Permafrost

3 types of ice in permafrost

-pore ice (disseminated in soil) -segregated ice (in horizontal layers of pure ice) -ice wedges (in vertical cracks)

with what is there more unfrozen water?

-silt, clay and organics

what is Stefan's solution

-simple analytical solution to asses how much of the ground has thawed and how much has frozen

freezing point depression due to:

-solute content -confinement in small pore space (capillarity) -proximity to charged particle surface

why is the treelike associated with the continuous-discontinuous boundary?

-thicker snow = warmer ground conditions as snow is an insulator - surface offset

what does bedrock thermal envelope look like?

-wide envelope

heat capacity

energy required to change the temperature of 1m cubed of material by one degree celsius. represented by c

heat definition

form of energy that flows along a gradient from hotter to colder systems. we feel temperature due to the transfer of sensible heat to our bodies

cryotic

ground below zero degrees celsius

what happens as icy permafrost degrades

ground volume decreases unevenly, ground properties change, excess water is released

permafrost

ground which has remained at or below zero degrees celsius for two or more years

does wetness increase or decrease thermal conductivity

it increases it ice increases it again as frozen lets heat escape

active layer

layer of ground above permafrost that freezes and thaws each year

frozen

liquid in the form of ice

temperature definition

measure of the average kinetic energy of individual molecules in matter

describe carbon storage in permafrost

-1400 billion tons of carbon stored in arctic soil and permafrost from dead animals and plants -produces either co2 or ch4

why is there permafrost under water in Hudson's bay?

-due to beringia landbridge - exposed to very cold air temp. during last glaciation - glaciated land was insulated from the cold by glaciers

what are limitations to the thermal envelope equation?

-heat transfer in one dimension only -heat transfer only via conduction -amplitude of temperature wave at the ground surface is symmetrical

describe methane emissions from permafrost

-if no o2 available, organic matter decomposition results in methane release which is about 20times more effective than co2 for greenhouse effect

what controls permafrost thickness

-long time -thermal conductivity - mean annual ground surface temp (climate) -geothermal flow -time (transient vs equilibrium conditions) -how easily material conducts heat

cryosuction

a suction in the pore-space of freezing fine-grained ground due to differences in unfrozen water content

how much freezing occurs upwards

about 20%

a in equation

amplitude

cryopeg

area not frozen at bottom of permafrost

describe ground temperature with increasing depth

as you get further down into the ground, temperature increases

what are the two main drivers of permafrost research?

carbon storage and ice content

what controls the shape of the thermal envelope

composition of the ground

continuous-discontinuous boundary

continuous permafrost (90-100% permafrost) and discontinuous permafrost (10-90%). the treelike and boreal forest boundary often associated with continuous-discontinuous permafrost

Tz in equation

depth

what controls thermal offset

difference in thermal conductivity between frozen and thawed active layer

what does wet soil envelope look like

narrow envelope

surface accretion

peat growth or sediment deposition on top of permafrost

excess ice

permafrost can contain more water in the form of ice than what the soil can hold once thawed

the zero curtain effect

persistence of a nearly constant temperature very close to the freezing point of water during annual freezing (and occasionally thawing) of the active layer

talik

pocket of unfrozen ground

what controls surface offset?

snow - snow warms the earth because it insulates and protects heat from escaping

Ts in the equation

temperature at surface

thermal offset

temperature depression in the upper layer of permafrost, resulting from the combined effects of seasonal differences of thermal conductivity and the operation of non-conductive processes in the active layer

thermal conductivity

the ability of a material to conduct heat

unfrozen water content

the amount of unfrozen water contained in cryptic ground (ground below zero)

depth of zero annual amplitude

the distance from the ground surface downwards to the level beneath which there is practically no annual fluctuation in the annual ground temperature - where max and tmin meet

latent heat

the heat required to convert a solid into a liquid of vapour, or a liquid into a vapour without a change of temperature

southern limit

the limit to how south glaciers can stretch, limits permafrost to the north

what does a trumpet graph/thermal envelope represent

the range in temp and depth - tmin and tmax at different depths

geothermal gradient

the rate of temperature increases with depth below the ground surface

what does the equation calculate

the temperature at different depths

k in equation

thermal diffusivity - shrinks trumpet

t in equation

time

w in equation

what makes it fluctuate