Lecture 4 core

High arctic climates: low winter temp (-20 - -30) & perpetual darkness. Temp above freezing for 2-3 months of year, surface thaw 0.3-1.5m. Low precipitation ( In regions at the top end of precipitation (maritime), snow insulates the ground from extreme cold and increases spring run off (greater fluvial processes?) Snow often thin & discontinuous. the high  arctic boundary coincides with the northern glacial limit and southern treeline.

Continental climates: Wider range of temperatures that high arcitc, south of treeline and continental. Large temp range disguised by mean (62 degrees in Siberia). Hotter, longer summers that High Arctic - above freezing 5-6 months annually, thaw penetrates 2-3m. Greater precip due to fronts (250-600mm), majority during summer months. Boreal forest supported (taaiga in Siberia) Trees + dry + hot summer = wildfire. Beneath trees, there is less snow due to tree cover and therefore more chance of permafrost due to less insulation that areas with no tree cover.

Tibet Plateau: Low lat + High alt = diurnal and seasonal cycles. Low monthly temp range compared to continental&HA. Low precip similar to high lats. evap 1200-1600mm/yr and precip 200-600mm therefore overall water budget defecit. Veg = steppe tundra more barren that low arctic tundra. Thin snow cover ( Annual fluctuation in solar radiation and air temp creates distinct freeze/thaw regime - this justifies distinction as a seperate periglacial climate.

Alpine Climates: Characteristic of tundra regions, above timberline and mid-lat locations. No as extensive as other PG environments. timberline varies between 2000-4000m elevation depending on location. seasonal and diurnal rhythm of both temp and precip. No harsh winter compared to HA, but mid-lat location imposes the S & D rhythm causing increased oscillation around freezing, increasing FT action. Heavy precip due to maritime or relief factors.

Climates low annual temperature range (10 degrees): Sub-arctic oceanic locations experience a small range due to moderating influence of the sea. (Falkland islands, south Georgia etc..) Low lat alpine locations where diurnal variation wins out over seasonality also exhibit this climate (S America, E Africa, Summit of Mount Loa, Hawaii). Both have shallow penetration of PF.

Antarctica:Special case due to lack of vegetation and high arctic winds, results in redistributed snow affecting the degradation of the ground due to wind action.

General:Cryosphere: anywhere where water is in a frozen state - Snow, Glaciers, ice sheets and shelves. Seasonally frozen ground = frozen for 2 weeks or more. As a zonal phenomenon (across latitudes) from pole to equator it is defined as continuous (80-90%), discontinuous(50-90%), Sporadic(10-50%) and isolated( In the Northern Hemisphere continuous permafrost boundary is approximatley at the MAAT isotherm of -8 degrees. Laptev, East Siberia and the Beufort sea are home to sub-sea permafrost. Relationship between air temp and ground temp can be described using a transfer function known as the n-factor. n-factor = ratio of surface freezing/thawing index to the air freezing/thawing index. Approximatley 0.5 for moist and 1 for dry soils. Snow/veg results in a steep temperature gradient whereas the gradient is lessened in high arctic, barren areas with thin/no snow cover. Zero Curtian effect = when water -> ice latent heat is released prolonging a 0 degrees temperature. Conditions for ZCE: moisture in the active layer & soil isothermal near 0 degrees. Zero annual amplitude occurs at a depth where surface temperature variation is not seen in the permafrost. Difference between MAGST and TTOP is the thermal offset. Frozen water expansion approx 9%. Dissolved minerals (e.g. saline water) can have a depressed freezing point, and when soil exists unfrozen within permafrost due to a depressed freezing point it is called a cryopeg. Freezing degree-day = negative difference between 0 and daily mean temp. Thawing degree-day = positive difference between 0 and daily mean temp. Seasonal and diurnal rhythms dampened with depth in PF. Southern-most limit of permafrost FDD=TDD.

Active Layer Thickness: Decreases with veg/snow cover and at higher latitudes (shorter thaw). Precipitation is also a key factor in ALT. Stefans equation can be used to estimate ALT.

Ground Ice:  Pore, Segregated, Intrusive & Vein. Pore: bonds soil together. Segregated: forms ice lenses via the migration and freezing of pore water. Intrusive: intrusion of water into the frozen zone, seen in sill ice and Pingos. Vein: water collects in ground cracks formed by thermal contraction/FT cycles. Syngenetic ice forms at the same time as sediment is deposited. Epigenetic ice forms post deposition(of sediment). Ice content is defined as the ratio of ice to dry soil.

Periglacial climates

Barry and Gan 2011