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The Cenozoic greenhouse to icehouse and anextreme global warming event
1
By Dr. Helen Coxall
Från växthus till ishus och en extrem klimathändelse
Dina lärare
Dr. Helen CoxallLecturer/ Docent in Marine Micropalaeontology
My Research: reconstructing ocean and climate changes during the past 70 million years (using microscopic marine fossils and geochemistry).
Förra veckan:
18/1. Geologin bakom klimatsystemet – Alasdair Skelton
25/1. Från växthus till ishus och en extrem klimathändelse – Helen Coxall
1/2. Den pågående istiden – Sarah Greenwood
8/2. Snowball Earth-hypotesen – Alasdair Skelton
15/2. Sedimentologiska argument för och emot hypotesen – Otto Hermelin
22/2. Livets utveckling och Snowball Earth-hypotesen – Otto Hermelin
1/3. Isotopiska och geokemiska argument för och emot hypotesen – Alasdair
Skelton
8/3. Bevis för och emot hypotesen från Islay och Garvellachöarna – Alasdair
Skelton och Linda Löwhagen 8/3
15/3. Arktiska oceanen – finns det analogier för Snowball Earth-hypotesen under
de senaste årmiljonerna? – Martin Jakobsson – 15/3
23-25/3 eller 27-29/3. Exkursion till Islay, Skottland
5/4. Kan en Snowball Earth händer igen? – Alasdair Skelton
19/4. Tentamen
Ditt schema
25/1. Från växthus till ishus och en extrem klimathändelse – Helen Coxall
Course textbook reading
Earth's Climate: Past and Future, Ruddiman, 2013,
W.H. Freeman, 3rd ed.
ISBN: 9781429255257:
Chapters 6 and 7, Zachos et al., 2001; 2008
5
OutlineTo understand the significance of Snowball Earth we have to understand the wider range of climate variability on Earth:
• Trends in Earth’s climate over the past 800 million years: greenhouse and icehouse climate modes (tectonic scale climate variability), the δ18O proxy
STUDY THE RECENT GEOLOGICAL PAST WHERE DETAILS ARE BEST RECORDED
• Earth’s last global greenhouse; (orbital scale climate variability) evidence, cause.
• An extreme climate warming event: warming, ocean acidification & carbon release (sound familiar?) 56 million years ago
• End of the last greenhouse climate, shift into the modern icehouse-Stage 1: cooling & glaciation of Antarctica 34 million years ago-Stage 2: more global cooling and glaciation of the northern hemisphere 2-5 million years ago.
• Conclusions: climate modes over geological time and evidence for the principal driving forces of climate from key examples
Pha
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Cen
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Pleistocene
Pliocene
Miocene
Oligocene
Eocene
Paleocene
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Pal
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Upper
Lower
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Mes
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Car
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Per
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Middle
Upper
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Guadalupian
Cisuralian
Upper
Lower
Upper
Middle
Middle
Lower
Mis
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Pal
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MiddleUpper
CalabrianGelasian
PiacenzianZancleanMessinian
Tortonian
SerravallianLanghian
Burdigalian
Aquitanian
Chattian
Rupelian
PriabonianBartonian
Lutetian
Ypresian
ThanetianSelandian
Danian
Maastrichtian
Campanian
SantonianConiacian
Turonian
Cenomanian
Albian
Aptian
Barremian
Hauterivian
Valanginian
Berriasian
Tithonian
Kimmeridgian
OxfordianCallovianBathonianBajocianAalenian
Toarcian
Pliensbachian
SinemurianHettangianRhaetian
Norian
Carnian
Ladinian
AnisianOlenekian
InduanChanghsingianWuchiapingian
CapitanianWordianRoadian
Kungurian
Artinskian
Sakmarian
Gzhelian
Famennian
Frasnian
Givetian
Eifelian
Emsian
Pragian
Lochkovian
LudfordianGorstian
HomerianSheinwoodian
TelychianAeronian
RhuddanianHirnantian
Katian
Sandbian
Darriwilian
Dapingian
Floian
Tremadocian
Stage 10
JiangshanianPaibian
Guzhangian
Drumian
Wuliuan
Stage 4
Stage 3
Stage 2
Fortunian
KasimovianMoscovian
Bashkirian
Serpukhovian
Visean
TournaisianTerreneuvian
Series 2
Miaolingian
Furongian
Cam
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Lower
Middle
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Wenlock
Ludlow
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Upper
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Silu
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Pha
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Neo-proterozoic
Meso-proterozoic
Paleo-proterozoic
Neo-archean
Meso-archean
Paleo-archean
Eo-archean
Ediacaran
Cryogenian
Tonian
Stenian
Ectasian
Calymmian
Statherian
Orosirian
Rhyacian
Siderian
Greenlandian
MeghalayanNorthgrippian
U/L
L/EM
0.01170.1260.781
1.80
2.58
3.600
5.333
7.246
11.63
13.82
15.97
20.44
23.03
27.82
33.9
37.841.2
47.8
56.059.2
61.6
66.0
72.1 ±0.2
83.6 ±0.286.3 ±0.5
89.8 ±0.3
93.9
100.5
~ 113.0
~ 125.0
~ 129.4
~ 132.9
~ 139.8
~ 145.0
~ 145.0
152.1 ±0.9
157.3 ±1.0
163.5 ±1.0166.1 ±1.2168.3 ±1.3170.3 ±1.4
174.1 ±1.0
182.7 ±0.7
190.8 ±1.0
199.3 ±0.3201.3 ±0.2
~ 208.5
~ 227
254.14 ±0.07
259.1 ±0.5
265.1 ±0.4
268.8 ±0.5
272.95 ±0.11
283.5 ±0.6
290.1 ±0.26
303.7 ±0.1307.0 ±0.1
315.2 ±0.2
323.2 ±0.4
330.9 ±0.2
346.7 ±0.4
358.9 ±0.4
298.9 ±0.15
293.52 ±0.17
~ 237
~ 242
247.2251.2
251.902 ±0.024
358.9 ± 0.4
372.2 ±1.6
382.7 ±1.6
387.7 ±0.8
393.3 ±1.2
407.6 ±2.6410.8 ±2.8
419.2 ±3.2
423.0 ±2.3425.6 ±0.9427.4 ±0.5430.5 ±0.7433.4 ±0.8
438.5 ±1.1440.8 ±1.2443.8 ±1.5445.2 ±1.4
453.0 ±0.7
458.4 ±0.9
467.3 ±1.1470.0 ±1.4
477.7 ±1.4
485.4 ±1.9
541.0 ±1.0
~ 489.5
~ 494~ 497
~ 500.5
~ 504.5
~ 509
~ 514
~ 521
~ 529
541.0 ±1.0
~ 635
1000
1200
1400
1600
1800
2050
2300
2500
2800
3200
3600
4000
~ 4600
present
~ 720
0.00420.0082
Series / Epoch Stage / Agenumericalage (Ma) Eo
noth
em /
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hem
/ Er
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stem
/ Pe
riod
Series / Epoch Stage / Agenumericalage (Ma) Eo
noth
em /
Eon
Erat
hem
/ Er
aSy
stem
/ Pe
riod
Series / Epoch Stage / Agenumericalage (Ma) System / PeriodErathem / Era
numericalage (Ma)Eo
noth
em /
Eon
Erat
hem
/ Er
aSy
stem
/ Pe
riod
Eonothem / EonG
SS
P
GS
SP
GS
SP
GS
SP
GS
SA
INTERNATIONAL CHRONOSTRATIGRAPHIC CHARTInternational Commission on Stratigraphywww.stratigraphy.org
Colouring follows the Commission for the Geological Map of the World (http://www.ccgm.org)
Chart drafted by K.M. Cohen, D.A.T. Harper, P.L. Gibbard, J.-X. Fan(c) International Commission on Stratigraphy, August 2018
To cite: Cohen, K.M., Finney, S.C., Gibbard, P.L. & Fan, J.-X. (2013; updated) The ICS International Chronostratigraphic Chart. Episodes 36: 199-204.
URL: http://www.stratigraphy.org/ICSchart/ChronostratChart2018-08.pdf
Units of all ranks are in the process of being defined by Global Boundary Stratotype Section and Points (GSSP) for their lower boundaries, including those of the Archean and Proterozoic, long defined by Global Standard Stratigraphic Ages (GSSA). Charts and detailed information on ratified GSSPs are available at the website http://www.stratigraphy.org. The URL to this chart is found below.
Numerical ages are subject to revision and do not define units in the Phanerozoic and the Ediacaran; only GSSPs do. For boundaries in the Phanerozoic without ratified GSSPs or without constrained numerical ages, an approximate numerical age (~) is provided.
Ratified Subseries/Subepochs are abbreviated as U/L (Upper/Late), M (Middle) and L/E (Lower/Early). Numerical ages for all systems except Quaternary, upper Paleogene, Cretaceous, Triassic, Permian and Precambrian are taken from ‘A Geologic Time Scale 2012’ by Gradstein et al. (2012), those for the Quaternary, upper Paleogene, Cretaceous, Triassic, Permian and Precambrian were provided by the relevant ICS subcommissions.
v 2018/08
6
Cenozoic greenhouse to ice
house climate transition (0-70 Ma)
Snowball Earthtime
650-700 Ma
Setting the scene: geologic time
How can we know the climate and temperature in the geological past?
Bild: WyrmshadowBild: BBC
The δ18O proxy for past temperature on Earth
Sturtian glacial tillite (Port Askaig Formation, Islay)
Sedimentological evidence for ice in the rock/ sediment recorde.g. glacial tills, and ice rafted debris
The method is based on the principal that there is atemperature controlled fractionation of oxygen stableisotopes (18O & 16O) into calcium carbonate.
Geochemical evidence: the δ18O proxy for past temperature on Earth
δ18O (oxygen stable isotope ratios) measured in minerals, and fossil skeletons and shells preserved in the geological record is used as a palaeothermometer.
All made ofCaCO3
In isotopically identical waters, calcite (CaCO3) shells precipitated in:-cold water have relatively high δ18O-warm water have relatively low δ18O
δ18O temperature
equation
¬Ka
llare
Va
rmar
e®
Temperaturförändring under geologisk tid
Kenozoikum: d18O: Zachos et al. (2008); T: Hansen et al. (2013)Fanerozoikum: d18O: Veizer et al. (2000); T: Royer et al. (2004)
Neoproterozoikum: d13C: Halverson et al. (2005)
?
Temperatur-förändringenligt proxier
700
600
500
400
300
200
100 0
Miljoner år sedan
?
SnowballEarth
δ18O
d18O som en proxy för klimat
IshusVäxtus
Veizer et al. (2000)
Our icehouseclimate
Cenozoicgreenhouse-icehouse
transitionPalaeolat. distribution of IRDOther glacial deposits
Varm
are
Kalla
re
Running means at various temporal steps
-2
-1
0
1
2
3
4
5
6
051015202530354045505560
d18 O
Miljoner år sedan
IshusVäxthus
Zachos et al. (2008)
Pleistocene glaciations
(nedisningar)Cenozoic
greenhouse-icehouse transition
ForaminiferaShell CaCO3
δ18O
d18O som en proxy för klimat
3
4
5
6
0,00,20,40,60,81,0
d18 O
Miljoner år sedan
Zachos et al. (2008)
Nedisningar
ForaminiferaShell CaCO3
δ18O
d18O som en proxy för klimatIshus
1. δ18O (18O/16O) reflects ocean temperature AND the amount of ice stored on land in glaciers (glaciers store 16O), when the foram was alive (i.e. the isotopic composition of seawater).
2. δ13C (13C/12C) reflects global carbon cycling (12C taken up during photoshynthesis), when the foram was alive.
Foraminifera shell CaCO3 (calcium carbonate)
STUDY THE RECENT GEOLOGICAL PAST WHERE DETAILS ARE BEST RECORDED
Where do the most detailed and continuous δ18O curves for the Cenozoic come from? Answer: Foraminifera (microscope shell-building marine plankton)
GREENLAND
EUROPE
AFRICA
SOUTHAMERICA
NORTH AMERICA
ASIA
AUSTRALIA
ANTARCTICA
INDIAN OCEAN
PACIFICOCEAN
ATLANTIC OCEAN
ARCTICOCEAN
SOUTHERN OCEAN
120°E 150°87°30’
88°00’ N
90°E 120° 150°E 180° 150°W 120° 90° 60° 30°W 0° 30°E 60°
60° S
40°
20°
20°
40°
60°
80° N
0°
DSDP Legs 1–96 ( ), ODP Legs 100–210 ( ), IODP Expeditions 301–348 ( ), IODP Expeditions 349–361 ( )
Where does 0-65 Ma foraminifera δ18O data come from?Answer: Deep sea sediments cores
Fossil foraminifera shells from deep seaSediments: our ‘time machine at the seafloor’
Bio- carbonates, foraminifera:CaCO3
The Cenozoic deep sea d18O climate curve
Also known as the ’Zachos Curve’
after the scientist James Zachos,
Measured on thousands of samples of seafloor-living (benthic) foraminifera from all over the world’s oceans
Modified from Zachos et al., 2001, 2008; Cramer et al., 2009.
James Zachos,University of California
Santa Cruz
24
Summary points 1.
• Over its history the Earth has alternated between warm ‘greenhouse’ and colder ‘icehouse’ climate modes, lasting 10s to up to ~100 million years.
• We are now in an icehouse mode that started 34 million years ago.
• Under an icehouse climate, ice and glaciers exist in polar regions. The size of these glaciers changes giving times of stronger and weaker glaciation: we are currently in an interglacial.
• It is much easier to find geological evidence for the past 100 million years. So we can ask more detailed questions such as: Are greenhouse conditions caused by high CO2?Why did the Earth shift into an icehouse state?
The early Cenozoic greenhouse climate
Cenozoic climatic from deep sea d18O (Zachos et al., 2001, 2008; Cramer et al., 2009).
d18O evidence tells us that the deep ocean, and therefore Earth was much warmer than today.
Artists impression of an Eocene forest 40 Ma: Image from Pinterest
Eocene greenhouse climate geography
Maps: Ron Blakely, NAU Geology: http://cpgeosystems.com/rect_globe.html
Similar to modern with some important differences:• Antarctica still attached to S. America (no Antarctic Circum- Polar Current; ACC)• Water flows from the Atlantic to Pacific across the Panama seaway• Water flowed from the Indian Ocean to the Atlantic through the Tethys seaway
Climate evidence from other sources?• Distribution of fossil and sediment types
and the Earth?• Lets look at the north and south pole.
Antarctica today: MAT: interior : -57�C
coast: -18�C
High southern latitudes: Antarctica today
MAT = Mean annual temperature
Images and fossils: Jane Francis, University of Leeds
Eocene fossils and fossil collecting:The La Meseta Formation of Seymour Island, Antarctica
Fossilized cone of an araucarian conifer. It is beautifully preserved in 3D within a carbonate nodule
Fossilized impression of an angiosperm (flowering plant) leaf.
Fossil evidence suggests that during the early to middle Eocene, Antarctica was covered by Araucaria (monkey puzzle) and Northofagus (silver beech) forests found today in Chile, Tasmania and New Zealand.
Reconstructed Eocene biota of the Antarctic Peninsular, Meseta Formation (Reguero et al., 2002).
Antarctica: early-middle Eocene
Axel Heiberg Island, Nunavut, Arctic Canada
High Northern latitudes: Arctic today
Photo J. Alean, 1977
Ellesmere Island, Nunavut, Arctic Canada
MAT TODAY -16°CGlaciers online · J. Alean · M. HambreyMAT = Mean annual temperature
Arctic: early Eocene Ellesmere Island
Top right: Paleontologist Malcolm McKenna collecting fossils in the Eureka Sound Group rocks on Ellesmere Island, summer 2001 (photo JaelynEberle). Fossil finds: various species of leaves (McIver and Basinger, 1999); molar of a large brontothere (large extinct rhinoceros-like mammal, genus Eotitanops) and upper jaw and dentition of an Arctic tapir (Thuliadantamolar) and (Jaelyn J. Eberle). http://www.thecanadianencyclopedia.ca/ Warmer, wetter early Eocene
Ellesmere Island, (C. Morrow)
Artists reconstruction (Clifford Morrows) of the Ellesmere Island environment during the early Eocene period.
Axel Heiberg Island: Arctic Canada. Mummified forest floor and leaf litter, Eocene (53 Ma)
Ansgar Walk
Swamp cypress, fossilized dawn redwood stump.
Arctic: early Eocene Axel Heiberg Island
45 Ma fossilized forest remains showing the Eocene ‘forest floor’ and a single tree stump; Axel Heiberg Island, west of Greenland.
Traces of vast Eocene swamp forests. Comparable to the swamp-lands of modern Florida
The Axel Heiberg Island fossils indicate a warm sub-tropical place similar to the ‘cypress’ swamplands of Florida today.
Reconstructed latitudinal sea surface temperature (SST) gradients from geochemical proxies: higher global averages & warmer high latitudes
30
35
2
SST
°C Today ‘greenhouse climate’geochemical
estimates ‘proxies’
2. d18O fromfossil planktonic(surface floating)
foraminifera
Bijl et al., 2009 1. Tex86 = TetraEther indeXof tetraethers having 86carbon atoms (algal remains)
Higher seal level: Because there were no large glaciers on Antarctica or Greenland global sea level was ca. 80 m higher than today.
Henk Bruinkhuis, National Geographic
Our modern ‘icehouse Earth’
55 million years ago: Warm Earth
Artists impression of an Eocene forest 40 Ma: Image from Pinterest
Why was it so warm during the early Cenozoic?
This has been/is the subject of much debate and research
Hypothesis 1: Early Cenozoic warmth caused by different geography that directed ocean currents & heat south/north (H1-Tectonics)
• Southern land barriers blocked the cold ACC flow that today isolatesAntarctica, thus warmer waters carrying heat reached Antarctica.
• Warmer world results in more water in the atmosphere (also carrying heat), therefore, stronger heat transport by the atmosphere, more hurricanes.
49 Mapaleogeography
Palaeoceanographicreconstruction derived fromgeneral circulation modelexperiments. The orange starindicates the paleo-geographiclocation of ODP Site 1172 at65°S in the southwest PacificOcean, under the influence ofthe Antarctic-derived TasmanCurrent (TC) (Bijl et al., 2010).
A summary of climate and pCO2 indicators during theCenozoic. Deep-sea temperatures (upper) generallytrack pCO2 (lower), reconstructed from terrestrial andmarine proxies. Error bars = data uncertainties.Symbols with arrows = either upper or lower limits.Vertical grey bar (right axis) = glacial–interglacial pCO2
range from ice cores. Horizontal dashed line =present-day atmospheric CO2 concentration(400 ppm).
Beerling & Royer, 2010
Hypothesis 2: Early Cenozoic warmth caused by higher than modern CO2, i.e. a stronger greenhouse effect (H2-CO2)
Atmospheric pCO2 reconstructions from geological proxies show:
1. Up to 5 x modern CO2 during the warm Eocene (50-35 Ma), probably due to greater tectonic activity and more volcanoes than today (e.g. Atlantic Ocean opening).
2. CO2 dropped ca. 34 Ma and haddecreased to modern levels by 25 Ma.
Solenergi och växthuseffekten
Greenhouse Effect Stronger than moderngreenhouse effect in the Eocene
An extreme climate event 56 million years ago:The Paleocene Eocene thermal maximum (PETM)
Reconstruction of a tropical humid Paleocene-Eocene environment. Illustration by Jason Bourque.
Titanoboa: fossilized remains found in a coal mine in Colombia: Estimated to have reached 10-14 m, required mean annual temperatures of 32°C.
Evidence for the extreme event 56 million years ago1. Foraminifera d18O and d13C decreases in marine
sediment cores from around the world
d13 C
~2 ‰ VPDBd18O decrease
= ~8°C (average)ocean warming
~2 ‰ VPDB�13C decrease
= massive releaseof organic carbon
CARBONISOTOPE
EXCURSION(CIE)
d18 O
Legend: Different deep sea core records measured on variousspecies of benthicforaminifera
A ’blip’ on the curve:the PETM on the
Cenozoic deep sea d18O record
Measured on thousands of samples of seafloor-living (benthic) foraminifera from all over the world’s oceans
Modified from Zachos et al., 2001, 2008; Cramer et al., 2009.
d13 C
~2 ‰ VPDBd13C decrease
= CARBONISOTOPE
EXCURSION (CIE)Reflects a massiverelease of carbonwith a low d13C
signature into theocean-atmosphere
reservoir
d18 O
Legend: Different deep sea core records measured on variousspecies of benthicforaminifera
Evidence for the extreme event 56 million years ago1. Foraminifera d18O and d13C decreases in marine
sediment cores from around the world
~2 ‰ VPDBd18O decrease
= ~8°C (average)ocean warming
Warming and carbon release happened within
8 thousand years
A deep sea core from the south Atlantic Ocean showing a ‘brown’ carbonate-free layer dated to 56 Ma (IODP Leg 208)
90% CaCO3 fossil sediments
< 1% CaCO3 fossil sediments Seafloor (benthic) foraminfieraextinction
Evidence for the extreme event 56 million years ago2. Carbonate sediments are dissolved at the seafloor, sea
floor-living foraminifera go extinct: ocean acidification
The ocean/earthnatural CO2 ‘buffer’
Evidence for the extreme event 56 million years ago3. Land fossils show major changes among animals and plants
• Warmth loving animals and plants spread towards polar regions, new species suddenly appeared and major bursts of evolution occurred.
PETM migration corridorPaleogeographic map showing hypothetical migration routes of Teilhardina during the earliest Eocene (Thierry Smith et al. PNAS 2006).
Timing of migration is obtained by correlations of the δ13C excursion in North America (A), Europe (B), and Asia (C).
Evidence for the extreme event 56 million years ago3. Land fossils show major changes among animals and plants
• In low latitude regions mammals became 50% smaller as an adaptation to high temperatures, some reptiles became bigger.
PETM terrestrial δ13C isotope stratigraphy and land mammal response from the Big Horn Basin, Wyoming, USA.
Gingerich (2003) & Magioncalda et al. (2004).
The PETM δ13C excursion (CIE)is also seen in terrestrial carbonate records; proves the whole Erath C-reservoir was effected.
PETM: The cause & significance to modern climate studies
The combination of the carbon isotope excursion (CIE) and rapid global warming at the PETM imply there was a sudden release of 13C-depleted (12C-enriched) carbon to the atmosphere, which resulted in increased greenhouse gases in the atmosphere, and, therefore increased climatic warming effect due to a stronger ‘greenhouse effect’.
WHERE DID THE CARBON COME FROM?
This is the subject of much debate and research!
Reservoir Type of Carbon δ13C (‰)
Atmosphere Inorganic CO2-6 to -7
C4 plants (most tropical & marsh plants) Organic C -23 to -25
C3 plants (most higher plants) Organic C -9 to -13
Surface ocean Organic C -22
Surface ocean Dissolved inorganic CO21
Deep ocean Organic C -22
Deep ocean Dissolved inorganic CO20
Methane deposits Organic C -60
Coal-fossil fuel Organic C -25
Oil-fossil fuel Organic C -33 to -24
Where did the PETM carbon come from?To answer this, we can look to the carbon cycle and think about the δ13C isotopic signatures of the available carbon reservoirs:
Average reservoir δ13C values (after Ruddiman, 2008).
THEORIES FOR THE SOURCE OF PETM INJECTED CARBON• Combustion of shallowly buried coal or peat on land (Kurtz et al., 2003)
• Increased amounts of volcanogenic methane (Storey et al., 2007; Gutjahr et al., 2017)
• Destabilized methane clathrates (frozen methane, CH4) on ocean margins (Dickens et
al., 1995), due to a ‘pre-’ warming of ocean waters.
PETM: theories on the source of carbon 1
Watermolecule
‘cage’
CH4 gas molecule
• CH4 extreme δ13C composition = -60‰ VPDB, …..compared to organic matter • C-organic δ13C (including fossil fuels, e.g. coal, gas, oil) = -13 to 25 ‰ VPDB
Therefore, less CH4 is needed to produce the global δ13C CIE signal than C-org: Question: Could this happen in our future?
Destabilized methane (CH4) hyrdate (clathrates) on ocean margin by precursor ocean warming or underwater landslides (Dickens et al., 1995)
CH4 is a stronggreenhouse gas.It quickly oxidizesto CO2.
http://www.bgs.ac.uk/research/volcanoes/volcanicConnections.html
PETM: theories on the source of carbon 2Massive release of volcanogenic carbon during North Atlantic Volcanism
and opening of the northeastern Atlantic (CO2 & thermogenic CH4)
Storey et al., 2007;
Gutjahr et al., 2017
Eroded core of a PETM-age (~60 myr old) volcano,
Isle of Rhum, Scotland
The PETM is an important analog for current climate warming because the rates of carbon increase in the atmosphere and temperature increase are inferred to
have similar rates and magnitudes, although our modern experiment could be 10 x faster.
What stopped the PETM? What removed the excess carbon?
Various feed backs:• Increased silicate weathering due to more active
hydrological cycle and higher temperatures (the weathering feedback).
• Oceans took up the CO2 – ocean acidification.• Increased biological productivity on land and in
the oceans.
The recovery took about 170 thousand years.
54
Summary points 2. • The last natural greenhouse climate existed from the Cretaceous period to
the end of the Eocene period, 80-34 million years ago.
• Fossils from Antarctica and the high Arctic provide evidence of warmth loving animals and plants living at the poles.
• Geochemical proxy reconstructions show flatter equator-to-pole temperature gradients and global averages ca. 10°C higher than modern.
• Because there were no large glaciers on Antarctica or Greenland global sea level was ca. 80 m higher than today.
• An even more extreme global warming event occurred ~56 Ma - the PETM. This is considered a near analogue for current human driven global warming.
• The general background warmth of the early Cenozoic and the PETM are associated with evidence for atmospheric CO2 up to 4 x modern.
Onset of the icehouse 34 million years ago
Cenozoic climatic from deep sea d18O
(Zachos et al., 2001, 2008; Cramer et al., 2009).
Stage 1: cooling & glaciation of Antarctica 34 million years ago
Iceho
use
gree
nhou
se
Stage 2: more global cooling and drying and
glaciation of the northern hemisphere2-5 million years ago.
Gradual d18O increase followed by an abrupt
step 34 million years ago
(Zachos et al., 2001, 2008; Cramer et al., 2009).
•Extinctions and increased evolutionary turnoveron land and in the oceans, including
-ocean plankton and shelled-organisms,-reptiles, mammals (‘Grande Coupure’) plants.-warmth loving plants and animalsdisappear from the high latitudes
Stage 1: Evidence for cooling & glaciation ofAntarctica 34 million years ago
•Appearance of ice-rafted sediments (evidencefor ice bergs) in sediment cores close to Antarctica
•Deep sea δ18O increase of ~1.5‰ VPDB – terrestrial ice growth
•Sea level fall: 60-80 m
Antarctica became glaciated within 400 thousand years
Green, forested Antarctica became white ice-covered Antarctica34-35 million years ago
What caused the shift into the icehouse?
This is the subject of much debate and research.
Hypothesis 1: different geography isolated Antarctica;decreased ocean heat transport (H1-tectonics/ ocean gateways)
Southern land barriers opened and the cold ACC began flowing, isolating the continent from low latitude warm currents and warm air, like today.
49 MaPaleogeography,
Modern geography with a full strengthAntarctic circumpolar current (ACC)
Modified from Gasson et al., 2014 and DeConto et al., 2008
A summary of CO2 & climate indicators over last 40 myrs with Antarctic and N. hemisphere glacial thresholds from model inter-comparisons.
Hypothesis 2: high CO2 levels and strong greenhouse effect fell below a ‘threshold’ for Antarctic glaciation 34 million years ago
(H2-CO2)
pCO2 reconstructions and modelling show:
1. CO2 thresholds for glaciation are higher for Antarctica than the Northern Hemisphere ice (the South Pole can be ice covered at higher CO2).
2. Antarctic glaciation threshold depends on which model is used!
3. Eocene CO2 is in the range of model predictions for our atmosphere within 100 years –shows the vulnerability of glacial ice!
Range of IPCC predictions
Future
100 50Years into the future
Antarctic ice sheetN. Hemisphere ice sheet
} Anta
rctic
ice
shee
t
N. H
emic
e sh
eet
Preferred hypothesis, but possibly a combination of
both
Causes of reduced CO2?
• Decreased ocean spreading, less volcanic activity• Increased silicate weathering due to the uplift of
the Himalayas (from ~50 million years ago).
Positive feed backs once glaciation starts:• As the oceans got colder more CO2 could
dissolve in and be held in the oceans.• Stronger ocean circulation in a colder world due
to stronger winds and ocean mixing: more nutrients, more primary production, biology draws down more CO2.
Stage 2: Intensification of the icehouse
Cenozoic climatic from deep sea d18O (Zachos et al., 2001, 2008; Cramer et al., 2009).
Iceho
use
gree
nhou
se
Stage 2: more global coolingand drying and glaciationof the northern hemisphere2-5 million years ago.
Further d18O increase ~3 million years agofollowed the appearance of large-scale d18O swings indicating glacial cycles.
Challenge: large scale north glaciations remove evidence of earlier ones: best evidence is found in the oceans.
Stage 2: Evidence for cooling & glaciation of thenorthern hemisphere 2-5 million years ago
• Appearance of abundant ice-raftedsediments in the North Atlantic.
• Deep sea d18O increase of– shows long termcooling trend through the Miocene to the Pliocene and sharp increases of ~1‰ ~5 million years ago.
• Beginning of sharp large d18O oscillations indicating strong glaciations: glacials and interglacials with distinct cyclicity.
The cause is more uncertain than for Antarctica!
•Extinctions and increased evolutionary turnover on land and in the oceans
Fossils show stronger seasons and cooling especially in the high northern latitudes. Tundra replaces boreal forests in the high Arctic.
Miocene 20 Ma
Hypothesis 1: different geography directed ocean currents north, bringing moisture needed for snow fall and ice
growth (H1- tectonics ocean gateways)
• Uplift of Panama blocks water flow to between the Atlantic and Pacific.• Water is directed northwards on the Atlantic current bringing moisture
needed for snowfall and glaciation.Problem: this would also make the northern hemisphere warm.-Model experiments do not support this as the only reason.
Pliocene geography ~5 million years ago
Modified from Gasson et al., 2014 and DeConto et al., 2008
A summary of CO2 & climate indicators over last 40 myrs with Antarctic and N. hemisphere glacial thresholds from GCM-ISM inter-comparisons.
Hypothesis 2: Atmospheric CO2 fell below a criticallevel allowing cooling and glaciation in the North
Hemisphere (H1- CO2)pCO2 reconstructions from geological proxies show:
1. CO2 estimates indicate near modern CO2 levels (pre-industrial) by 15 Ma.
2. Modeled northern hemisphere ‘threshold’ is lower than Antarctica so why didn’t the large northern hemisphere glaciations start until 0-5 million years ago?
Range of IPCC predictions
Future
100 50Years into the future
Antarctic ice sheetN. Hemisphere ice sheet
} Anta
rctic
ice
shee
t
N. H
emic
e sh
eet Not entirely clear!
Thought to be lots of climate feed backs involved.
Subject of current research.
3
4
5
6
0,00,20,40,60,81,0
d18 O
Last Glacial Maximum,25 thousand years ago
Nedisningar
Pleistocene glacial cycles: Next week Sarah Greenwood
Ishus
Conclusions• To understand the significance of Snowball Earth we have to understand the
wider range of climate variability on Earth.
• We can do this with climate proxy records, and computer simulations. The most detailed evidence comes from the past 60 million years.
• Over its history the Earth has alternated between warm ‘greenhouse’ and colder ‘icehouse’ climate modes. Icehouse climates are less common.
• Shifts into and out of greenhouse and icehouse climates have been linked to to changing palaeogeography AND changes in greenhouse gas concentrations.
• Evidence suggests changes in CO2 were most important. Ocean circulation pathways also seems to play a role (the oceans transport heat to high latitudes).
• Complex feed backs with Earth’s albedo biology, clouds and carbon cycling interact and climate scientists try to unravel these complexities.
• Extreme warming at the PETM involved carbon release to the atmosphere. This is our closest analogue of modern human-made global warming.
Snowball Earth~700 million years ago
Last Glacial Maximum (LGM)25 thousand years ago
Thank you for attention
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