Permafrost

Permafrost

Frozen soil

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Active layer	thaws seasonally
Permafrost	perenially frozen
Ice wedge	pure ice zones

NASA

Permafrost

Frozen soil

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Active layer	thaws seasonally
Permafrost	perenially frozen
Ice wedge	pure ice zones

ADAPT

Permafrost

Most permafrost is in the Northern Hemisphere

Permafrost and methane (CH₄)

Methanogensis in wetlands (permafrost is basically frozen wetland)

• High water table (flooded)
• High flux of organic material
• Waterlogged soils → anoxia
• Methanogenesis requires anaerobic conditions
• Org-C → CH₄ + energy

ESA

Permafrost and methane (CH₄)

• Permafrost methane release slows after first few decades
• Mature bogs (like permafrost!) become fairly minor methane sources

Permafrost and methane (CH₄)

Permafrost degradation is still bad…

Glaciers

Glaciers

A perennial body of crystalline ice (& rock) that flows under its own weight.

Water ice

Flow in crystaline ice

3 main types of glaciers

Mountain glacier

Topographically constrained

Linnébreen, Svalbard [ghe]

Ice cap

Topographically unconstrained

Baffin Island [Sentinel-2]

Ice sheet

Continental ice cap

Southern Greenland [NASA]

Glacial mass balance

Glaciers reflect the balance between

1. Accumulation (snow)
2. Ablation (melting)

Equilibrium line altitude (ELA): accumulation = ablation = 0.

AntarcticGlaciers.org

Internal deformation ± basal sliding

1. Liquid water at the base
2. Soft, deformable sedimentary bed

On top of the glacier: firn

Glaciers have bubbly ice

Beneath the glacier: erosion generates till

Abrasion: grinding bedrock with rock entrained in ice

Plucking: ice/water exploits bedrock cracks → coarse chunks of rock

←←

Wikimedia

Moraine: a large pile of till at a glacier's edge

Glacial periods are dusty

1. Glaciers and ice sheets generate sediment-choked braided rivers
2. Glacial periods are stormier, drier, windier.
3. Strong winds blow dust over great distances.

Wikimedia

Loess deposits: glacial windblown silts

Last glacial maximum (LGM)

Last glacial maximum

Larger ice masses, lower sea levels

Glacial Isostatic Adjustment (GIA)

LGM sea ice extents

Several models, including Pre-Industrial (PI, left). LGM → a lot more sea ice.

Ice shelves

Ice shelves – the floating limbs of ice sheets

Icebergs

Petermann Glacier, northern Greenland (NASA)

Importance of ice shelves

1. Buttressing: the shelf pushes back on the glacier and slows it down.
2. Ice shelf/cliff instabilities — runaway collapse from…
   • Marine ice shelf instability: water penetrating a retrograde slope
   • Marine ice cliff instability: oversteep ice cliffs collapse

Figure: Siegert+ 2020

Ice shelves & ice streams

Ice streams

• Channels of very fast moving ice (meters/day)
• Drain majority of ice sheet volume
• Discussion: What is the relationship between ice streams, ice shelves, and ice sheet mass balance?

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(No ice shelves around Greenland Ice Sheet currently)
Climate Data Store

Sea ice

Sea ice

Multi-year ice (aka "old ice") is multiple years old.

First year ice is ≤ 1 year old.

Sea ice

Fast ice is "landfast" — anchored to the shore, forms with tides.

Drift ice (pack ice) is free-floating.

Drift ice forms in leads

Thick multi-year ice splits apart to form leads, where new ice begins to form on the open water.

Analogous to tectonic divergent margins

Polynya: persistent open water

Young / first-year ice

Nilas

A sheet of ice that bends with the waves

Brocken Inaglory

Frazil ice

Jagged ice crystals in moving water

Wikimedia/NASA

Grease ice

Very thin, soupy layer of frazil ice

Kathy Kueltz

During the first and following years, sea ice thickens by…

Collisions: ice slides over ice

NASA

Pressure ridge

Wikimedia

USGS

Analogous to tectonic convergent margins

Ice floes: loose multi-year ice

As these drift out from the polar regions, they eventually melt.

Seasonal sea ice

Two hemispheres, two seasons!

Sea ice grows/shrinks quickly. Why?

Sea ice in a changing climate

What melts more easily, first-year or old ice?

How might this set up a feedback in a warming climate?

Climate records in ice

Antarctic ice core sites

Greenland ice core sites

Guillevic+ 2013

NEEM	North Greenland Eemian Ice Drilling	2009
NGRIP	North Greenland Ice Core Project	1999
GRIP	Greenland Ice Core Project	1990
GISP(2)	Greenland Ice Sheet Project	1971

↑ You do not need to know this ↑

Annual layers

Annual layers

A person examining layers from individual storm events in a snow pit.

Why are annual layers in the snow/firn thicker than in the underlying ice?

Ice chronology

Ash layers and other "tie points"

UNH / WAIS Divide

Mt. Erebus (Smithsonian)

Oxygen isotopes in water ice

Light isotopes travel further inland.

Preferentialy condense/freeze heavy isotopes → snow

Oxygen & hydrogen isotopes in water ice

Atmospheric gas stored in bubbles

Gas ages vs. water (ice) ages

Snow → Firn → Ice

Gas ages ≈ water (ice) ages

(within uncertainty)

• Historical thought— gas 10²–10³ y younger than ice.
• Better firn compaction models → gas mostly stays put.

Parrenin+ 2013

Vostok Ice Core

Interpreting Vostok ice core data

Ocean-atmosphere-cryosphere-hydrosphere-biosphere
connections

And this holds up on shorter timescales!

Ice sheets across hemispheres (70–20 ka)

Ice sheets across hemispheres

Zoom in on the timing.

Ice sheets across hemispheres

N & S nearly in-phase

Greenland always warms/cools ∼200 years before Antarctica.

An interhemispheric change…

…with a ∼200-year lag.

🤔

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WAIS Divide Project Members, 2015

Polar See-saw

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