Cryosphere (Too Frozen Water)

TOPICS

How ice formsWhat controls ice dynamics & importanceInteraction of sea and continental ice with

atmosphere over different time scales

IMPORTANCE OF CRYOSPHERE

To climate system – Change in sea ice & snow cover changes albedo &

temperatures Change in glacial ice changes sea level Melting permafrost releases methane Sea-ice formation changes salinity and affects density,

bottom-water formation & deep-ocean circulationTo biosphere -

Challenge of living on frozen ground Meltwater source and reservoir of freshwater

Components of Cryosphere

Continental ice sheets & ice shelvesMountain glaciersSea iceRiver and lake iceSnow coverPermafrost

Time scales relevant to the cryosphere

87% of ice is in Antarctica10% Greenland2.5% ice shelves (mostly Antarctic) If all ice melted sea levels would go up by about 65 meters (213 ft)

Phase Diagram - Water

Triple Point

Critical Point

Ice grows bydepositionfrom gas to solid (snowflake)

Ice grows bydeposition fromwater to ice(graupel)

Ice grows byagglomeration(ice crystals joinTogether)

Dendrite: Common six sided ice crystal / snow flake.Influences interaction with climate system

The shape of ice crystals cause ice to be less dense than liquid water This causes ice to float with about 9% of the ice volume above water (91% below). a.k.a. - the tip of the iceberg.

Snow Cover

Essential for water resources in the western US

Roughly 75% of the Western US fresh water comes from snow pack.

NA snow cover – February 2002High albedo – large number of reflecting surfaces return radiation to space (80-90%)What is the effect on regional energy balances?

January or February have most NH snow cover.10 x more than in summer

Aside from Antarctica the SH has very little snow cover

Figure 1. History of global mean surface air temperature, from NASA

Permafrost

NH permafrost likely to decrease 20-35% by 2050

Carbon balance in the tundra

Methane possibly released from permafrost?

Methane possibly released from permafrost?

Methane change Since 2005

Methane change Since 2005

Methane change Since 2005

Feedback

Arctic warming faster than rest of planet snow and ice-albedo feedback

Positive feedbackPermafrost

MeltingMethane release

Temperature

Methane Clathrate Hydrates

River and Lakes Spring Thaw

Most rivers are thawing earlier and freezing later.

GLACIERS AND ICE SHEETS

Glaciers begin when snow accumulation is greater than snow melt

Glacier Formation

Pressure Sintering –with increasing density snow is compacted and crystals fuse together

Density Differences

New snow – 50-70 kg/m3

Firn – 400-800 kg/m3

Glacial Ice – 850-900 kg/m3

Low permeability Flows under own weight

Types of Glaciers

Alpine or Mountain Small Confined to mountainous

valleysContinental

Large Unconfined by topography

Glacier Flow

Plastic Deformation – Flow due to high pressure

Basal Sliding – glacier slides over the bed due to presence of liquid water or unconsolidated material

Ice flow speed increases with distance above ground - flow at base equals zeor, ice frozen to the bed

Side view

top

Top view:

Ice flow increases with distance from valley walls.

Friction at the sides reduces flow

Basal melt (or unconsolidated material) can provide a lubricant to increase total ice flow

Ice flow increases with increasing tilt of the mountain

Air bubbles trapped in ice can reveal atmospheric composition in the past (up to about 800,000 yrs)For long term climate reconstruction – take cores from part of ice cap not moving

Accumulation: Snow persists through summer &builds upAblation: Melt, sublimation, loss from wind, loss from flowEquilibrium line: Accumulation = Ablation

When accumulation is greater than ablation in a certain zone the ice sheet :a) Growsb) Shrinksc) Stays the same size

Sublimation or calving

When accumulation is greater than ablation in a certain zone the ice sheet :a) Growsb) Shrinksc) Stays the same size

Sublimation or calving

Alpine Glaciers

Milk Lake glacier 1988

Milk Lake 2009

Glaciers around the world are in retreat

Greenland Ice Sheet (Land Ice)

From GRACESee The State of the Greenland Ice Sheet and Gravity Recovery And Climate Experiment

Right: Mass change distribution (2002-2009) across the ice sheet as determined by GRACE observations.

2010 was an exceptional year for Greenland’s ice cap. Melting started early and stretched later in the year than usual. Little snow fell to replenish the losses. By the end of the season, much of southern Greenland had set a new record, with melting that lasted 50 days longer than average.

West Antarctic Ice Sheet (Land Ice)East Antarctica is Now Losing Ice

350 Gt – 1 mm sea level riseBoth Antarctica and Greenland have been losing ice over the past 8 years.

Sea Ice

What happens to the water level when the ice melts?

a. Overflowsb. Goes downc. Stays the same

Sea Ice

What happens to the water level when the ice melts?

a. Overflowsb. Goes downc. Stays the same

Sea Ice

Importance Ice-albedo feedback Bottom water formation Changes affect polar ocean climate

These effects dominate high-latitude response to increasing atmospheric CO2 levels in cgolbal climate models

Formation of Sea Ice

When temps reach -1.8 °CThickens when new ice freezes onto the

bottom of the ice pack (~1 m every winter)At high latitudes persists during summerPermanent thickness

~5 m in Arctic ~0 m very little survives summer

Seasonal Ice Cover range

Northern Hemisphere Doubles Summer ice extent

decreasing drastically

Southern Hemisphere 5 fold increase

From: http://earthobservatory.nasa.gov/Features/WorldOfChange/sea_ice.ph0p The yellow outline on each image shows the median sea ice extent observed by satellite sensors in September and March from 1979 through 2000.

Sept 2011

From: http://earthobservatory.nasa.gov/Features/WorldOfChange/sea_ice_south.php

http://nsidc.org/arcticseaicenews/2011/020211.html

Sea ice movesIn a constant state of motionMoves faster than land ice2 features of circulation: Transpolar Drift (ice lasts 5 yr) Beaufort Sea Gyre (ice lasts longer)

Sea Ice Drift in the Arctic

Ice Floes

Ice moved by wind and currents Form pressure ridges, leads and polynii

Always small amount of open water (even in winter) Importance

Open water allows for production of ice Release salt to upper ocean, increasing density

Impacts Arctic energy budget Positive ice-albedo feedback Heat loss (100x that of ice) from water to atmosphere

Ice-Atmosphere Interactions

Ice cover modifies atmospheric & oceanic circulation

Formation of NADW (drives thermohaline circulation)

Ice-albedo feedback