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Lithium Isotopes Standard: NIST L-SVEC Li (SRM 8545) 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 Tracing weathering processes Schematic illustration of Li isotope systematics in the hydrological cycle, modified from Elliott et al. (2004). Tracing crust/mantle recycling Schematic illustration of Li isotope systematics in a subductionzone 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 Uplift Erosion Weathering CO2 Drawdown Cooling Subduction Volcanism Elevated CO2 Warming CO2 H2O Weathering Continental Run Off Ca2+ + Si(OH)4 Continental Plate Ca2+ + 2HCO3- → CaCO3 + CO2 + H2O CO2 H2O Sedimentation Subduction CaCO3 + SiO2 ↔ CaSiO3 + CO2 Si(OH)4 → SiO2 + 2H2O Sedimentation MOR Post-Urey: HT Fluxes & Low Temp. Authigenic Aluminosilicate Formation: “Reverse Weathering” Cations+Al+Si 2o-Clays Cenozoic Climate: CO2 and weathering feedbacks Zachos et al., 2001 Benthic Foraminifera Seawater Strontium Isotopes 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. Himalayan Orogeny Urey’s Tectonic Cycle - Where does Li fit in? Accepted Value 31.0 ‰ ± 0.5 ‰ Contrast: Almost all igneous rocks on Earth are between 0 and 4‰, so seawater Li is very heavy FLi in 109 Moles/yr Weathering Lithium Geochemistry is Lithophilic Lithium cycle is virtually all in silicate rocks and aluminosilicate clays – none in carbonates CO2 H2O Continental Run Off FRiver = 10 δ7LiRiver = 23‰ [Li]UCC= 24 ppm δ7LiUCC=1.7‰ [Li]Silicate >> [Li]Carbonate Li → 2º Clays Authigenic Clay Formation And Low temperature δ7LiHT= 8.3‰ FReFlx= 6 Basalt Alteration δ7LiReFlx= 15‰ FHT= 13 Subduction MOR [Li]MORB= 6 ppm δ7LiMORB=3.4‰ 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 River Water At Steady State; Li Input = Li Output δ7LiRiver = 23‰ [Li]River = 265 nM δ7LiUCC = 1.7‰, [Li]UCC = 24 ppm Seawater [Li] = 26 µM δ7LiSW = 31‰ τ ≈ 1.2 Ma Hydrothermal Fluid δ7LiHT = 8.3‰ [Li]HT = 840 µM δ7Li MORB = 3.7‰, [Li]MORB = 6 ppm ∆SW-SED = δSeawater - δSediment = 16‰ Subduction Refluxed Lithium δ7LiReFlx = 15‰ δ7LiReFlx = δ7LiSediment Silicate Reverse Weathering Low Temperature Basalt Alteration and Sediment Diagenesis δ7LiSediment = 15‰ δ7LiSediment = δ7LiSeawater - ∆SED Planktonic Forams & Bulk Forams Orbulina universa N. dutertrei Globigerina venezuelana Globigerina cryptomphala Globigerina eocaena Globigerina inequispira spp Marginotruncana spp. Hedbergella spp G. truncatulinoides G. triloba 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 Globigerina triloba Li/Ca & δ7Li of Core-top & Tow Forams Misra & Froelich, JAAS, 2009 [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 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 18 δ O 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 UreyWalker-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 Pogge et al., 2013 lightest values of the Li isotope ratio (7Li) during OAE2, indicating high levels of weathering—and therefore atmospheric CO2 removal. 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 River Water At Steady State; Li Input = Li Output δ7LiRiver ~ 3‰ [Li]River = 265 nM (?) δ7LiUCC = 1.7‰, [Li]UCC = 24 ppm ∆SW-SED = δSeawater - δSediment = 16‰ Seawater [Li] = 26 µM (?) δ7LiSW = 22‰ τ ≈ 1.2 Ma (?) Hydrothermal Fluid δ7Li = 8.3‰ [Li]HT = 840 µM δ7Li MORB = 3.7‰, [Li]MORB = 6 ppm HT Subduction Refluxed Lithium δ7LiReFlx = 6‰ δ7LiReFlx = δ7LiSediment Silicate Reverse Weathering Low Temperature Basalt Alteration and Sediment Diagenesis δ7LiSediment = 6‰ δ7LiSediment = δ7LiSeawater - ∆SED 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, Something important changed – what? NOT LIPs (Deccan Traps). 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). 190 α 18 6 Pt Half-life 450 ( Walker et Os billion years al. 1 9 9 7 ) Plat inum Isot ope Abundances 0.01% 190 192 194 195 196 Mass Number Osmium Isot ope Abundances 184 185 186 187 188 189 Mass Number 190 191 192 198 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 Like Ir, Os is highly siderophile so... Most of t he Eart h's Os & Ir reside in it s core EARTH'S CRUST SOLID & LIQIUD 0 .0 0 1 % CORE 9 9 % DEEP SILICATE EARTH 1 % 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 System The Marine Osmium Isotope Reservoirs - Sources - Sinks System Sources and 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 Environmental Pathways Automobile This image cannot currently be displayed. Particle s Greenland ice Peat bog Soil Roa d dust Runof f River water Sediments Upper Mystic Lake, N. Boston Aberjona Watershed - residential area 76,000 inhab. - industrial area (Superfund site) 65,000 cars per day, major roads (I93, I95) Coring location Depth 25 meter 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 (ng g -1) Pt concentration profile Upper Mystic Lake, MA 70 60 Core 1 Core 2 50 Core 3 Core 4 40 Core 1 30 20 10 0 1880 1900 1920 1940 1960 Calendar Year ES&T 2003, 37, 3283 and ES&T 2004, 38, 396 1980 2000 Pt Concentration (ng g -1 ) Pt concentrations in Greenland ice 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 1880 Introduction of catalytic converters 1900 1920 1940 1960 8000BP 6000BP Calendar Year Barbante et al. (2001) ES&T 35, 835839 1980 2000 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). The 187Os/188Os ratios of these samples are relatively low (0.16–0.48), and fall along a 2-component mixing line natural & anthropogenic Anthropogenic osmium in rain and snow reveals global-scale atmospheric contamination. Chen et al., 2008