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The Palaeocene-Eocene thermal maximum: anatomy of a tipping point

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The Palaeocene-Eocene Thermal
Maximum: anatomy of a tipping point
Mike Stephenson, Robert Knox, Melanie
Leng, Chris Vane, Jim Riding
Tipping point
• point at which a slow gradual
change becomes irreversible and
then proceeds with gathering
pace
• point in the evolution of the
earth's climate leading to
irreversible change
• When a small (unnoticed) thing
happens which is enough to
precipitate huge things
happening….which we can’t
repair
Is the climate tipping?
• Some scientists e.g. James Hansen, tipping point already reached – CO2 at
385 ppm
• Some say - tipping point difficult to predict
for non-linear, complex system
• Some say - political slogan - instil fear in
policy makers and largesse in science
funders
Can we stop the tipping?
• Man made global warming - changing the
composition of atmosphere by emission of
carbon dioxide and methane.
• Remedial action - reduce greenhouse gas.
• Is this a reasonable assumption?
Research: understand tipping point
• rates of change in biogeochemical cycles
• change in extreme events not seen in the
last 10k yrs
• negative feedbacks that bring the system
back to normal dynamic equilibrium
Palaeocene-Eocene Thermal maximum:
natural laboratory
Palaeocene-Eocene Thermal
Maximum: why it’s important
• NOW – injection CO2 into atmosphere.
– changes predicted extreme, 5.6° C increase in the
next one hundred years
– CO2 atmospheric concentrations higher than at any
time during the Quaternary.
• PETM
– similar magnitude CO2 and temperature increase
– some of the remnants of the changes are preserved
in the rocks.
• Comparison follows
Comparison: CO2
• Drax B - 7% of England's electricity;
lifetime emission 1 Gt
• China emissions 3 Gt/yr
• Leman Sandstone Formation 3Gt
storage capacity
• Bunter Sandstone Formation 15 Gt
• PETM caused by 1500 Gt of methane
carbon from decomposing gas-hydrate
reservoirs (Sluijs 2006)
• PETM ~ equivalent of 4-8 times the
anthropogenic carbon released
since start of the industrial era
What is preserved?
Clay Layer
Rocks/lithofacies
Forams
Dinoflagellates
Various geochemical evidence
What does it suggest?
Temperature increase
• TEX86 palaeothermometer
• O isotope excursions in foram calcite and
terrestrial carbonates
• Increased Mg/Ca value in forams
• Poleward migrations of tropical marine
plankton, terrestrial plants, and mammal
migrations
Carbon cycle change
• 2.5 – 6 ‰ carbon isotope excursion
• Believed to represent rapid injection of
13C depleted carbon into the global
carbon pool
• Conjunction of warming and excursion:
greenhouse gas cause?
What does
the CIE
excursion
look
like?
high
low
Gradual recovery
Steep beginning
Bass
River,
Sluijs
(2006)
warm
phytoplanton
temp rise
Apectodinium peak and
temperature rise (as indicated
by TEX86) preceded the CIE
Did heating trigger methane
hydrate release leading to the
CIE?
Fig. 2 High resolution records across the onset of the PETM at Bass River, New
Jersey. BC = bulk carbonate, DINO = dinocysts, VPDB = Vienna Pee Dee Belimnite,
mbs = meters below surface. Scales at TEX86 temperatures represent calibrations by
Schouten et al. (2002) for the top bar and by (Schouten et al. (2003) for the lower bar.
both precede
the CIE
Only biogenic
methane (C = 70‰ enough
to create a CIE
of this size
BP Well 22/10a-4
Middle of N. Sea
Well 22-10a/4
• North Sea well - probably the most
expanded section known – chance to
unravel the CIE
• δ13Corg
• Palynology/palynofacies
• Detailed lithofacies
• Organic geochemistry
• Inorganic geochemistry
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