Lec 14: Cryosphere

• Cryosphere


  Frozen water part of the Earth system

  
• Types of cryosphere

  • Ice sheets and ice caps
  • Glaciers
  • Ice shelves
  • Permafrost
  • Icebergs
  • Sea Ice

  
• Permafrost


  Ground stays frozen all year long

  
• Ice Sheet

  Mass of glacial land ice extending more than 50,000 square kilometers, found in Antarctica and Greenland, formed by accumulation of snow that compacts into ice

  
• Ice Cap

  Miniature ice sheet
• Glacier


  "River of ice" formed by accumulation of snow that compacts into ice, in constant slow motion flowing downhill under their own weight, periodically retreating or advancing
• Ice Shelf


  Occur when ice sheets extend over the sea and float on the water

  
• Iceberg


  Massive piece of ice (larger than 5m) greatly varying shape, which may be afloat or aground, formed when chunks of ice calve, or break off, from glaciers, ice shelves, or a larger iceberg

  
• Icebergs


  • They are fresh water since they come from glacial ice
  • About 10,000 to 40,000 icebergs annually
  • They transport freshwater and nutrients
  • Large icebergs are controlled mainly by water currents, while winds become more important to icebergs having high sail

  
• Sea Ice


  Frozen ocean water that forms, grows, and melts in the ocean

  
• Sea ice formation

  1. Ocean water begins to freeze, forming small needle-like ice crystals called frazil

  2. Sheets of sea ice form when frazil crystals float to the surface, accumulate and bond together

  3. In calm conditions, frazil crystals form grease ice and then nilas

  4. In agitated conditions, frazil crystals accumulate into slushy circular disks called pancake ice
• Brine rejection


  When frazil ice crystals form, salt accumulates into droplets called brine, which are typically expelled back into the ocean, raising the salinity of the near-surface water and leading to this water sinking and mixing with the water masses below it
• Stages of sea ice development

  • New ice (less than 10 cm thick)
  • Young ice (10 to 30 cm thick)
  • First-year ice (30 cm to 2 m)
  • Multi-year ice (2+ m)

  
• Pressure ridges and rafting

  • Pressure ridges can form from the pressure exerted on the ice by the force of wind or tide, or from thermal expansion
  • Rafting occurs when two floes are pressed together in such a way that one over-ridges the other in a continuous manner
• Leads


  Narrow, linear regions of open water that form because of the motion of the ice

  
• Polynyas


  More uniform in shape and larger in size regions of open water that form from either upwelling warm water or persistent winds
• Temp. rises

  • Sea ice melts
  • Surface albedo decreases
  • Ocean absorbs more heat
• There is a positive feedback loop between sea ice loss and warming climate
• Ice formed from snow vs. ice formed from seawater freezing are different things

  
• "Ice sheet" and "a sheet of ice" are different things