geog 415 advanced biogeography: quaternary environments ian hutchinson (rcb 7226) office hours:...
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GEOG 415Advanced biogeography:Quaternary environments
Ian Hutchinson (RCB 7226)Office hours: Thursday 3:00-4:30Office phone: 778.782.3232email: [email protected]
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GEOG 415 - Housekeeping
• Course email: [email protected]• Lecture slides and all handouts will
be posted on the course web site:www.sfu.ca/~ianh/geog415/
• Thumbnails of lecture slides (6/page) available from instructor
• No text
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GEOG 415 - Grades, etc.
•Laboratory assignments: 30%(see schedule)
•Term project: 30%•Final exam: 40%
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Why study Quaternary environments? Reason #1
Modern landscapes, both physical and
biotic (particularly at polar and north
temperate latitudes), have been strongly
influenced by Quaternary glaciations
and associated environmental
changes.
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Why study Quaternary environments? Reason #2
Resource management decisions (e.g. groundwater utilization, peat
extraction, placer mining, soil conservation, habitat management) may be considerably enhanced by an
understanding of glaciology, Quaternary geology, and Quaternary
palaeoclimates
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Reason #3: the Quaternary is the period of hominid radiation
Late Tertiary | Quaternary
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Reason #4: The recent past may hold the key to the near future
A) Is the current increase in global temperature merely a blip, within the domain of “natural variation”?
B) Will global warming produce a super-interglacial?
C) Will global warming shut down oceanic circulation, and initiate a new Ice Age?
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Reason #4 (contd.)
A) Domain of natural variation can be established by analysis of climatic and proxy environmental records for the late Quaternary;
B) Previous “super interglacials” may be good analogues for current ‘global warming’;
C) Phases of abrupt climate change in late Quaternary may provide clues to triggers forcing a switch to another climatic state.
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Ice-Ages in geological history
0 200 400 600 800 1000
Qu
ate
rnary
Perm
o-
Carb
onife
rou
s
Ord
ovicia
n
Vara
ng
ian
Stu
rtian
Gn
ejsö
million years BP
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“Greenhouse” ”Icehouse”
Strong circum-tropical current promotes efficient transfer
of heat to polar areas
Strong circum-polar currents inhibit transfer
of heat to polar areas
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Cenozoic climate decline
Mean annual temperatures in NW Europe and NW North America (reconstructed from pollen) shown in red
[based on Table 1.9 in Goudie (1992) “ Environmental Change”, Oxford. U.P.]
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Tertiary cooling in sub-Antarctic waters: the drift to an icehouse
world
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What prompted Cenozoic climate decline and the onset of
glaciation?Main factors:1. Continental drift
Isolation of Antarctica and initiation of sub-Antarctic oceanic circulation; ice-sheet formationIsolation of Arctic Ocean; sea-ice formation
2. OrogenesisIsolation of continental interiors, particularly of Central Asia, as a result of uplift of the Himalayas and Tibetan Plateau. High altitude areas = more snow cover = high albedo = regional cooling.
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Palaeocene palaeogeography
http://www.scotese.com/paleocen.htm
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Oligocene palaeogeography
http://www.scotese.com/oligocen.htm
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Initiation of glaciation of Antarctica in the early Oligocene: the record
from the Kerguelen Plateau
Kerguelen
Drake Passage(early Oligocene)
Rapid northward movementof Australia after late Eocene
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Uplift of the Tibetan Plateau
Fig. 7.7 in Goudie (1992) “Environmental Change”
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Tertiary cooling leads to Quaternary ice ages
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Climatic decline in the Cenozoic
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So if the Quaternary is defined as the most recent “Ice Age”,
when did it begin?
“perhaps the most stirring impression produced by recent great advances in the study of the Quaternary period is that the
Quaternary itself is losing its classical identity”
Flint, R.F. 1971. Glacial and Quaternary Geology, p. 2
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Locating the Pliocene-
Pleistocene boundary (Ma BP)
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Quaternary time scale (ka BP)
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Glaciations in the Alps:the Penck-Bruckner model
(1909)
“the great interglacial”
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Quaternary temperature‘pulses’
interglacialglacial
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Quaternary palaeothermometer: stable isotopes of oxygen
Evaporation of a water molecule containing18O (‘heavy water’) requires ~12% more energy than one containing 16O.
Condensation of ‘heavy water’ requires ~12% less energy.
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16O/18O ratios recorded in oceanic sediments
Two sources of information: deep-sea cores or ice cores.Oceanic record primarily reflects changes in ice volume; ice-core record primarily reflects changes in temperature
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Calcareous tests of planktonic foraminifera
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18O calculation
18O = (18O/ 16O) sample - (18O/ 16O) standard
(18O/ 16O) standard
x 1000
Results expressed as 0/00, ppt, or ‘per mil(le)’
Standards are:For forams: PDB (Pee Dee Formation belemnite from North Carolina);For water: SMOW (standard mean ocean water) = O 0/00
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Universality of the
oceanic record(hence oxygen isotope stages)
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The ice-core record
ice crystals
trapped air
dust particles?
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Spectral analysisof Vostok -18O time series
Four superimposed pulses (105 ka, 41 ka, 23 ka, 19
ka), butwhat is the
‘pacemaker’?
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Astronomical/celestial mechanics explanations:
James Croll (1821-1890) • Scottish mechanic,
hotelkeeper, life insurance salesman, janitor and scientist
• Argued that greater orbital eccentricity led to colder winters and development of ice sheets in northern hemisphere
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Orbital eccentricity(product of
gravitational pull of other planets)
aphelion perihelion
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Croll’s model
Ice Ages
~30% variation in solar radiation receipt between aphelion and perihelion at maximum eccentricity at
210 ka.
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Milutin Milankovitch
• Serbian physicist; elaborated Croll’s model of effects of periodic variations in Earth orbit:
• 100 ka (eccentricity)• 41 ka (tilt)• 19-23 ka (precession)
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Obliquity: axial tilt varies from 21.8° - 24.4° over 41 ka cycle as a result
of rotational wobble
strongly seasonal weakly seasonal
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Precession of the equinoxes
Precession results from changing position of North Pole. Pole position rotates because the Earth is not a perfect sphere; hence equinoxes change through year. At present northern
hemisphere tilted toward sun ~ at aphelion.
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Effects of astronomical forcings on summer solar radiation receipt at
65°N
glacials = cool northern summers?
interglacials = warm northern summers?
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Synthesis of ocean-core evidence*
* Ruddiman and Raymo 1988. Phil. Trans. Royal Soc., B318, 411-430
late Pliocene (3.4 - 2.4 Ma): ice sheets in northern hemisphere small; extent controlled by small-scale quasi-periodic oscillations.
early (Lower) Pleistocene (2.4 - 0.7 Ma): moderate amplitude climate changes controlled by 41 ka cycle of obliquity.
late (Middle and Upper) Pleistocene (0.7 Ma - present): large amplitude climate changes controlled by 100 ka cycle of orbital eccentricity.
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Solar activity and irradiance
QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.
Image credit: NASA (Catania Astrophysical Laboratory)
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Is global warming a product of increased solar activity?
How do we track solar activity?
10-Be (“beryllium-10”) is a cosmogenic isotope that is produced when high-energy particles bombard Earth’s atmosphere. When the sun is “active” (during periods of increased sunspot activity) its magnetic field protects the Earth and little 10Be accumulates in ice and sediments.
see: Benestad, R.E. (2002) “Solar Activity and Earth’s Climate”. Praxis
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Solar activity and Earth’s climatic phases in the last 1150 yrs
Om Wm Sm Mm Dm
MM
“Medieval warm period” “ Little Ice Age”
New Scientist, Nov. 12, 2003.
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Phases of solar activity in last millennium
Approximate times of sunspot minima (Xm)
AD 1000 - 1050 Om = Oort minimumAD 1280 - 1340 Wm = Wolf minimumAD 1420 - 1540 Sm = Spörer minimumAD 1650 - 1710 Mm = Maunder minimumAD 1795 - 1825 Dm = Dalton minimum
Approximate times of sunspot maxima (XM)
AD 1100 -1230 MM = medieval maximumAD 1900 - 2000… (current maximum)
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Future global temperature change scenarios (A, B, C)
2000 2050 2100
350
700
CO
2 (
pp
m)
B
A
C
+5°
0°
-5°
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Thermohaline circulation I
= ‘The Great Salty”
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Thermohaline circulation IIFormation of Atlantic Deep Water (ADW) takes place in N. Atlantic. Downwelling initiated by density differences between convergent tropical (dense) and polar (light) shallow water masses. Density differences are a product of contrasting temperature and salinities (hence “thermohaline”). ADW formation and circulation is an important control on oceanic structure in the Indian and Pacific Oceans, and hence global climate. Shutdown of the ‘Great Salty’ conveyor may initiate near-glacial conditions in Europe (Paris = modern Spitzbergen?)
see: Broecker, W. 1995. “Chaotic climate” Sci. Amer., November, 62-68
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see: Stocker, T.F. and Schmittner, A. 1997, Nature 388, 862-865.
Collapse of ADW formation at CO2 levels >750 ppm
CO
2 p
pm