Transcript pptへのリンク
吾々の時代： 氷河時代
NSA
氷河時代
Ice Ages
Pleistocene 更新世 この時代をここでは。 2.58
〜 0.0117 M.y. 特に Permian 250-220 M.y. Ordovician 450 M.y. Precambrian 900-650 M.y. (Snowball Earth) 2300 M.y
.
中期更新世以降 0.78 Mya 〜
更新世の 氷河時代 の始まり
氷河時代の証拠 1 ： 氷礫岩 tillite
www.scottishgeology.com/gallery/image02.html
www.eriding.net/media/photos/geograp/_geo_lpp_007_boulder_clay.jpg
boulder
続 Gowganda tillite, Ontario
Rock record of glaciation, this one ~2.3 billion years ago!
1820s
氷河時代の証拠 1’: 氷河性堆積物の再現
• In the early 1800s Jean de Charpentier observed the advance and retreat of glaciers in the Alps and studied the kind of deposits they left behind.
1850s Glacial retreat en.wikipedia.org/wiki/Image:Johann_von_Charpentier.jpg
氷河時代の証拠２ : 氷河地形
www.swisseduc.ch/glaciers/earth_icy_planet/glaciers15-en.html?id=15 Parallel marks show former level of an ice-dammed lake Glen Roy, Scotland • Agassiz amassed more evidence from landforms and boulder clays to support his idea of a Great Ice Age in recent times.
www.geo.umn.edu/courses/4703/Spring00/5-NorthShore/images/striations.jpg
氷河時代の証拠 2’: 擦痕
• In 1840, Louis Agassiz observed similar glacial features in Scotland.
ice scratches en.wikipedia.org/wiki/Image:Louis_Agassiz-2.jpg
• He found scratches on a rocky hillside near Edinburgh like those made by glaciers.
• He argued that Scotland had recently been covered in a thick ice sheet .
氷河時代の証拠 3: 化石
www.colby.edu/geology/gifs/M.nelsoni.jpg
• Fossil discoveries also suggested that climate had recently been much colder .
Pollen • Beetles and pollen grains found in sediments associated with the boulder clays were identified as types known only from the Arctic tundra today.
www.aip.org/history/climate/images/Dryas_octopetala.pollengrain.jpg
Beetles Mammoth • Woolly mammoths found deep frozen in Siberia had fur adapted to tundra life.
仮説：ミランコヴィッチサイクル
Milankovich Cycles
Cool Summers More Important Than Cold Winters 自転軸の傾き Tilt of Axis 公転軌道の離心率 自転軸の歳差運動 Shape of Orbit Precession
ミルティン・ミランコビッチ
Milutin Milanković
1920 年，太陽の放 射による熱現象の 数学理論 Théorie mathématique des phénomènes thermiques produits par la radiation solaire
Axis Tilt
Small Axis Tilt: Mild winters but cool summers. Favors Ice Age Large Axis Tilt: Cold winters but hot summers. Favors Interglacial
Precession: 26,000 year cycle
Shape of Orbit + Precession
Summer at Perihelion (Eccentric Orbit) Cold winters but hot summers. Favors Interglacial Summer at Aphelion (Eccentric Orbit) Near-circular Orbit Mild winters but cool summers. Favors Ice Age
Cause (4): Cycles
en.wikipedia.org/wiki/Image:Milankovitch_Variations.png
• Milanković added up all the orbital wobbles and predicted that ice ages should occur in regular cycles - probably happening every hundred thousand years or so.
ミランコビッチサイクルの証明： 安定酸素同位体比 : 18 O/ 16 O 氷河成長・減衰の指標 16 O 17 O 18 O 天然存在比 天然存在比 天然存在比 0.99757
0.00038
0.00205
特に， 18 O/ 16 O を指標とする。 δ 18 O で示す。
安定酸素同位体比 : 18 O/ 16 O 蒸発は 16 O の方が 容易。 雲の 16 O 量は相対 的に多い。 氷期には，氷河中 の 16 O も相対的に多 く，海水中の 18 O は 相対的に多くなる。 間氷期には，氷河 中の 16 O が相対的 に多い水が海に注 がれて， 18 O が希釈 される。
If we collect a shell made out of CaCO 3 , we can analyze the O 18 :O 16 ratio by the following formula: delta O 18 = [ (O 18 /O 16 sample) / (O 18 /O 16 standard) -1 ] x1000 The standard that your sample is compared to is either one prepared from ocean water or from a fossil standard. Positive delta O 18 values mean that your sample is enriched in the heavy O isotope; negative delta O 18 values mean it’s depleted in the heavy O 18 .
Curve of average O 18 isotope variation over the past 2my based on analysis of deep sea sediment The curve illustrates changes in global ice volume in successive glacial (blue) and interglacial (green) cycles of the Quaternary Period.
Note that this graph does not show fluctuating temperatures, but changes in the dilution of sea water as a result of freshwater influx from melting glacial ice, i.e., this is a climate proxy
氷河地形 diagram1
氷河進出前の河川による山地斜面： 上に凸
氷河地形 diagram2
氷河進出による侵食
氷河地形 diagram3
氷河融解後に出現した氷食による山地斜面： 下に凸
U 字谷と氷河
Franz Josef Glacier
氷 河 2
氷食崖
擦痕
フィヨルドと懸谷 Milford Sound
Ost- und Nordwand des Matterhorn s, an der Licht /Schattengr enze der Hörnligrat
ホルン
圏谷， Kar: 穂高岳の涸沢カー ル
仙丈ｹ岳（南アルプス）山頂： カールとモレーン（堆石）
ティル モレーンの堆積物： glacial till ← 水の礫岩と比較
周氷河地形： 構造土 frost hexagons A blockfield around 4000m on Mount Kenya 凍結融解作用