ES 106 Glaciers and Ice Ages Glacier thick mass of ice accumulated over years decades centuries A Function of recrystallization of fallen snow B Types 1 alpine valley a high elevations worldwide b piedmont coalescence of valley glaciers in lowlands 2 ice sheets presently Antarctica and Greenland a Antarctica is 4300 m thick b Contains 2 3 of fresh water and 4 5 of ice c ice cap smaller than sheets C Plastic flow from highlands or from central accumulation area 1 upper surface brittle cracks into crevasses 2 sides affected by friction center moves faster II budget of a glacier A snow falls stays or leaves 1 accumulation zone snow stays a more snowfall than loss due to evaporation melting calving b becomes glacial ice upon recrystallization 2 wastage zone snow leaves a loss exceeds accumulation ablation 1 melting 2 evaporation 3 calving into icebergs into the sea a iceberg mostly submerged b navigation hazard in high mid latitudes b divided from accumulation zone at the snowline B advance vs retreat 1 advance tip further from source area downward or outward a increase in accumulation b increase in rate of movement 2 retreat tip closer to source area a always moving away from source area b ablation exceeding accumulation III glacial erosion A striations and polish 1 plucks rocks from its bed 2 grinds its bed with these rocks abrasion 3 makes the rocks into rock flour B valley glacier landforms 1 changes stream carved drainage a straighter b u shaped instead of v shaped 2 landforms include hanging valley ar te cirque horn I IV Glacial deposition A collectively called drift originated with Great Flood explanation 1 moraines from ice moving material a lateral medial along valley glaciers b terminal end in both types c continental have numerous unique landforms drumlin esker kettle lakes 2 outwash plains beyond reach of glacier V Ice Ages A Earth s climate oscillates between glacial and interglacial states 1 glacial stage more stable than interglacial 2 stable beyond predicted stability conditions due to energy requirement to cross threshold B Characteristics of glacials and interglacials 1 glacial a about every 100 000 years b 10O C worldwide average temperature c CO2 about 200 ppm 2 Interglacial ice remains on Greenland and Antarctica a shorter duration than glacial b 15O C worldwide average temperature c CO2 about 280 ppm C Pliocene Pleistocene 1 Extensive areas of high mid latitudes covered with ice sheets a Most recent period of Ice Age shows up to 20 periods of ice advance and melting in the past 3 million years b Polar landmass of Antarctica has had ice at least 14 million years 2 Area a ice extended into central Midwest central to southern Europe central Asia b some parts of Alaska Siberia not ice covered desert like precipitation protected from flow by mountain ranges c effects 1 drift 2 deranged drainage 3 pluvial lakes 4 changes in sea level D More ancient Ice Ages 1 Karoo a 260 to 350 mya b Lasted 90 million years c Wegener s evidence of continental movement 2 Andean Saharan a 430 to 460 mya b Lasted 30 million years 3 Cryogenian a 630 to 850 mya b Lasted 200 million years c Periods of all Earth covered with glacier 4 Huronian a Over 2 billion years ago b Lasted 300 to 400 million years VI Documentation A Drift deposits 1 moraine and loess 2 four major intervals of ice advance 3 successive advances obliterate previous deposits B loess and marine sediments show better than drift 1 at least 18 counting most recent 2 regular advances over past 2 5 million years C oxygen isotope record 1 two common isotopes of oxygen a oxygen 16 and oxygen 18 are stable not subject to decay b have differing numbers of neutrons in nucleus gives different atomic mass c at colder temperatures more oxygen 18 incorporated into skeletons d also heavier oxygen water less likely to evaporate 1 more oxygen 16 in vapor precipitation storage on land 2 more oxygen 18 left behind in water 3 reinforces the temperature effect 2 oxygen isotope ratio in planktonic organisms show dozens of climate swings over past 3 million years D ice cores contain trapped air record of carbon dioxide content VII Causes A land mass configuration 1 need high latitude land masses to accumulate ice 2 high elevations in westerly wind belt help keep ice on land B reinforcement of temperature changes created by changes in Earth s movement around Sun predictable Milankovich Cycles 1 amount of deviation from circular orbit eccentricity a greater eccentricity causes greater difference in seasons from northern to southern hemisphere 1 more sunlight at perihelion than at aphelion 2 varies between nothing to 6 is 1 7 at present 3 100 000 year cycle and 400 000 year cycle 4 Direction of elongation changes with time too b less results in more consistent seasons 2 change in axial tilt obliquity a degree of tilt of axis of rotation between 22 and 24 5 O b increases contrast of summer to winter temperatures 1 more results in greater seasonal variation of temperatures 2 less has a smaller change in seasonal temperatures c about 41 000 year period of change in obliquity 3 change in direction of tilt precession of axis a Important in its relation to the others superimposed upon them b spin axis oriented toward Polaris at present a complete circle over 25 700 years b axial precession opposite direction from precession of obliquity results in 19 000 to 23 000 year period c effect changes which hemisphere is closer to Sun during summer i causing that hemisphere to have greater seasonal contrast than the other c total amount of sunlight received does not change just the seasonal distribution of it d at present southern hemisphere has greater seasonal contrasts with milder seasons in north 4 Data from sea sediments support the astronomical influence a Oxygen isotope ratios in shells of marine organisms 5 summary glaciation favored by low obliquity low seasonal contrast high eccentricity and precession to have land hemisphere summer at aphelion to reduce melting C CO2 levels which may be partly a function of glaciations VIII Feedbacks in glacial climate system A albedo reflectance by clouds and ice positive feedback loop 1 ice a more ice greater albedo b greater albedo less heating c less heating more ice 2 cloud a cloud seeds aerosol sulfur compounds b elevated during glacial times c source organic algae 1 more algae more sulfur aerosols 2 more sulfur aerosols more clouds 3 more clouds more albedo and more precipitation B carbon dioxide changes 1
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