organic proxies for paleoclimate · 2019-10-29 · organic proxies for paleoclimate sabine lengger...
TRANSCRIPT
Organic proxies for paleoclimate
Sabine LenggerUniversity of Plymouth, UKBETR workshop September 2018, XTBG
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: [email protected]://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