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Unformatted text preview: II. River/Lake Ice, Seasonal Snow Cover, and Permafrost Cover,
Fourth Assessment of the IPCC 1. Permafrost warming in the NH during the 2nd half of the 20th century half Direct effect of increasing air temperature Contribution by insulating effects of snowcover 2. Distribution of Permafrost has changed Moving northward Area likely to decrease by 20%-35% by the middle Area of the 21st century of II. River/Lake Ice, Seasonal Snow Cover, and Permafrost Cover,
Melting of permafrost releases greenhouse Melting gases gases
Melting creates lakes and water-logged soil Anaerobic conditions (low oxygen) Methane producing organisms fluorish Emission could double to over 100 million Emission metric tons per year metric Arctic is already warming faster than the rest Arctic of the globe of III. Glaciers and Ice Sheets III.
a. Formation i. Pressure sintering- ice crystals fuse/ bond 1. Density increases 2. Volume of air decreases 3. Snow glacier ice Snow 4. Hundreds to thousands of years Temperatures well below 0°C Little snow accumulation 5. Condition with frequent melting a. Water percolates down through pack and refreezes b. Speeds up process ii. Parts of glacier 1. Accumulation zone 2. Ablation zone 3. If ice reaches a thickness of 4 km 1. Ice at base starts to melt (pressure) Parts of a Glacier Parts http://seagrant.wisc.edu/glaciers/ III. Glaciers and Ice Sheets III.
b. Glacier Flow i. Alpine and continental glaciers ii. Pressure is slowly applied and stress deforms the ice 1. The ice is frozen to bed The a. Flow is 0 at base a. b. Max flow is aloft 2. Glacier in a valley a. Friction reduces flow on edges b. Max flow is toward center 3. Deformation does not extend up to surface a. Stress not strong enough above 50m b. Surface ice is carried along iii. Glacier slides if: 1. Liquid water present (not frozen to bed) 2. Bed made up of unconsolidated material (high water content) iv. Downslope movement Downslope 1. Plastic deformation 1. 2. Basal sliding Overhead view of an alpine valley glacier showing the relative speed of ice movement. ice flow patterns along the entire length of an idealized alpine glacier. http://www.eoearth.org/article/Glacier?topic=54335 Long cross-section view of an alpine valley glacier showing the relative speed of ice movement. III. Glaciers and Ice Sheets III.
c. Source of Information on Past Climates i. During formation air spaces are sealed off ii. Can determine atmosphere gas concentrations at time of Can formation formation iii. Cant just drill a core anywhere
1. 2. 3. 4.
i. ii. iii. Takes ~50 years to seal off air cavities Present is not present Top of ice core is 50 years older than when the core was obtained For rapidly moving glaciers ice cores tell us
Ice structure Ice dynamic For long-term climate records take core from stationary part of glacier Where to drill an Ice Core? Where IV. Sea Ice and Climate IV.
a. Ice-Climate Interactions http://earthobservatory.nasa.gov/IOTD/view.php?id=42302 http://earthobservatory.nasa.gov/IOTD/view.php?id=49338 http://earthobservatory.nasa.gov/IOTD/view.php?id=49132 http://earthobservatory.nasa.gov/IOTD/view.php?id=49344 http://earthobservatory.nasa.gov/IOTD/view.php?id=49553 http://earthobservatory.nasa.gov/IOTD/view.php?id=49440&src=eoa-iotd a. Ice-Atmosphere Interactions i. Seasonal distribution of sea ice is extreme 1. NH ice almost doubles in size 2. SH is ~5 times larger in winter ii. The summer ice extent in NH has been The iii. Sea ice forms from bottom up 1. ~1m new thickness in winter 2. Melting and freezing on equatorward edges 3. Ice lasts throughout year at higher latitudes 4. Southern ocean ice is much thinner (summer melt) 5. Arctic ocean thickness ~5m iv. Ice distribution 1. Large seasonal range is a response to temperature changes 2. Asymmetric shape a. Continental configurations b. Ocean circulation 3. Movement a. Sea ice moves faster than continental ice b. Ice circulation i. CW gyre ii. Transpolar drift stream iii. ~5 years for ice to flow from Siberia across Arctic ocean IV. Sea Ice and Climate IV. Sea-ice-ocean heat flux feedback Sea-ice-ocean ...
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- Spring '11