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Palaeoclimate Change SOES 3015
Lecture 11 & 12:
Extreme Climates-3 & 4: P/E boundary ~55 Ma &
Mesozoic OAEs (PAW)
Lecture outline:
• Why we study extreme climates
•
- future projections in geological perspective
Cenozoic climate change
- benthic  O 65Ma to present
- benthic  C 65Ma to present
18
13
• The P/E boundary
-
Faunal crisis & isotope excursions
A new explanation for rapid change
Ongoing debate
www.oceanography.ac.uk
(1) Why we study extreme climates
• future projections in geological perspective
(i) future projections in geological perspective
Question: How high
atmospheric pCO2 by
2100?
Answer: 2 x Present
Question: How does that
compare w/ geological
record?
Answer: Examine the
Vostock 18O & foram
11B records
Courtesy IPCC Technical report.
Reproduced by permission from Macmillan Ltd: Climate and atmospheric history of the past 420,000 years from the Vostok ice core,
Antarctica. J. R. Petit, J. Jouzel, D. Raynaud, N. I. Barkov, J.-M. Barnola, I. Basile, M. Bender, J. Chappellaz, M. Davis,
G. Delaygue, et al. Nature, v. 399, p. 429-436 . Copyright (1999). Not under CC licence.
Reprinted by permisson from Macmillan Publishers Ltd: Atmospheric carbon dioxide concentrations over the past 60 million years. Pearson, P.N.,
Palmer, M.R. Nature, v. 406, p. 695-699. Copyright (2000). Not under CC licence.
Courtesy IPCC Technical report.
(2) Cenozoic climate change
• benthic 18O 65Ma to present
• benthic 13C 65Ma to present
(i) benthic 18O 65Ma to present
Question: Why focus on benthic records?
Answer: They give clean globally representative signals
Question: Why?
Answer: Deep oceans are insulated from large seasonal, latitudinal & geographical
variations in temp & salinity
First order pattern 18O 65Ma to present:
• long-term increase in 18O
• this pattern is dominated by a series of rapid “steps”
From: Zachos, J.C., Pagani, M., Sloan, L.,
Thomas, E.,Billups, K.,(2001) ‘Trends,
rhythms, and aberrations in global climate
65 Ma to present’, Science, v. 292, p. 686–
693. Reprinted with permission from AAAS.
This figure may be used for noncommercial, classroom purposes only. Any
other uses requires the prior written
permission from AAAS.
Question: Do these patterns represent cooling or ice growth?
Answer: Primarily cooling before E/O boundary
Significant ice after E/O boundary
Evidence = presence or absence of IRD (non-quantitative) (more on E/O in next Lec)
(ii) benthic 18O 65Ma to present
First order pattern 13C 65 Ma to present:
• wiggles back & forth between ~ +2.5 & ‰
• 1º Cenozoic peak: Pal. (~58-56 Ma)
• 2º Cenozoic peaks: E/O bdy; O/M bdy & mid-Mio
• 1º Cenozoic min: Plio-Pleistocene
Question: What do these changes represent?
Answer: Mechanisms open to debated but general agreement that reflects global
balance in:
Sedimentary burial of dead Corg (not photosynthesis)
CO2 + H2O = CH2O + O2
(cf. prev Lecs)
Oxidative weathering of dead sed. Corg (not respiration)
Recall that Corg is enriched in 12C
It follows that inc. burial to oxidation of Corg
 inc. 12C extraction from global ocean
 inc. sea water 13C
 inc. marine carbonate 13C
Extreme example = Mesozoic OAEs (oceanic anoxic events)
The Selli Level (Early Aptian ) at Apecchiese Road (SS 257) km 33. The picture was taken during
the fieldtrip of the Cyclostratigraphy Workshop (Perugia, 1989). Property E.Erba.
Sea water 13C driven “heavy” becausec:
13C of Corg ~ –20 ‰ PDB
13C of CO3 ~ 0 ‰ PDB
(cf. EJR lecs)
CO2 + H2O = CH2O + O2
NB above equation indicates a control on climate via CO2
Reproduced by permission of American Geophysical Union: Menegatti, A. P., Weissert, H., Brown, R.S., Tyson, R.V., Farrimond, P.,
Strasser, A., Caron M., High-Resolution δ13C Stratigraphy Through the Early Aptian "Livello Selli" of the Alpine Tethys,
Paleoceanography, v 13, no.5, p. 530–545.19 May 1998 .Copyright [1998] American Geophysical Union.
(3) The P/E boundary
• Faunal crisis & isotope excursions
• A new explanation for rapid change
• Ongoing debate
(i) Faunal crisis & isotope excursions
Question: Why is the P/E bdy there? What makes it special?
Answer : Forams say so
Planktics - dwarf “excursion fauna” evolve for short time
Benthics - suffer a mass extinction
(significant ‘cos these sailed through the K/T bdy)
Question: What happens in the isotope records across the P/E bdy?
Answer: both 13C & 18O show short-term –ve excursions
These excursions are seen in
• deep (benthic) and shallow (planktic) sea water
• high and low latitudes
• marine & terrestrial records
Reproduced by permission of American Geophysical Union: Stott, L., Higher temperature and lower oceanic pCO2:
A climate enigma at the end of the Paleocene Epoch. Paleoceanography, v. 7, No. 4, p. 395. 19 may 1992.
Copyright [1992] American Geophysical Union
18O excursion
• must reflect warming
(formerly Late Paleocene Thermal
Maximum, LPTM)
(Pal greenhouse - no IRD, no ice-caps
at this time)
• most extreme in surface waters at high
latitude & deep waters
• by 5 to 8º C (huge)
Reprinted by permission from Macmillan Publishers Ltd: Correlation between isotope records in
marine and continental carbon reservoirs near the Palaeocene/Eocene boundary. Paul L. Koch,
James C. Zachos, Philip D. Gingerich. Nature, v. 358, p. 319-322. Copyright (1992) Not under
CC licence.
Question: What caused such a dramatic warming?
Answer: Most obvious suggestion = an increase in atms pCO2
Quetion: What might have caused an increase in atms pCO2?
Answer: Correlative –ve 13C excursion is providing big clue
Question: Was there a dec. in burial-to-oxidation balance of Corg??
sedimentary burial of dead Corg
CO2 + H2O = CH2O + O2
(cf. prev Lecs)
oxidative weathering of dead sed. Corg
such that
dec. burial to oxidation of Corg
 dec. 12C extraction from global ocean
 dec. sea water 13C
 dec. marine carbonate 13C
Answer: No:
• acts too slowly (on Ma time-scales)
• would require too big a change in flux of Corg into ocean-atms system
(13C Corg only ~ -20‰ PDB)
(ii) A new explanation for rapid change
Question: Is there a source of C w/ sufficiently low 13C to make the change in
flux reasonable?
Answer: Yes = methane as marine gas hydrates
Question: What are gas hydrates?
Answer: Solid CH4 frozen in “cage” of water molecules:
• stable @ low temperature & high pressure
• form within sediments
along continental margins
• via bacterial processes
(~ -65‰ PDB)
• huge reservoir of carbon
“hidden” from ocean-atms
From: University of Southampton
Dickens (95) uses a geochemical box model to show that we can explain P/E –ve
13C excursion via:
• inject 1018 g CH4 (-65‰ PDB)
• over 104 yr
• represents ~10% est. present reservoir)
Question: Why is this important?
Answer: Provides mechanism for rapid
palaeoclimate change
CH4 + 2O2 = CO2 + 2H2O
(directly analogous to burning of fossil fuel)
This realisation has stimulated a flurry
of new research…
Courtesy of GSA: Dickens, G.R., Castillo, M.M., Walker, J.C.G., A blast of gas
in the latest Paleocene: Simulating first-order effects of massive dissociation of
oceanic methane hydrate. Geology (1997), v. 25, p. 259-262,
(ii)
Ongoing debate
Question: Was the CH4-injected during a single instantaneous event?
Answer: Debate - possibly a series of “steps”
High
lat
Low
lat
From: Bains S., Corfield R.M., & Norris R.D., (1999) Mechanisms of climate warming at the end of the Palaeocene:
Science, v. 285, p. 724-727. Reprinted with permission from AAAS. This figure may be used for non-commercial, classroom purposes
Only. Any other uses requires the prior written permission from AAAS.
Question: How rapid was the inferred CH4-induced warming?
Answer: Injection occurred in a single precession cycle (~20 ka)
Reprinted by permission from Macmillan Publishers Ltd: Carbon cycling and chronology of
climate warming during the Palaeocene/Eocene transition Norris, R.D., Röhl, U. Nature, v. 401,
p. 775 778. Copyright (1999). Not under CC licence.
Question: What was the trigger?
Answer: Debate- mass erosion; sea level fall; deep water warming
Reproduced by permission of American Geophysical Union: Katz, M.E., Cramer, B.S., Mountain,
G.S., Katz, S., Miller, K.G., Uncorking the Bottle: What Triggered the Paleocene/Eocene Thermal
Maximum Methane Release? Paleoceanography, v. 16, No. 6, p. 549–562. December 2001.
Copyright [2001] American Geophysical Union.
Reproduced by permission of American Geophysical Union: Dickens, G.R., O'Neil, J.R., Rea,
D.K., Owen, R.M. Dissociation of Oceanic Methane Hydrate as a Cause of the Carbon Isotope
Excursion at the End of the Paleocene Paleoceanography, v. 10, No. 6, p. 965–971. 5 July 1995
Copyright [1995] American Geophysical Union.
Question: What prevented a runaway
greenhouse?
Answer: Debate- inc. in CO2
draw-down from inc. productivity?
Reprinted by permission from Macmillan Publishers Ltd: Termination of global
warmth at the Palaeocene/Eocene boundary throughproductivity feedback
Bains, S., Norris, R.D., Corfield, R.M., Faul K.L., Nature, v. 407, p. 171-174.
Copyright (2000). Not under CC licence.
Que: What was the link to faunal
turnover?
Ans: Debate- warming? Anoxia?
CCD shoaling?
P/E CH4 injection  inc. CO2
[CO32-] = A – [CO2]
(see prev lec.)
Assuming that alkalinity is constant
over the short event:
inc. [CO2]  dec. [CO32-]
i.e. shoaling of CCD
Courtesy of SGF: Dickens, G.R., (2000), Methane oxidation during the Late Palaeocene
Thermal Maximum. Bull. Soc. Geol. France, v. 171, no. 1, p. 37-39.
Is the P/E a “last Cenozoic fart” following the flatulence of the Mesozoic?
Reprinted by permission of American Geophysical Union: Menegatti, A. P., Weissert, H., Brown, R.S., Tyson, R.V., Farrimond, P.,
Strasser, A., Caron M., High-Resolution δ13C Stratigraphy Through the Early Aptian "Livello Selli" of the Alpine Tethys,
Paleoceanography, v 13, no.5, p. 530–545.19 May 1998 .Copyright [1998] American Geophysical Union.
Some new evidence for –ve 13C
excursions associated with oceanic
anoxic events (OAEs)
P/E boundary event represents the
best palaeoclimate analogue that we
have for the modern anthropogenic
experiment
• rapid warming driven by massive
release fossil fuel
• fall in ocean CO3 saturation
• hidden positive feedbacks?
Courtesy of SGF: Dickens, G.R., (2000), Methane oxidation during the Late Palaeocene
Thermal Maximum. Bull. Soc. Geol. France, v. 171, no. 1, p. 37-39.
Modern hydrate =
14,000 Gton ±?
Organic =
Land biota =
Soil =
Dissolved marine =
3,500 Gton
500
1,500
1,500
Inorganic =
Atmospheric =
Ocean =
30,500 Gton
500
30,000
Global C cycle =
34,00 Gton
P/E injection =
1,500 gton
Anthropgn. Injection =
2,000 Gton
Reproduced by permission of American Geophysical Union: Archer, D., Kheshgi, H., MaierReimer, E., Dynamics of Fossil Fuel CO2 Neutralization by Marine CaCO3. Global Biogeochem.
Cycles, v. 12, No. 2, p. 259–276. 25 February 1998. Copyright [1998] American Geophysical
Union.
What can we learn about climate sensitivity to CO2?
methane hydrate cannot
have been responsible if
CO2 sensitivity was as
assumed (1.5 - 4.5°C)
thus
either P/E resulted from
huge input of CO2
(mechanisms unknown)
From: Pagani, M., Caldeira, K., Archer, D., Zachos J.C., (2006) Atmosphere: An Ancient Carbon
Mystery. Science, v. 314, p. 1556-1557. Reprinted with permission from AAAS. This figure may
be used for non-commercial, classroom purposes only. Any other uses requires the prior written
permission from AAAS.
or climate sensitivity to
CO2 was higher
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