1

0

1

2

3

4W

ater

dep

th (

Kilo

met

ers)

Reconstructing Earth Historywith Stable Isotopes & trace

elements of Marine MicrofossilsForaminifera tests~ calcite (CaCOCO3)

MassSpectrometers

CO2

Isotopes:13C/12C 18O/16ONotation: 13C () 18O ()

Ocean Temperature Ocean TemperatureAs T increases, 18Odecreases 1 ~ 4C

Basic Temperature EquationT=16.9-4.0 (18Oc- 18Osw)(Shackleton, 1974)

18O ()-3 -2 -1 0 1 2 3

0

1

2

3

4W

ater

dep

th (

Kilo

met

ers)

Mixed layer planktonicforaminifera

Benthic foraminifera

25 20 15 10 5 0

Temperature (C)

Stable Isotopes & Paleoclimates

O & C Basics Notation Fractionation

Greenhouse Case Study Icehouse Case Study

Who is this person?Dr. Harold Urey

2

Whats an Isotope? Isotopes - of an element - same number of protons (P),

different number of neutrons (N) (from the Greek isos, meaning same, and topos, signifying

place)

nmEm = mass number (A)n = atomic number (protons)A = P + N

16O, 17O, 18OP/N : 8/8, 8/9, 8/10

12C, 13C P/N : 6/6, 6/7

Extranuclear structure remains the same!

What is Isotopic fractionation?

Knowledge of isotopic fractionation is derivedmainly from?

laboratory calibration studies: equilibrium precipitation experiments exchange or kinetic effects between different

phases or speciessupplemented with:

semi-empirical calculations - data and statisticalmechanics

measurement of natural samples whoseformation conditions are well known

partial separation of isotopes between two substancesduring physical and chemical processes

3

Notation for Expressing Isotopic Compositions(abundances)

Delta Value () - differences in ratios Geochemical applications - difference in

absolute isotopic ratios betweensubstances is adequate

more accurately measured thanabsolute ratios

Ratios reported relative to a standard (ref.gas) in the delta notation expressed asparts per thousand or permil ()

10.0, = 1.0%R = absolute isotope ratios (heavy/light)13C/12C18O/16O

A ()= RAsamp RSTD

RSTDx 103

A()= ( RAsampRSTD

-1) x 103

13C()= 13C/12C(samp)!-!13C/12C(std)!

13C/12C(std) x 103

13C()= ( 13C/12C(samp)!

13C/12C(std) -1 ) x 103

If Ra > Rb, heavier, higher, more positive18O, 2H or D, 15N, 34S,

Why not absolute values? convenience: working w/ small differences

(i.e. 13C = 1.1230% 1.1210%) ensures greater consistency over time and between laboratories

-differences can be measured with greater precision

Equilibrium FractionationDefined as a redistribution of isotopes of an element among

various species or compounds aA1 + bB2 aA2 + bB1 where A & B represent two species, subscripts 1 &2 isotopes

that are substituted, a & b # of molesFor example; 1/3 CaC16O3 + H218O 1/3CaC18O3 + H216O

Requirements for Equilibrium? closed system and/or well mixed Stable (on some time-scale that is rate dependent) complete equilibrium is achieved when forward / backward reactions

are equal

Highly temperature dependent !

4

General observations of Equilibrium Fractionation:

Oxidation State: heavier isotope accumulates in species/compound with higher

oxidation statei.e., SO4 -2 (S+6)is enriched in 34S relative to SO3 -2 (S+4) and FeS (S-2)

Multiple phases: higher density accumulates heavier isotope 18OS > 18Ol > 18Og

Condensation - heavier isotope is concentrated in the liquidphase, lighter isotope in the vapor phase

For both 13C and 18O ~ CO2 < HCO3 < CaCO3 Temperature:

Increase T difference in equilibrium isotope compositionsdecreases.

Fractionation factor ( ) - defines the fractionation associated w/equilibrium exchange reaction between two substances.R = N*/N, N*=heavy isotope, 18O/16O

A-B = RARB

1/3 CaC16O3 + H218O 1/3CaC18O3 + H216O CaCO3 -H2O = 1.031 at 25C

General observations concerning can be determined experimentally and theoretically values tend to be close to unity (~1.00xx) sign and magnitude dependent on many factors

temperature (most important) chemical composition chemical structure pressure

5

Conversion of to delta:A=

RARSTD

1

x 103 ()

and

B= RB

RSTD 1

x 103 ()

A-B = RaRb

A-B = A + 1000 B + 1000

Express Ra & Rb in terms of and substitute into;

If the 18Ol of the ocean is 1.0, and the water temperature is 25C,assuming equilibrium, what is the 18Oc of calcite that precipitates fromthis water? c-l = 1.028 at 25C

18Oc = (1.0+103) - 103

18Oc = 29.03

Oxygen Isotopes-Temperature and Ice-volume

most abundant element on earth(gas, liquid, solids)

three stable isotopes16O - 99.763%17O - 0.037518O - 0.1995

omnipresent, involved in mostnaturally occurring geologicprocesses

- sea water- hydrologic cycle- biosphere

geothermometer Partitioning of isotopes is

temperature sensitive

6

Isotope Ratio Measurements1. Gas Source Mass Spectrometers2. Convert Sample to CO2

Carbonates - reaction with 100% phosphoric acid (H3PO4) at

temperature to create CO2CaCO3 + H3PO4 CO2 +H2O + CaHPO4

reactions temperatures - 25-90C advantages of higher temperature:

- increase reaction rates- decreases fractionation difference between carbonates

O-isotope fractionation during reaction CO2-CaCO3 = 1.01025 at 25C

2. Waterequilibration w/ CO2 at a fixed temperature (25C)

Must know the fractionation factor:CO2 -H2O = 1.041 at 25C

H2O >> CO2Standards (18O/16O):

Standard abs. ratio(x106)

18O

v- SMOW Standard Mean OceanWater

2005 (0.43)373

0

v SLAP Stand. Light Ant. Precip -55.5

v PDB Pee Dee Belemnite 2067 (2.1) 28.64 (-2.20PDB)

Conversion - SMOW and PDB scalesSMOW = 1.03086 PDB + 30.86PDB = 0.97002 SMOW - 29.98

7

O-Fractionation Mechanisms phase transitions of water - most

effective means of fract. vapor - liquid - ice

evaporation condensation

Vapor Pressure and, to a lesserextent, Freezing PointDifferences: Mass dependant

H218O (20) < H2O (18) For liquid/vapor: O isotope

fractionation decreases withincreasing temperatureFor 0-350C (Horita & Wesolowski,

1994)1000 ln l-v = -7.685+6.7123(103/T) -

1.6664 (106/T2) + 0.35041(109/T3)

5

6

7

8

9

10

11

12

0 20 40 60 80 100 120

18O/16O Fract. (liquid-vapor)

1000ln a (F&O,77)1000ln a (H&W,95)

1000

ln

l-v

C

8

* O always enriched in the C bearing species.CO2 dissolution (hydrolysis):

CO2 (g) CO2 (d) + H2O H2CO3 H+ + HCO3 H+ + CO3Assuming each species is in isotopic equilibrium with water

a species (19C) 103ln a-H2OH2CO3 38.7HCO3 34.5CO3 18.2CO2 (g) 41.6

Partitioning of O between dissolved C & H2O

Paleothermometry in Marine Carbonates

Isotope Exchange reaction between H2O andHCO3, CaCO3 enriches calcite in 18O.

Ca + HCO3 CaCO3 + H2O + CO2CaCO163 + H2O18 CaCO183 + H2O16

CO3H2O = Rc/Rw = 1.028 at 25C Foraminifers are roughly 28 enriched relative

to seawater- Fractionation can deviate for several reasons!

Vital effects - inclusion of metabolic CO2 Precipitation rates - move away from

equilibrium First temperature equation (Epstein et al. 1953)

TC=16.5-4.3(cc- w) + 0.14(cc- w)2

cc== CO2 at 25C

9

Temperature dependence - fractionation increases with coolertemperatures

1000 ln c-w = 2.78!x!106!

!T2 - 2.89 (3)

(Erez and Luz, 1983).

The fractionation factor c-w(Freidman & ONeil, 1977)

Oxygen Isotopes : Seasonal Variations in Modern Foraminifera

Plankton tows, Bermuda (Williams et al. , 1981, Palaeo3, v.33, p. 71-102)

10

Oxygen Isotopes: Lab and Field studies of Modern Foraminifera

Lab culturing experiments Orb-H2O = 3.19-0.208T

Plankton Tows & Box Cores, Indian Ocean (20N-30S)Orb-H2O = 3.50-0.214T

(Bouvier-Soumagnac et al., 1985, JFR, v.15, p. 302-320)

Oxygen Isotopes: Pelagic Benthic Foraminifera

11

Oxygen Isotopes : Modern Benthic Foraminifera

Box CoresRio Grande Rise, Norwegian Greenland Sea, E. PacificRise(Belanger et al.,1981, Palaeo3, v.33, p.205-220)

C. wullerstorfi Oridorsalis Pyrgo

Oxygen Isotopes: Modern Benthics

Box Cores California margin(Grossman, 1984, Palaeo3, v. 47, p.301-327)

12

Heterococcoliths

Calcidiscus leptoporus Emiliania Huxleyi

Coccoliths: Oxygen Isotopes Culturing studies

multiple species 6 range

Calcite18O variations as afunction of: Growth rate Temperature

Species dependant

Ziveri, Stoll et al., 2003, EPSL, v. 210, p.137

13

Coccoliths: temperature

Ziveri, Stoll et al., 2003, EPSL, v. 210, p.137

Natural Abundances of Oxygen Isotopes: Water & Carbonates

14

O-isotope of precipitation For liquid/vapor: O isotope fractionation increases with decreasing

temperature for 0-100C (Friedman & Oneil, 1997):

Condensation18Ol > 18OvClouds become progressively

depleted in 18O18Ov decreases toward high

latitudesIce-sheet 18O = -30 to -50

O-isotopes Natural Abundances: General Observations Ocean W