Intrinsic (Earth Bound) Mechanisms
! Earth’s crust is a thin veneer
atop molten rock (mantle)
! Continental crust (2.7 gm/cm2) is less
dense
! Ocean crust (3.2 gm/cm 2) is more
dense
! Lithosphere (crust and upper
mantle) rides over semimolten, higher density (>3.6
gm/cm 2) lower mantle
(asthenosphere 100-350 km)
! Earth’s center comprised of
molten magma rich in Fe +2
Tectonic Plates
! Lithosphere of 15
major plates w/rates
from <1 to 10 cm/yr
! Plates consist of both
continental and
oceanic areas; move
as a rigid unit
! Interactions along plate margins control crustal
features
! Divergent boundaries where plates move apart
! Convergent boundaries where plates collide
! Transform boundaries where plates slide past one another
Tectonic Plate Movement Video
Tectonic Control of CO2 – BLAG
! B L A G
Hypothesis
! Seafloor spreading
& subduction rates
control CO2 input to
atmosphere
! C comes from
reservoir in rock
record
! Changes in
atmospheric CO2
impacts climate
ERNER
AGASA
ND
ARRELS
FAST
SPREADING
arbon
SLOW
SPREADING
BLAG Negative
Feedback Loops
Slow
Seafloor
Spreading
Fast
Seafloor
Spreading
Slow Input
of CO2
Rapid
Input of
CO2
Decreased
CO2 Removal
Decreased
Chemical
Weathering
Reduced
Cooling
Cold Icehouse
Climate (decreased
Temp, Rainfall,
Vegetational cover)
Warm Greenhouse
Climate (incr. Temp,
Rainfall, Vegetation)
Reduced
Warming
Increased
CO2
Removal
Increased
Chemical
Weathering
Closed Loop Carbon Cycling
HCO3- ions
! Atmospheric CO2 stored in dissolved HCO3- ions carried
to oceans via rivers
! Marine plankton use HCO3- to build skeletons
! Skeletons deposited as oozes
! Carbonate sediments subducted, melted, incorporated
! CO2 released to oceans/atmosphere via volcanism
CO2 Removal
The Uplift/
Weathering
Hypothesis
Arethusa & Storm Mts. – Alberta, Canada
! Climate is driven by Chemical Weathering; not a
negative feedback
! Average weathering rate controlled by available
fresh rock & mineral surfaces
! Smaller the weathered particle, greater surface
area for chemical reaction
! Areas of tectonic uplift enhance exposed surfaces
Crowfoot Mountain, Alaska
Mineral Creek, Alaska
Uplift
! Mass wasting removes
overlying debris,
exposing fresh bedrock
! Earthquakes dislodge
rock debris
! Steep slopes foci of
rainfall
! High mountains create
own wet circulation
patterns (monsoons)
! Glacial ice enhances
weathering
! Subduction rates
steady over time; total
amount of high
Steep
Slope
mountain terrane likely
Mass
Mt.
Slopes
Wasting Glaciers Precipitation
constant over time
! Continent-continent
collision result in high
Increased Rock
mountain terrane
Fragmentation
! Natural extent of
exposed rock may set
natural limit on cooling
Increased
intensity due to uplift
Weathering and CO2
Removal
! Chemical weathering
thermostat controlled
by other 99% of
Global Cooling
continental area
UPLIFT
Extrinsic
(Extraterrestrial)
Controls
Aphelion
Perihelion
! Earth’s position
relative to the sun
influences long-term
global climate
! Milutin Milankovitæ
recognized
gravitational
attraction of other
planets affects Earth
! Orbital parameters
effect In sola tion
cycles
cicent
rRadia
Orbital Parametes & Climate
! Eccentricity is
orbital ellipse
! Variation of orbital
elongation on
100ka cycle
! More eccentric =
more insolation
variation
! Less eccentric =
more equitable
! Obliquity is tilt of axial
rotation
! Angle changes from
22.1E to 24.5E
! Variation on 41 ka
cycle
! <Obliquity = seasonal
insolation varies less
! >Greater = more
seasonal variation
! Precession is wobble
around axis
! Major axis of orbital
ellipse rotates around
sun
! Precession of
equinoxes on 22 ka
cycle
! Changes timing of
seasons
Sycophant or Cycle Phase?
Milankoviæ & Ice Sheets
! Summer insolation is weak
! Summer insolation is
strong
! Less radiation in high
latitudes (>65E)
! More radiation in high
latitudes (>65E)
! Less radiation cools
regional climate
! More radiation heats
regional climate
! Reduction in summer
ablation
! Increased summer ablation
! Snow accumulation & ice ! Snow pack melts; ice sheet
sheet growth
shrinks