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Cryosphere (Too Frozen Water)

Cryosphere (Too Frozen Water). TOPICS. How ice forms What controls ice dynamics & importance Interaction 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

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Cryosphere (Too Frozen Water)

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  1. Cryosphere (Too Frozen Water)

  2. TOPICS How ice forms What controls ice dynamics & importance Interaction of sea and continental ice with atmosphere over different time scales

  3. 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 circulation • To biosphere - • Challenge of living on frozen ground • Meltwater source and reservoir of freshwater

  4. Components of Cryosphere Continental ice sheets & ice shelves Mountain glaciers Sea ice River and lake ice Snow cover Permafrost

  5. Time scales relevant to the cryosphere

  6. 87% of ice is in Antarctica 10% Greenland 2.5% ice shelves (mostly Antarctic) If all ice melted sea levels would go up by about 65 meters (213 ft)

  7. Phase Diagram - Water Ice grows by deposition from water to ice (graupel) Ice grows by agglomeration (ice crystals join Together) Critical Point Ice grows by deposition from gas to solid (snowflake) Triple Point

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

  9. 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.

  10. Snow Cover Essential for water resources in the western US Roughly 75% of the Western US fresh water comes from snow pack.

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

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

  13. Aside from Antarctica the SH has very little snow cover

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

  15. Permafrost

  16. NH permafrost likely to decrease 20-35% by 2050

  17. Carbon balance in the tundra

  18. Methane possibly released from permafrost?

  19. Methane possibly released from permafrost? Methane change Since 2005

  20. Methane change Since 2005

  21. Methane change Since 2005

  22. Feedback • Arctic warming faster than rest of planet • snow and ice-albedo feedback • Positive feedback Permafrost Melting Methane release Temperature

  23. Methane Clathrate Hydrates

  24. River and Lakes Spring Thaw

  25. Most rivers are thawing earlier and freezing later.

  26. GLACIERS AND ICE SHEETS Glaciers begin when snow accumulation is greater than snow melt

  27. Glacier Formation Pressure Sintering – with increasing density snow is compacted and crystals fuse together

  28. 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

  29. Types of Glaciers • Alpine or Mountain • Small • Confined to mountainous valleys • Continental • Large • Unconfined by topography

  30. 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

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

  32. top Top view: Ice flow increases with distance from valley walls. Friction at the sides reduces flow

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

  34. Ice flow increases with increasing tilt of the mountain

  35. 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

  36. Accumulation: Snow persists through summer &builds up Ablation: Melt, sublimation, loss from wind, loss from flow Equilibrium line: Accumulation = Ablation

  37. Sublimation or calving • When accumulation is greater than ablation in a certain zone the ice sheet : • Grows • Shrinks • Stays the same size

  38. Sublimation or calving • When accumulation is greater than ablation in a certain zone the ice sheet : • Grows • Shrinks • Stays the same size

  39. Alpine Glaciers Milk Lake 2009 Milk Lake glacier 1988

  40. Glaciers around the world are in retreat

  41. Greenland Ice Sheet (Land Ice)

  42. From GRACE See The State of the Greenland Ice Sheetand Gravity Recovery And Climate Experiment Right: Mass change distribution (2002-2009) across the ice sheet as determined by GRACE observations.

  43. 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.

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

  45. 350 Gt – 1 mm sea level rise Both Antarctica and Greenland have been losing ice over the past 8 years.

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