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

nero

zoic

Cen

ozoi

cQ

uate

rnar

y Holocene

Pleistocene

Pliocene

Miocene

Oligocene

Eocene

Paleocene

Neo

gene

Pal

eoge

ne

Upper

Lower

Cre

tace

ous

Mes

ozoi

c

Tria

ssic

Car

boni

fero

usM

esoz

oic

Per

mia

nJu

rass

ic

Upper

Lower

Middle

Upper

Lower

Middle

Lopingian

Guadalupian

Cisuralian

Upper

Lower

Upper

Middle

Middle

Lower

Mis

siss

ippi

anP

enns

ylva

nian

Pal

eozo

ic

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

bria

n

Upper

Lower

Middle

Llandovery

Wenlock

Ludlow

Pridoli

Upper

Middle

Lower

Silu

rian

Dev

onia

nO

rdov

icia

nP

aleo

zoic

Pha

nero

zoic

Pha

nero

zoic

Asselian

Hadean

Arc

hean

Pre

cam

bria

n Pro

tero

zoic

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 /

Eon

Erat

hem

/ Er

aSy

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