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Snow / Ice / Climate I Energy and Mass n n “The Essence of Snow / Ice / Climate I Energy and Mass n n “The Essence of Glaciology” Processes of: accumulation – precipitation n ablation – melt, sublimation, calving n n n Transformation of snow firn ice n n wind & avalanche can affect either takes time – depends on mass, temperature, etc Balance of acc & abl energy budget

Energy and Mass n n The annual energy budget of a glacier is the Energy and Mass n n The annual energy budget of a glacier is the sum of inputs minus the sum of outputs ± changes in storage. The annual mass budget of a glacier is the specific (at-a-point) budget times the area to which it applies, summed across the entire glacier: n Bn = Σ(1 -i) (bni x Ai)

Energy Budget n INPUTS n Solar (short-wave) radiation n Long-wave radiation n Conduction (air) Energy Budget n INPUTS n Solar (short-wave) radiation n Long-wave radiation n Conduction (air) n Conduction (ground) n Convection (air) [sensible] n Latent heat n Condensation, freezing n OUTPUTS Reflection [albedo] Long-wave Conduction Convection Latent heat Evaporation, melt ? ? energy from sliding/friction, water flow ?

Energy Balance? n n Varies with position on a glacier, time of day, season, Energy Balance? n n Varies with position on a glacier, time of day, season, cloud cover, wind … Convection often estimated by difference (assuming balance) “Balance” implies no change in storage (temperature) Studies are rare because of difficulty.

Examples of Energy Budgets Examples of Energy Budgets

Specific Mass Budget – Stratigraphic n n Most commonly, End Of Summer to EOS Specific Mass Budget – Stratigraphic n n Most commonly, End Of Summer to EOS Uses old snow / firn / ice as a marker

Specific Mass Budget Protocols n n Stakes = aluminum conduit melted into ice Winter Specific Mass Budget Protocols n n Stakes = aluminum conduit melted into ice Winter balance (bw) n n Summer balance (b. S) n n bw = depth of snow x density (= “water equivalent”) bs = bn – bw (accumulation area) bs = bw + lost ice times 0. 917 (ablation area) Firn line, bn = 0 Equilibrium line altitude (ELA), bn = 0

Specific Mass Budget Trends n n n Accumulation often increases slightly with increasing altitude Specific Mass Budget Trends n n n Accumulation often increases slightly with increasing altitude above the ELA. @ ELA, bn = 0 Ablation increases rapidly with decreasing altitude below the ELA.

Specific Mass Budget with Climate n n n “Accumulation gradient” = Δmassacc/Δelevation = mm. Specific Mass Budget with Climate n n n “Accumulation gradient” = Δmassacc/Δelevation = mm. H 2 O/melevation “Ablation gradient” = Δmassabl /Δelevation = mm. H 2 O/melevation “Activity gradient” = gradient @ ELA Maritime = high activity gradient Continental = low A. G.

Specific Mass Budget with Climate n n n “Accumulation gradient” = Δmassacc/Δelevation = mm. Specific Mass Budget with Climate n n n “Accumulation gradient” = Δmassacc/Δelevation = mm. H 2 O/melevation “Ablation gradient” = Δmassabl /Δelevation = mm. H 2 O/melevation “Activity gradient” = gradient @ ELA Maritime = high activity gradient Continental = low A. G.

Why is the ablation gradient >> the accumulation gradient? n n Accumulation = f Why is the ablation gradient >> the accumulation gradient? n n Accumulation = f (precip) Ablation = f (melt) n n Melt = f (T, albedo) n snow ~ 0. 9 n ice ~0. 5 n debris ~ 0. 2, BUT can also insulate other reasons?

Specific Mass Budget with Time n n n Remarkably consistent! Shape = f (climate) Specific Mass Budget with Time n n n Remarkably consistent! Shape = f (climate) Position = f (weather)

Snow / Ice / Climate II Snowlines – Space and Time n Snowlines and Snow / Ice / Climate II Snowlines – Space and Time n Snowlines and their many definitions n n Estimating bn = 0 Contemporary controls on snowlines n local climate / weather and topography Spatial variability n Temporal variability n Pleistocene snowlines and climates n

Snowlines I – Cirque Floors n n Permanent snowfields? No – glaciers! Cirque floor Snowlines I – Cirque Floors n n Permanent snowfields? No – glaciers! Cirque floor elevations Maximum erosion at minimum size n Problems = size, timing n

Snowlines II – Lateral Moraines n Highest laterals = initiation of deposition [discuss more Snowlines II – Lateral Moraines n Highest laterals = initiation of deposition [discuss more with “glacier flow” ? ] n Problem = postglacial slope erosion/removal

Snowlines III – Glaciation Threshold n n True “snowline” Problems = many Area? n Snowlines III – Glaciation Threshold n n True “snowline” Problems = many Area? n Topography? n Summits > glacier elevations n

Snowlines IV – THAR n n n Toe-headwall altitude ratio Requires reconstruction Assumes known Snowlines IV – THAR n n n Toe-headwall altitude ratio Requires reconstruction Assumes known “correct” ratio – 40%?

Snowlines V – AAR n Accumulation area ratio n Requires complete reconstruction n Assumes Snowlines V – AAR n Accumulation area ratio n Requires complete reconstruction n Assumes correct ratio. 55–. 60–. 65 ? n [topo map method]

Snowline Comparisons n Meierding (1982) CO Front Range n tried many ratios n n Snowline Comparisons n Meierding (1982) CO Front Range n tried many ratios n n Locke (1990) Montana n small glaciers n s. d. ~ 350 m n CF (n=12) LM (45) GT (13) THAR (24) AAR (24) 3161 m 3188 3388 3161 (40%) 3163 (65%) CF (n=400) 2347 m LM (321) 2121 THAR (330) 2355 (40%) AAR (264) 2353 (65%)

ELA = representative? n Many studies say so! n e. g. , Sutherland (1984) ELA = representative? n Many studies say so! n e. g. , Sutherland (1984) n ELA balance represents average winter balance for entire glacier n Measure once – use a lot!

Glacial Climates n Glaciers exist only in a narrow range of climates = f(winter Glacial Climates n Glaciers exist only in a narrow range of climates = f(winter ppt and summer T) n = f(P, T, and continentality n

Glacial Climates Glacial Climates

Controls on Snowlines I – Latitude n Latitude ≈ temperature (treeline) n n Latitude Controls on Snowlines I – Latitude n Latitude ≈ temperature (treeline) n n Latitude ≠ precipitation (snowlines) n n highest near equator saddle near equator Weak gradients (<1 m/km)

Controls II – Continentality n n n Lowest near moisture source Higher inland Strong Controls II – Continentality n n n Lowest near moisture source Higher inland Strong gradients n up to 10 m/km

No Hem Glaciers n n n Latitude? Continentality Ocean currents n Local precipitation No Hem Glaciers n n n Latitude? Continentality Ocean currents n Local precipitation

Temporal Resolution n Glaciers respond at annual to decadal scales Temporal Resolution n Glaciers respond at annual to decadal scales

Temporal Inconsistency n n Not all glaciers respond similarly Not even glaciers in the Temporal Inconsistency n n Not all glaciers respond similarly Not even glaciers in the same region!

Temporal Inconsistency n n Not all glaciers respond similarly Not even glaciers in the Temporal Inconsistency n n Not all glaciers respond similarly Not even glaciers in the same region!

Wahrhaftig and Birman, 1965 n Sierra Nevada n Note effects of subtropical high & Wahrhaftig and Birman, 1965 n Sierra Nevada n Note effects of subtropical high & rain shadow Pleistocene Snowlines I

Pleistocene Snowlines II n n US West (Porter et al. 1983) Effects of: Sub. Pleistocene Snowlines II n n US West (Porter et al. 1983) Effects of: Sub. T High n Westerlies n Storm tracks n Orography n

Pleistocene Snowlines II Pleistocene Snowlines II

Montana Climate & Glaciers n n Glaciers Inferred air mass movement Residuals Inferred causes Montana Climate & Glaciers n n Glaciers Inferred air mass movement Residuals Inferred causes

MT/ID Paleoclimate n n Complex pattern! More detailed than modern weather stations and SNOTEL MT/ID Paleoclimate n n Complex pattern! More detailed than modern weather stations and SNOTEL sites!

Spatial Resolution n n Humlum (1985) West Greenland Local data are consistent Needs no Spatial Resolution n n Humlum (1985) West Greenland Local data are consistent Needs no smoothing High resolution!