The Ice Age VSI

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Ice bergs or ice sheets debate; seabed and ice cores; Milankovitch’s three cycles; global impact of Himalayas.
Author

Stephen J. Mildenhall

Published

2024-03-12

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The Ice Age

  • Parallel Roads of Glen Roy (glacier caused lake shores)
  • Players
    • William Buckland (1784-1856) - famous Oxford lecture, p36; traveled around Scotland w Agassiz
    • Charles Lyell (1797-1875) - drift ice theory p37
    • Louis Agassiz - Swiss, ended at Harvard, Neuchâtel discourse 1836
    • Nick Shackleton (1937-2006) - seabed oxygen isotope dating
    • Willi Dansgaard (1922-2011) - ice cores with CO2 pockets and very detailed dating from annual snow
    • George Cuvier (1769-1832) - French anatomist
  • Adam’s mammoth
  • Erratic boulders : how transported; no rounded edges suggests not carried in river
  • diluvium from flood vs. alluvium from rivers
  • p31 boulder clay from glaciers is not sorted by size [Tides book on relationship between current and max size of particle it can carry]
  • 1840: Agassiz promoted theory; A, B & L presented at Geological Soc
  • Ice Bergs or Ice Sheets debate
  • Milankovitch cycles p92 [procession 19-23kys; obliquity (roll) 41ky; eccentricity (100 and 400ka)
  • Nick Shackleton and Neil Opdyke: ratio of isotopes of O (hotter more evap, greater proportion of heavy O in water; snow mostly lighter isotope; when snow cover melts mix changes abruptly p102 cores of seabed), fosils of foram
  • Concern that temp could in influence result, but S showed that deep sea (not infl by temp) and surface foram had same isotope variations
  • Dating needed magnetic reversals [Brunhes-Matuyama reversal] as periods too long for radio carbon [14C created in upper atmosphere by cosmic rays]; can date 6 generations, 5570 half life
  • p113 fig 25 spectral analysis of marine O isotope record with Milankovitch’s three cycles
  • p114 - longer term dating methods: Uranium-thorium; luminescence; comogenic isotope
  • Ice-raft debris (IRD) and collapse of N American ice fields, Heinrich Events
  • p117 very long term record with ice ages
  • p119 70m year temp change and ice sheet development [currently cold]
    • Himalayas -> rain and increased silicate weathering -> less CO2
    • Isolation of Antarctica; Med dries out; connection at Panama which strengthened Gulf Stream and increased moisture to Europe
  • p121: once set in a glacial mode, the length paced by Milankovitch cycles
  • Dansgaard: O isotopes in ice cores [along with trapped CO2] records temp: as air temp falls, more H2O contains heavy O condense and are lost as precip [based on samples around the world];
  • Ice cores give annual readings(!)
  • p127 charts: 800ky chart of CO2, temp and methane from Antarctica and shorter period for Greenland
  • Dansgaard-Oeschger cycles
  • Global thermohaline [heat/salt] circulation [takes 1000 years to go around!]
  • p130: Youger Dryas cooling

Deets

  • Jamie Woodward
  • Volume 380
  • Published 2014