsevier, Inc. 7 FIGURE 2.6 Figure 2.6: Inferred variation of effective gas diffusivity in polar firn as a function of density, at four locations in East Antarctica (DC = Dome C, V = Vostok, Q = Queen Maud Land, De = site DE08) and one site in arctic Canada (DI = Devon Island). Dome C and Vostok are the coldest sites, and Devon Island the warmest. Diffusivities are low at Devon Island because of ice layers, formed by refreezing of melt. The effective diffusivity, shown here, includes the effects of convective mixing in addition to molecular diffusion; this explains the high surface values at Dome C and Vostok. Diffusivities are normalized to the standard free-air value D0. Adapted from Fabre et al. (2000).