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