Father of Glacial theory. First investigations of glaciers and mountain geology,

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1 First investigations of glaciers and mountain geology, Glaciation happens! -- Historical perspective It happens in cycles -- How do we know this? What are Milankovitch cycles? Sub-Milankovitch change Abrupt change Observation of processes -- striations and ridges of mud and boulders Father of Glacial theory Jean L. R. Agassiz, James Hutton -- identified erratics in Jura mountains Perraudin, peasent, infers alpine glaciation Venetz discussed Perraudin s ideas at Soc. Of Nat t History Charlies Lyell ( present is the key to the past ) says striations were caused by boulder-ridden ice bergs in Noah s flood. (drift!) Agassiz lectures on the great ice age (Sherman Williams style) Buckland, convinced Britain was glaciated, renounces idea of the Noah s flood Agassiz publishes idea of glaciations Edward Hitchcock, State Geologists, gave lecture on Agassiz s ideas s -- glaciation recognized throughout Europe James Croll published Astronomical theory for ice ages 1

2 Milutin Milancovitch, Serbian, published formulas calculating intensity of solar radiation based on Croll s ideas of orbital forcing Milutin Milankovicʼć( ) Changes in earths orbit around the sun. Varies <.1 % in insolation Changes in earths axial tilt between 21.8 o and 24.4 o Defines the Polar Circle Changes in distance between Earth and Sun in any season Cycles are 19 and 23 kyr, x=21 yrs Source: Zachos et al.,2001 Perihelion in NH winter Orbital changes over the last 800 ka and frequency spectrum Perihelion in NH summer + - July solar radiation anomalies at 10, 65 & 80 N for the last 250ka 2

3 Maximum Minimum LGM Cesare Emiliani O ppm in deep sea sediment foraminifera carbonates over time from 0-600,000 years. Averaged over a large number of cores in order to isolate a global signal. Solar radiation anomalies (top of atmosphere) relative to 1950 values (cal cm -2 d -1 ) Laurentide Ice Sheet extent at 18ka ( 14 C) B.P. 3

4 Laurentide Ice Sheet extent at 12.5ka ( 14 C) B.P. Laurentide Ice Sheet extent at 8ka ( 14 C) B.P. Isochrones on the disintegration of the Fennoscandian Ice sheet Laurentide Ice Sheet extent at 5ka ( 14 C) B.P. Source: Saarnisto & Lunkka

5 Global Sea-level changes (+15-20m in MIS11?) Source: Source: Waelbroeck et al., 2001 Source: Cuffey & Marshall,

6 Stage 3 Sea Level -50 to -90 m Stage 2 Sea Level at ~-135 for nearly 10 ky What do we know..? With glaciation and the build up of ice sheets on land, sea level falls, usually about m With deglaciation, sea level rises as glaciers and ice sheets melt back into the sea. If the climate gets warmer, more ice will melt and sea level will continue to rise. How might such changes in the sea level and ice sheet size be recorded in the ocean? Lambeck et al., 2002, QSR and Nature 6

7 Oxygen (8 protons) 16 O 17 O 18 O 99.8% 0.04% Hydrogen (1 proton) 0.2% 1 H 2 H (Deuterium) 3 H (tritium) 99.98% 0.016% (?bombs) So, can make 9 isotopic combinations of H 2 O, e.g., 18 ( 1 H 16 2 O) to 22 ( 2 H 18 2 O) light water heavy water General Equation: δ 18 O = 18 O/ 16 O sample - 18 O/ 16 O standard x O/ 16 O standard Expressed in per mille ( 0 / 00) Negative values = lower ratios = isotopically lighter (less 18 O than 16 O) Positive values = higher ratios = isotopically heavier (more 18 O than 16 O) In paleoclimate studies 1 H 1 H 16 O to 1 H 2 18 O 18 O isotopic depletion Evaporation of more 16 O Ice Sheet ocean 0 In Sea In Ice Glacials = enriched 18 O depleted 18 O Interglacials = depleted 18 O enriched 18 O Source: Frakes et al.,

8 Source: Zachos et al.,2001 Source: Zachos et al.,2001 Changes in δ 18 O measured can be influenced by many factors! In marine sediments: Ice Volume (enrichment of oceans) Melt water Salinity Vital effects In ice cores: Temperature at time of precipitation Distance of transport Source: Zachos et al.,2001 8

9 LR04 Benthic Stack Holocene Quaternary Pleistocene Pliocene 1st ice-rafted rocks in N. Atlantic & N. Pacific Maureen Raymo Lorraine Lisiecki Lisiecki and Raymo, 2005 in Paleoceanography v. 20, spans 5.3 Myr and is an average of 57 globally distributed benthic δ18o records (which measure global ice volume and deep ocean temperature) collected from the scientific literature. (Eastern Equatorial Atlanti Source: Zachos et al.,

10 Marine isotope stages Marine isotope stages a b c d e a b c d e Termination 1 Termination 2 High sea-level Wisconsin/ Weichselian Würm glaciation Low sea-level interstade stade Last Glacial Maximum (LGM) Source: Martinson et al., 1987 Holocene interglacial (Flandrian) Last interglacial: Sangamon/Eemian (Isotope stage 5e) Source: Martinson et al., 1987 Marine isotope stages a b c d e High sea-level Termination 1 Termination 2 Stadials & interstadials Low sea-level Holocene Interglacial Wisconsinan/Weichselian Glacial Eemian/Sangamon Interglacial Last Glacial Maximum (LGM) Source: Martinson et al., 1987 Source: North Grip Project Members

11 Are there thresholds, or feedbacks, in the climate system, beyond which climate will abruptly (& possibly irreversibly) change? (..& how will increased levels of CO 2 affect these?) Source: Petit et al., 1999 Greenland Summit oxygen isotopes ~6 Source: Stuiver and Grootes 2000 Source: Overpeck et al.,

12 4 more Glacia/IG cycles in Epica cores Source: Rahmstorf, Wikipedia art 12