ESM 203: Ice in the climate system

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ESM 203 Ice in the climate system

• Tom DunneFall 2006

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Global water stores

• Oceans 97.2
• Ice and snowpacks 2.0
• Groundwater (750-4000m) 0.4
• Groundwater (lt750m) 0.3
• Lakes 0.01
• Soil 0.005
• Atmosphere 0.001
• Rivers 0.0001
• Biosphere 0.00004

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Formation of glacier ice

• Metamorphism makes snow denser after it falls
• Water transfer toward bonds sinters crystals
• Melt-freeze cycles further increase snow density
• Where some snow survives melt season, layers pile
  up and squeeze (increase density) of lower
  layers, causing snow to turn to ice
• Typical densities, kg m3

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Ice layers in a glacier (Hindu Kush)

• Each layer represents annual accumulation
• Ice and gas bubbles in layers enable measurements
  of past atmospheric composition and temperature
• d18O in ice (and in ocean sediments) allows
  estimate of temperature at time of snowfall
• ratio of 18O/16O, compared to ocean water
  standard, more 18O during warmer periods
• oceans enriched, ice depleted during glacial
  periods
• Isotopes of otherelements (15N,40Ar) infer
  airtemperature

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Mass balance of a mountain-valley glacier

• More net accumulation at higher elevations
  because
• accumulation (snow fall) is greater
• ablation (snow melt and sublimation) is smaller

Terminus
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Glacier flow

• Ice is a plastic
• Gravity causes it to flow slowly downhill
• Mass balance Accumulation Ablation
• If glacier is in equilibrium
• accumulation ablation (i.e., mass balance 0)
• flow from accumulation zone to ablation zone
• boundaries stable

• If glacier has positive mass balance
• elevation of equilibrium line decreases
• glacier advances (but then area of ablation
  increases)
• If glacier has negative mass balance
• elevation of equilibrium line increases
• glacier retreats (but then area of ablation
  decreases)

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Advance and retreat related to mass balance
Accumulation ? Ablation
equilibrium line
Accumulation ? Ablation
Accumulation ? Ablation
glacier ice
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Types of ice masses (morphological)
Increasing scale

• Cirque all Sierra glaciers today, e.g. Dana,
  Palisade
• Mountain Valley Baltoro (Pakistan), Yosemite in
  Pleistocene
• Piedmont Malaspina (Alaska)
• Mountain icecap Patagonia, Tuolumne in
  Pleistocene
• Continental today only Greenland and Antarctica
• Floating Glacier Bay (Alaska), Ross Ice Shelf
  (Antarctica)

Larger ones generally respond more slowly to
perturbations of their mass balance
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Cirque glaciers Dana Glacier, Sierras
1978 (J. Dozier)
1908, from the Berkeley Geography Collection
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Cirque headwalls in Hindu Kush
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Glacier polish, Tuolumne Meadows
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Mountain glaciers now retreating
Kilimanjaro from Kenya side
Glacier Peak, Cascade Range, WA US Geological
Survey
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U-shaped valley after glacier retreat
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Ice-cored moraine indicating former position of
glacier terminus, Capps Glacier, Alaska
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Retreat of Oori Kalis Glacier flowing out from
the Quelccaya Ice Cap in the Peruvian Andes
(1978-2000)
Prof. L. Thompson, Ohio State Univ.
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Valley glaciers
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Barnard Glacier, Alaska
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Piedmont glaciers Malasapina, Alaska
NASA Space Shuttle and Landsat
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Tidewater glaciers, Glacier Bay, Alaska
US Geological Survey
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Continental ice sheets, Antarctica
NASA
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Ice sheets, shelves
http//www.glacier.rice.edu/
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Floating ice shelf disintegrating Larsen Ice
Shelf, Antarctica (100s-1000s of meters thick)
NASA Landsat 7
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Extent of sea ice change from long-term average
extent
NOAA
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Volume changes of the continental ice sheets now
being measured by satellite using radar and
gravity changes
NASA Radar measurements of ice sheet elevation
changes
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Faster flow from West Antarctica because of
thinning sea ice?

• Bed topography (left) and thinning rate (right)
• Enough to raise sea level 0.24 mm/yr
• (Thomas et al., Accelerated sea-level rise from
  West Antarctica, Science, 8 October 2004)

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Sea level and glacier changes in last 100 years
Sea level increasing 1.8 mm/yr, approximately
half from melting glaciers rest from thermal
expansion of sea water
From Global Change Electronic Edition
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Longer-term oscillations between glacial and
interglacial agesThe Milankovitch (1920)
hypothesis

• Long-term variations in climate depend on
  seasonal and geographic variations in solar
  radiation, which are caused by orbital variations

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Orbital causes of climate variability

• Eccentricity
• period 90100 k years
• orbit varies between more eccentric and more
  circular
• Obliquity
• period 41 k years
• inclination of Earths axis varies from
  21.824.4o
• Precession
• period 21-23 k years
• date of perihelion cycles through calendar

152M km
147M km
July 4
Jan 5
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Long-term variability in ocean ?18O why the
shift from 41 Kyr to 100 Kyr?
41 kyr cycle dominated 1.5-2.5 million years
ago100 kyr cycle dominated in last million years
R. A. Muller G. J. MacDonald, Glacial Cycles
and Astronomical Forcing, Science, 277, 215-218,
July 11, 1997
?18O signal indicates relative volume of ice and
ocean water
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Sudden (9C in 50 yr) Arctic warming at end of
Last Glacial Maximum
Severinghaus and Brook, Science, 1999
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Sudden (9C in 50 yr) Arctic warming at end of
Last Glacial Maximum
Severinghaus Brook, Science, 1999
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Glacier/Ice Sheet web sites

• Byrd Polar Research Center (Ohio State)
• http//www-bprc.mps.ohio-state.edu/
• Lamont-Doherty Earth Observatory Climate Data
  Library
• http//lola.ldgo.columbia.edu81/
• University of Washington Quaternary Research
  Center
• http//weber.u.washington.edu/qrc/
• National Snow and Ice Data Center
• http//nsidc.org/glaciers/