organic proxies for paleoclimate · 2019-10-29 · organic proxies for paleoclimate sabine lengger...

Organic proxies for paleoclimate

Sabine LenggerUniversity of Plymouth, UKBETR workshop September 2018, XTBG

sabine.lengger@plymouth.ac.uk

Assistant professor* at the University of PlymouthInterests: Organic biomarkers, proxy development, analytical methodsTime periods: Contemporary Æ DevonianOpen access

Æ EarthArXiV.org

* In the UK, Assisstant professors are called “Lecturer”

Plymouth

Developed in Plymouth: Sea ice proxy IP25

Belt et al. (2013)

Belt et al. (2007)

Overview

1. Lipids: a brief history of organic geochemistry2. Alkenones / UK

37

3. GDGTs / TEX86• Practical

4. Branched GDGTs / MBT/CBT • Practical

5. n-alkanes6. Isotopes!

• Practical

Lipids & brief history of organic geochemistry

1. Lipids – a brief history of organic geochemistry

Lipids: A loosely defined term for substances of biological origin that are soluble in nonpolar solvents. They consist of saponifiable lipids, such as glycerides (fats and oils) and phospholipids, as well as nonsaponifiable lipids, principally steroids.

Lipid membranes – basic structures

Prokaryota

Hopanols

Eukaryota

Sterols

Fatty acids

Diacylglycerols

by Charles West

Types of membrane lipids

Schubotz (2009)

Other “lipids”

• Pigments: adsorption of / protection from radiation• Carotenoids• Porphyrins

• Storage lipids• Alkenones• Long-chain diols (?)

• Transpiration protection• n-alkanes in leaves

Why are lipids good biomarkers?

1. Easy to analyse

2. Recalcitrant

pKa ≈ 50http://web.chem.ucla.edu/~harding/IGOC/S/sigma_bond.html

3. Specific

Eglinton et al. (1962)

Isorenieratene biomarker

Isorenieratane

• Isorenieratane is a biomarker for Chlorobiaceae, bacteria which thrive under anoxic, sulfidic conditions but need light too.

• Photic zone euxinia.

http://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-158-molecular-biogeochemistry-fall-2011/lecture-notes

Isorenieratene

Isorenieratane

Biomarker Tree of Life

Many types of organisms have specific biomarkers

Briggs and Summons (2014)

The analysis of biomarkers

Rockmin 0.1 % TOC

crush

grindPowder

ExtractionElevated temperatureSoxhlet extractionElevated temperature, pressureAccelerated solvent extractionMicrowave extraction Low temperatureBligh Dyer extractionUltrasonic extraction

Gaines et al. (2009)

Analysis of Biomarkers

In which fraction do we expect to find biomarkers?

Hexane/DCM 9:1(Aliphatic

Hydrocarbons)

Hexane/DCM 1:1(Aromatic Hydrocarbons,

ketones)

DCM/Methanol 1:1

e.g.R

R

e.g. e.g.

CO2H

by Charles West

Mixture of compoundsVolatilised

Stationary phase

Compounds separated in time

Heat

Gas flow

Detector

Chromatography

typically 10 – 60 m

Gas chromatogram: aliphatic Hydrocarbon fraction

1615

14

13

12

11

10

1819 20

21

22 23

2425

2627

28 2930

17 n-alkanes usually dominate

Retention Timeby Charles West

CULE

Organic mass spectrometry

• Ionised molecule ÆMolecular ion

• Breaks apart into smaller fragments

• Weight is detected (only positively charged)

• Largest mass Æmolecular mass

MOLECULE

MOLECULE

Ionisation

+•

MOLE• + LECULEMO • +•

Fragmentation

UE+CLLE+CU

FragmentationRearrangement

n-Hexane

8671

5743

29

15

C4H9+

C3H7+

C2H5+

M+∙

Base peak

Branched alkanes

71

127

Straight-chain vs branched alkanes

71

127

m/z 14 series

Which one is the straight chain alkane?

141

57

71

127

43

127

m/z 14 series

AA B

C D

A three dimensional technique

http://people.whitman.edu/~dunnivfm/C_MS_Ebook/CH5/index.html

Recommended ReadingIntroduction to organic geochemistryS. D. Killops and V. J. KillopsBlackwell Pub (2005). Available for free (legally!) at: https://sites.google.com/site/killopsiog/

Echoes of Life: What Fossil Molecules Reveal about Earth History. S. M. Gaines, G. Eglinton and J. Rullkötter. Oxford University Press (2009).

Biomarkers and Isotopes in the Environment and Human History. K. E. Peters, C. C. Walters and J. M. Moldowan. Cambridge Univ. Press (2005).

Recommended Reading

Briggs, D.E.G., Summons, R.E., 2014. Ancient biomolecules: Their origins, fossilization, and role in revealing the history of life: Prospects & Overviews. BioEssays 36, 482–490. https://doi.org/10.1002/bies.201400010

Eglinton, T.I., Eglinton, G., 2008. Molecular proxies for paleoclimatology. Earth and Planetary Science Letters 275, 1–16. https://doi.org/10.1016/j.epsl.2008.07.012

Alkenonesor the serendipitous discovery of a temperature proxy

Discovery of alkenones

• Boon et al. (1978): first ID in sediments, DSDP core from Walvis Ridge, SW Africa – field desorption MS of TLE and TLC fractions

• Identified as ketones with elemental composition of C37H70O(m/z 530) and ~C38H72O (m/z 544)

• De Leeuw et al. (1980): Confirmation of structure as C37-C39 methyl and ethyl ketones in sediments

Discovery of producing organisms

Brassell, Eglinton, Marlowe, Pflaumann, Sarnthein (1986)De Leeuw et al. (1980), Volkman et al. (1980)

Volkman et al. (1980)Identification of same compounds in Emiliania huxleyiMarlowe et al. (1984) Common to Prymnesiophyceae, Degree of unsaturation related to growth temperature. Proposed as markers for E. hux

Emiliania huxleyi

• Class: Haptophyta (Prymnesiophyta)• Order: Isochrysidales• Family: Gephyrocapsaceae• First appearance during Late Pleistocene (ca. 250 ka)• Cosmopolitan, eurythermal, most widespread

coccolithophores• Dominant source of alkenones in open ocean• Isochrysis and Chrysotila limited to coastal environments

• Morphotypes: warm and cold water form

Types of lipids in coccolithophores

http://www.whoi.edu/cms/files/MOG11_molecular_proxies_81764.pdf

The discovery of organic temperature proxies – UK37

Brassell, Eglinton, Marlowe, Pflaumann, Sarnthein (1986)De Leeuw et al. (1980), Volkman et al. (1980)Brassell et al. (1986) Æ Molecular stratigraphy

Relationship in degree of unsaturation and δ18O observed,

Proposed as a molecular marker for sea surface temperature Æ

Correlation between latitude, SST, and UK

37 in quarternary sediments

Gas chromatogram of TLE of Kane Gap sediments

http://www.whoi.edu/cms/files/MOG11_molecular_proxies_81764.pdf

Why is unsaturation related to temperature?

Image: Brock Microbiology

O

O

CH3

O CH3

O

OH

O

O

CH3

O CH3

O

OH

A certain, stable consistency is necessary for membranes

Cells needs to adjust their lipids and use more “oil” when it is cold and more “pork fat” when it is warm

Alkenone unsaturation index• Initial ratio

::

: : :

(Brassell et al., 1986)• Modified ratio

:

: :

(Prahl and Wakeham, 1987)• Calibration

(Prahl and Wakeham, 1987)

(Müller et al., 1998)

• Calibration Error: ± 1 °C in open ocean, temperate and sub-polar waters

Global calibration (surface sediment)

Conte et al., 2006

Other calibration studies

Prahl et al., 1988 Zink et al., 2001

Cultures LakesCranwell et al. (1985): freshwater lake sediments

Application

Ruan et al. (2015)

Sea surface temperature record – Southern Okinawa Trough

B/A warm periods and YD and OD cold periods clearly present

Bayspline

Tierney and Tingley (2018)

Haptophyte evolution

• Alkenones: 100 Myr first occurrence, 56 Ma first application

• E. hux only 250 ka old • Farrimond et al. (1986): Alkenones reported in

Cretaceous black shales• Marlowe et al. (1990): Micropalaeontological and

molecular data suggests genera belonging to family Gephyrocapsaceae were all potential sources of alkenones in sediments deposited since Eocene (45 Ma) • Cretaceous: ancestors of these organisms

Limitations and open questions

• Species assemblages (e.g. coastal vs. open ocean)• Evolution of haptophytes • Preferential degradation (e.g. Sales de Freitas et al., 2017)• Spatial and temporal productivity patterns (e.g. Haug et al. 2005) • Lateral advection

Not always present/working Æ Other SST proxies

Productivity patterns

Haug et al. (2005)

Cooling is observed, but UK

37’ shows warming

Changes in season of production of alkenones Æ shows the summer temperature

3. TEX86

ARCHAEA

Archaea

Bacteria

Archaea Slime mouldsPlants

Fungi

Animals

Membranes of Archaea

Brock (2000) Biology of Microorganisms, 9th edition

Diether(Archaeol)

Tetraether (GDGT)

Archaea have diether and tetraether membrane lipids

Tetraether lipids are membrane-spanning.

Image: Brock Microbiology

What is a GDGT?

Glycerol phytanylbidi glycerol tetraether

G D G T

Isoprenoid

Distributions of archaeal lipids

Schouten et al. (2002) Earth Planet Sci Lett 204, 265-274

Surface sediment, Antarctica

Surface sediment, Arabian Sea

Schouten et al. (2002)

Schouten et al. (2002)

Calibration based on core tops

Schouten et al. (2002)

Calibration“Mesocosm” (Wuchter et al. 2004)

Core-top studies

Tierney (2012)

Tierney and Tingley (2015)Bayesian

Bayesian Calibration

The Bayesian calibration for TEX86 allows the use of probability estimates

Can be used for surface and upper subsurface (upwelling)

Tierney and Tingley (2015)

Application

• Deep time Æ stable molecules

• Earliest application: Sinemurian (Early Jurassic) – 193 Myr

(Robinson et al., 2017)

Arctic Ocean temperatures during the Paleocene-Eocene thermal maximum

Sluijs et al. (2006)

Many Archaea produce GDGTs

Schouten et al. (2013)

And many have not been cultured yet – so we don’t know if they make GDGTs.

TEX86 exported from below the photic zone

Karner et al. (2006)

Subsurface temperature is correlated with surface temperature.

Bias: Export from below photic zone

Tierney et al. (2014)

Data from: Castañeda et al. (2010), Huguet et al. (2006)

In the Eastern Mediterranean, the TEX86 has recorded surface temperature correctly. In the Arabian Sea, subsurface Æ increase in TEX86 when enhance upwelling during cold periods.

Oxygen exposure time

Bias: Deep water export (Arabian Sea)

“Warm” subsurface signal in the Arabian Sea is only preserved under low oxygen conditions

Schouten et al. (2012) Lengger et al. (2014)

Compounds produced in terrestrial environments vs marine environments

BIT index describes the amount of terrigenous vs marine material

Bias: Terrestrial – BIT index

Hopmans et al. (2004)

BIT index

Always needs to be measured

High BIT index can cause too high TEX86temperatures

Weijers et al. (2006)

Bias: Methane seeps – Methane index

In sediments characterised by diffusive methane flux, more GDGT-2 is produced

Methane index: GDGT-2/crenarchaeol

Weijers et al. (2011)

Bias: Benthic production

Benthic production can occur, but does not affect the TEX86

But if SMTZ occurs in sediment, can have local influence

Lengger et al. (2012, 2014)

Exercise TEX86

Naafs et al. 2016Aquilina et al. 2010

4. MBT/CBT – An organic proxy for temperatures in the terrestrial realm

Branched GDGTs are bacterial membrane-spanning tetraether lipids

Branched GDGTs are bacterial membrane-spanning tetraether lipids

Glycerol alkyldi glycerol tetraether

G D G T

branched

br

brGDGTs are diverse and abundant in terrestrial environments

• First discovered in peat and coastal sediments

• Sinninghe Damsté et al. (2000)

• From anaerobic bacteria• Weijers et al. (2006)

• Temperature dependence discovered in soils

• Weijers et al. (2007)

• Source organisms Acidobacteria• Latest: Sinninghe Damsté et al.

(2018)

Can have 1, 2 extra methylations (Æ II, III)Can have 1, 2 cyclopentyl rings (Æ b, c)

Distribution correlates with temperature

https://www.geo.arizona.edu/~jesst/resources/TierneyPSP_GDGTs.pdf

New and improved calibration for soils

De Jonge et al. (2014)

Peat calibration

Naafs et al. (2017)

Other factors

Applications: Loess soil depositsPeterse et al. (2011)

Mangshan loess plateau

MAT varies in phase with NH summer insolation Æonset of

deglacial warming

Applications: Eocene peat

Inglis et al. 2017

Very high temperatures?

Mean annual air temperature by brGDGTs might not be high enough

Maximum: 29 °C

Eocene: higher in the tropics?

Naafs et al. (2018)

Practical MBT

Dang et al. 2014

Naafs et al. 2017

5. n-alkanes

https://www.flickr.com/photos/jritch/4703253208/

St. John’s Wort, Hypericumhttp://aobblog.com/2010/09/nanotechnology-and-self-cleaning-from-plant-leaf-surfaces/

n-alkanes

Eglinton et al. (1962)

C31 n-alkane

C33 n-alkane

C29 n-alkane

Plant waxes are found in many environments

http://www.whoi.edu/cms/files/MOG11_molecular_proxies_81764.pdf

Leaf wax transport

Eglinton and Eglinton (2008)

Terrestrial plants have longer chains

Song et al. (2015)

Terrigenous / Aquatic ratio

C3 vs C4 plants

C4 plants pre-concentrate CO2 and can survive in drier climates (corn, grasses)

Diefendorf et al. (2015)

Average chain length (ACL)

http://www.whoi.edu/cms/files/MOG11_molecular_proxies_81764.pdf

ACL is specific for vegetation type

C3, C4

Gymnosperms/Angiosperms(Diefendorf et al. 2015)

Marine / Terrestrial

Æ Biomarker GuideÆ mixing models

6. Isotopes

Stable carbon isotopesWe define these values as compared to a standard material with defined value of “0” ÆVienna Pee Dee Belemnite (VPDB)

Compound-specific isotopes

Modified from: Elementar Ltd. UK

n-alkane standard: GC-IRMS

With GC-IRMS, we can determine isotopes of a single compound

δ13C of n-alkanes as a proxy for OM source

Marine: more enriched, terrigenous: more depleted

Also: C3 and C4 vegetation and thus dry / wet climate

http://www.whoi.edu/cms/files/MOG11_molecular_proxies_81764.pdf

δ13C values of n-alkanes% of C3/C4 vegetation traces dust input from African continent

Schefuβ et al. (2013)

Problem: Source shiftShift in sources of organic matter can cause a shift in δ13C

http://www.whoi.edu/cms/files/MOG11_molecular_proxies_81764.pdf

δ13C of alkenones as a pCO2 proxy

C37:2 alkenones can be used as a proxy for pCO2 – but many processes, such as a productivity, and nutrients, complicate this proxy system

M. Pagani (2014)

Hydrogen isotopes: the hydrological cycleHydrogen isotopes (δ2H or δ D values) experience fractionation during evaporation and precipitation

http://www.animalmigration.org/stable_isotopes/kinetic_fractionation.jpg

www.isomap.orgwww.waterisotopes.org

δ2H of water varies globally

D/H ratio (δ2H or δD) of leaf wax n-alkanes is related to source water

Sachse et al. (2006)

Sachse et al. (2012)Schefuss et al. (2005)

Application: African hydroclimatePlant-derived C29n-alkaneWetter towards the Holocene climatic optimum

d2H values of etherlipids

Archaeol

Hydroxyarchaeol

GDGT-0

GDGT-1

GDGT-2

GDGT-3

Questions & Discussion

Email: sabine.lengger@plymouth.ac.ukhttp://www.whoi.edu/cms/files/MOG11_molecular_proxies_81764.pdfhttp://www.bris.ac.uk/nerclsmsf/content/gccirmscourse.pdf https://ocw.mit.edu/courses/earth-atmospheric-and-planetary-sciences/12-158-molecular-biogeochemistry-fall-2011/lecture-notes/

Mod. From H. ElderfieldBy J. Tierney