Standard: NIST L-SVEC Li (SRM 8545)

Lithium Isotopes

TIMS and MC-ICPMS

Lithium – a trace alkali element (Li+, Na+, K+, Rb+). Conservative in Seawater. Residence time (τ) ~ 1.2 Ma Two stable isotopes: 6Li & 7Li ~17% difference in mass ~92.4% 7Li and 7.6% 6Li

Teng et al., 2007, 2008

Schematic illustration of Li isotope systematics in the hydrological cycle, modified from Elliott et al. (2004).

Tracing weathering processes

Tracing crust/mantle recycling

Schematic illustration of Li isotope systematics in a subduction-zone setting, modified from Zack et al. (2003)

Variation of Li concentrations vs. Li isotopic ratios. Teng et al., 2007

100 Ma Climate Control – Urey’s Tectonic Cycle

Continental Run Off

Sedimentation

Continental Plate

CO2 H2O

CO2 H2O

Uplift Erosion Weathering CO2 Drawdown Cooling Subduction Volcanism Elevated CO2 Warming

Weathering

Sedimentation

Ca2+ + 2HCO3- →

CaCO3 + CO2 + H2O Si(OH)4 → SiO2 + 2H2O

Ca2+ + Si(OH)4

Post-Urey: HT Fluxes & Low Temp. Authigenic

Aluminosilicate Formation: “Reverse Weathering”

Cations+Al+Si 2o-Clays MOR CaCO3 + SiO2 ↔ CaSiO3 + CO2

Subduction

Cenozoic Climate:

CO2 and

weathering feedbacks

Zachos et al., 2001 Benthic Foraminifera

Interpretation: Mixing of continental Sr (silicate weathering > 0.720) with basalt Sr (MORB = 0.703) sources to ocean. Seawater cation composition becomes more “continental” after 40 Ma.

Seawater Strontium Isotopes

Himalayan Orogeny

Urey’s Tectonic Cycle - Where does Li fit in?

Continental Run Off

[Li]UCC= 24 ppm δ7LiUCC=1.7‰

[Li]Silicate >> [Li]Carbonate

FHT= 13

CO2 H2O Weathering

Authigenic Clay Formation And

Low temperature Basalt Alteration

Li → 2º Clays

Subduction

FRiver = 10 δ7LiRiver = 23‰

MOR

Lithium Geochemistry is Lithophilic Lithium cycle is virtually all in silicate rocks and

aluminosilicate clays – none in carbonates

Accepted Value 31.0 ‰ ± 0.5 ‰ Contrast: Almost all igneous rocks on Earth are between 0 and 4‰, so seawater Li is

very heavy

[Li]MORB= 6 ppm δ7LiMORB=3.4‰

FLi in 109 Moles/yr

FReFlx= 6 δ7LiReFlx= 15‰

δ7LiHT= 8.3‰

Seawater Lithium Isotope

Composition

[Li]sw = 26 µM

Accepted Value 31.0 ‰ ± 0.5 ‰

Tomascak et al. (2004) and Millot et al. (2004)

-------------- Contrast: Almost all

igneous rocks on Earth are between 0 and 4 ‰,

so seawater Li is very heavy

Misra & Froelich, Science, 2012

Lithium in Seawater - Present

Seawater [Li] = 26 µM δ7LiSW = 31‰ τ ≈ 1.2 Ma

River Water δ7LiRiver = 23‰

[Li]River = 265 nM δ7LiUCC = 1.7‰, [Li]UCC = 24 ppm

Silicate Reverse Weathering Low Temperature Basalt Alteration and

Sediment Diagenesis

δ7LiSediment = 15‰ δ7LiSediment = δ7LiSeawater - ∆SED

At Steady State; Li Input = Li Output

∆SW-SED = δSeawater - δSediment = 16‰

Subduction Refluxed Lithium

δ7LiReFlx = 15‰ δ7LiReFlx = δ7LiSediment

Hydrothermal Fluid δ7LiHT = 8.3‰

[Li]HT = 840 µM δ7Li�MORB = 3.7‰, [Li]MORB = 6 ppm

G. truncatulinoides Globigerina triloba

Globigerina venezuelana Globigerina cryptomphala Globigerina eocaena Globigerina inequispira spp

Planktonic Forams & Bulk Forams

Orbulina universa N. dutertrei G. triloba

Marginotruncana spp. Hedbergella spp

Foram (calcite) Cleaning Method Reductive - Oxidative - Reductive (hydrazine) (H2O2) (hydrazine) (R-O-R) Cleaned (monitor Ca Na Li Mg Ba Mn Sr….in cleaning sol)

Boyle & Keigwin, 1985 Rosenthal et al., 1997

Li/Ca & δ7Li of Core-top

& Tow Forams

[Li/Ca]SW = 26 µM/10.53 mM = 2.47 x 10-3 mM/M [Li/Ca]Forams = 10.5 x 10-6 µM/M (present day) KD = [Li/Ca]Foram/[Li/Ca]SW = 4.25 x 10-3

[Li]Forams = 1 ppm

Misra & Froelich, JAAS, 2009

DSDP & ODP Sampling Sites

δ7Li of Cenozoic Seawater

Species and Bulk

Specific Foram

Samples

δ7Li Evolution

of Cenozoic Seawater

Five-Point Running Mean

± 2σ

Misra & Froelich, Science, 2012

δ7Li Evolution

of Cenozoic Seawater

δ18O vs. δ7Li

Li, Sr, and Os Isotope Records

of Cenozoic Seawater

Os isotopes from Peucker-Ehrenbrink & Ravizza, GTS (2012)

The Weathering Story

Interpretations • Seawater δ7Li rose by 8-9 ‰ over the Cenozoic (60 Ma today)

• This rise in δ7LiSW requires, all else held constant, a decrease in [Li]INPUT and increase in δ7LiOUTPUT to the ocean driven by:

(a) ~ 20‰ rise in δ7LiRiv (from 3‰ at 60 Ma to 23‰ today)

(b) ~ increase / decrease in only Li river flux cannot cause this rise in δ7LiSW

(c) ~ 80% drop in Li hydrothermal flux over the Cenozoic

(d) ~ 5‰ increase in ∆SW-Sediement (from 11‰ at 60 Ma to 16‰ today)

The early Cenozoic climatic optimum was a result of increased supply of carbon dioxide to the ocean-atmosphere system as well as diminished removal of carbon dioxide from the atmosphere through weathering of silicate rocks. The scarcity of newly uplifted, fresh, weatherable rocks in the hothouse climate led to a slowdown of the negative feedback mechanism of the Urey-Walker-Berner cycle and promoted a temporary runaway increase in the CO2 concentrations of the ocean-atmosphere system on the post-KPg Earth. The absence of evidence from seawater 87/86Sr and δ7Li records to support increased continental weathering rates in this high-CO2 hothouse world indicates that the limiting ingredient was igneous silicates undergoing weathering. despite global high temperatures, high CO2, and high rainfall in the tropics (all of which should accelerate silicate weathering and promote removal of CO2), the physical and chemical weathering rates of the continents were subdued because of low uplift rates.

High atmospheric CO2 concentration, rapid global warming and marine anoxia and euxinia. Enhanced biological productivity and recovery after ~400kyrs

lightest values of the Li isotope ratio (7Li) during OAE2, indicating high levels of weathering—and therefore atmospheric CO2 removal.

Pogge et al., 2013

modelling the observed Li and Sr isotope excursions requires a 4 Myr 20% increase in the hydrothermal flux and a 200 kyr pulse of enhanced riverine Li flux from basaltic rocks coupled with very light (river 7Li 2-4‰) fluvial isotope ratios

Lithium in Seawater – 60 Ma

Seawater [Li] = 26 µM (?) δ7LiSW = 22‰ τ ≈ 1.2 Ma (?)

River Water δ7LiRiver ~ 3‰

[Li]River = 265 nM (?) δ7LiUCC = 1.7‰, [Li]UCC = 24 ppm

Silicate Reverse Weathering Low Temperature Basalt Alteration and

Sediment Diagenesis

δ7LiSediment = 6‰ δ7LiSediment = δ7LiSeawater - ∆SED

At Steady State; Li Input = Li Output

∆SW-SED = δSeawater - δSediment = 16‰

Subduction Refluxed Lithium

δ7LiReFlx = 6‰ δ7LiReFlx = δ7LiSediment

Hydrothermal Fluid δ7LiHT = 8.3‰

[Li]HT = 840 µM δ7Li�MORB = 3.7‰, [Li]MORB = 6 ppm

δ7Li Crash Across

K-Pg (KT) Boundary

• Across K-Pg (KT) boundary δ7LiSW dropped ~ 4 ‰ in < 0.7 Ma - Almost Impossible! - NOT bolide, NOT LIPs (Deccan Traps). Something important changed – what?

Interpretations

• Across K-Pg (KT) boundary δ7LiSW dropped ~ 4 ‰ in < 0.7 Ma -

Almost Impossible! - NOT bolide, NOT LIPs (Deccan Traps).

Something important changed – what?

Osmium Isotopes

6 stable isotopes: 184Os, 187Os, 188Os, 189Os, 190Os, and (most abundant) 192Os. The other natural isotope, 186Os, has an extremely long half-life (2×1015 years) and for practical purposes can be considered to be stable as well. 187Os is the daughter of 187Re (half-life 4.56×1010 years) and is most often measured in an 187Os/188Os ratio. Thus this is a radiogenic isotope system (like 87/86Sr).

184 185 186 187 188 189 190 191 192

Mass Number

Osmium IsotopeAbundances

1 9 0Pt 186OsHalf-life - 450 billion years

α

- 0.01%

Plat inum Isot opeAbundances

1 9 2 1 9 4 1 9 5 1 9 6 1 9 81 9 0

Mass Number

(Walker et al. 1997 )

Normalization • Early work reported 187Os/186Os • Now common convention is to report

187Os/188Os • This is what is actually measured most

commonly & 190Pt decay caused SUBTLE variation in 186Os abundance

• Rule of thumb: 187Os/188Os = 0.12 * 187Os/186Os

SOLID & LIQIUDCORE 99%

DEEP SILICATEEARTH 1%

EARTH'S CRUST0 .0 0 1 %

Most of the Earth's Os & Ir residein its core

Like Ir, Os is highly siderophile so...

strong Os enrichment and low 187Os/188Os in extraterrestrial material and mantle rocks compared to crustal rocks.

Re (ppb) Os (ppb) 187Re/188Os 187Os/188Os

Chondrites 40 500 0.42 0.127

Ultramafic Rocks 0.4 5 0.42 0.127

Old Crustal Rocks 0.5 .05 50 1.32

Seawater .008 .00001 4000 1.06

Organic-rich Sed. 30 0.2 800 1.06

Oxic pelagic clay 0.05 0.2 1.2 1.06

The Marine Osmium Isotope System

Sources and Sinks

The Marine Osmium System Reservoirs - Sources - Sinks

Extraterrestrial Impact and Deccan

Volcanism at the Cretaceous-Tertiary Boundary

Terminal Cretaceous Environmental Events Charles B. Officer & Charles L. Drake, Science 227, 8 March 1985, 1161-1166.

Original area: ~1 Million km2 (1.5% of land surface). Original volume: 2-4 Million km3. Effusion rate: ~10% of the average MORB production rate. Cover mostly Precambrian shield area.

Nickel-sulfide fire assay to pre-concentrate PGE

Advantages: Low blanks (e.g., 0.5 pg Os/g)

Large samples (up to 0.5 kg)

Robust chemistry

Fairly quick sample preparation

Does not require a clean lab

Suitable for most matrices

Os IC and [PGE] on same split

Disadvantages: High blank (e.g., 0.5 pg Os/g)

Not suitable for Re

Anomalously high platinum group element concentrations have previously been reported for Upper Triassic deep-sea sediments, which are interpreted to be derived from an extraterrestrial impact event. Os isotope data exhibit a marked negative excursion from an initial Os isotope ratio. This is synchronous with the ~215Ma Manicouagan impact event.

Conclusions The main phase of Deccan volcanism predates the K/T boundary impact.

The ~10 kyr residence time of Os in seawater decreases the likelihood of missing a large impact signal due to an incomplete sediment record.

The seawater record of Os recovers quickly (<100 kyr) from the impact event.

Diesel Use and Os Isotopes

Particles

Road

dust

Soil

Automobile

Runoff

Sediments

This image cannot currently be displayed.

River water

Environmental Pathways

Peat bog

Greenland ice

Upper Mystic Lake, N. Boston

Coring location Depth 25 meter

Aberjona Watershed - residential area 76,000 inhab. - industrial area (Superfund site) 65,000 cars per day, major roads (I93, I95)

Sediment cores 2 cm sections

Dried 105oC

Dated (210Pb, laminations, As and Cr)

MW digestion Q-ICP-MS

Isotopic dilution NiS fire assay

HR-ICP-MS

Pt concentration profile Upper Mystic Lake, MA

0

10

20

3040

50

60

70

1880 1900 1920 1940 1960 1980 2000Calendar Year

Pt C

once

ntra

tion

(ng

g-1

)

Core 1 Core 2Core 3 Core 4Core 1

ES&T 2003, 37, 3283 and ES&T 2004, 38, 396

0.00.10.20.30.40.50.60.70.80.91.0

1880 1900 1920 1940 1960 1980 2000

Calendar Year

Pt C

once

ntra

tion

(ng

g-1)

Pt concentrations in Greenland ice

Introduction of catalytic converters

8000BP 6000BP

Barbante et al. (2001) ES&T 35, 835-839

Summary

• Catalytic converters are important sources of PGE to the environment.

• Anthropogenic PGE are regionally dispersed.

• Distal dispersal (i.e., Greenland ice) seems to require fractionation of PGE during transport.

• Alternatively, observed enrichment in Greenland ice is caused by other industrial sources (smelters) or natural sources (dust, volcanic aerosols).

Anthropogenic osmium in rain and snow reveals global-scale atmospheric contamination. Chen et al., 2008

The 187Os/188Os ratios of these samples are relatively low (0.16–0.48), and fall along a 2-component mixing line natural & anthropogenic