An organic geochemist s perspective on the (radio)carbon cycle

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1 An organic geochemist s perspective on the (radio)carbon cycle Suggested General Reading: McNichol A.P. and Aluwihare L.I. (27) The Power of Radiocarbon in Biogeochemical Studies of the Marine Carbon Cycle: Insights from Studies of Dissolved and Particulate Organic Carbon (DOC and POC). Chem. Rev. 17, Ingalls A.E. & Pearson A. (25) Ten years of compound specific radiocarbon analysis. Oceanography magazine Eglinton, T.I. and Repeta, D.J. (23). Organic Matter in the Contemporary Ocean. In: Treatise On Geochemistry (K. Turekian and H. Holland, eds.) Elsevier, London. pp Format of Lecture Radiocarbon systematics. C variations in bulk organic matter pools. Compound specific radiocarbon analysis. 1

2 The Global Organic Carbon Cycle ATMOSPHERIC CO 2 (75) SEDIMENTARY ROCKS (KEROGEN) (15,,) LAND PLANTS (57) terrestrial primary production physical weathering humification river or eolian transport marine primary production uplift SOILS (1,6) OCEAN BIOTA (3) POC (2) OC burial DOC (68) (units=1 15 gc) Modified after Hedges (1992) Sizes of boxes are not to scale burial MODERN OCEAN SEDIMENTS (1) C age of bulk organic carbon in surface marine sediments C age (yr) Water Depth (m) river-dominated shelf abyssal anoxic shelf basin OMZ open shelf continental slope 6 7 2

A brief introduction to radiocarbon C is a cosmogenic nuclide - continually formed in the upper atmosphere by interaction of neutrons (produced by cosmic rays) and nitrogen atoms.

Natural isotope abundances (contemporary sample): 12 C - 99% 13 C - 1% C - 1 part per trillion (1-12 ) There is a dynamic equilibrium between C formation and decay, leading to an approximately

3 A brief introduction to radiocarbon C is a cosmogenic nuclide - continually formed in the upper atmosphere by interaction of neutrons (produced by cosmic rays) and nitrogen atoms. N + neutron C + proton C atoms rapidly combine with oxygen to form CO 2 which mixes throughout atmosphere, dissolves in the oceans, and enters the biosphere via photosynthetic carbon fixation. Natural isotope abundances (contemporary sample): 12 C - 99% 13 C - 1% C - 1 part per trillion (1-12 ) There is a dynamic equilibrium between C formation and decay, leading to an approximately constant level in the atmosphere. Current estimated half-life, T½, of C = 573 yr Key attribute: Half life of C is suitable for studying processes and dating carbonaceous materials over yr time-scales ideal for carbon cycle studies. 3

4 Radiocarbon Systematics and Conventions Conventional (Libby) half-life adopted for reporting C ages = 5568 yr (3% smaller than true half-life of 573 yr). The half-life is related to the meanlife,τ, by: T½ = (ln2)τ (or T½ =.693τ) Corresponding meanlife, τ, for Libby halflife is 833yr. The radiocarbon age ( C yr), t, can be determined from: t = -τ ln(a/a ) (or t = -833 ln(a/a )) where A is the number of atoms (activity) after time t and A is the initial number of atoms/activity. NB. Important distinction: radiocarbon age versus calibrated radiocarbon age Radiocarbon systematics The absolute international standard of C activity (A abs ) is defined as 95% of the C activity of the original oxalic acid standard (HOxI), in the year 195. This is equivalent to the activity of 19 th century (189 AD) wood. This value represents the C concentration of the atmosphere prior to anthropogenic influence (fossil fuel combustion, atomic weapons testing). 4

5 Radiocarbon systematics The measured activity of HOxI (A ox ) is corrected for fractionation effects using a defined δ 13 C ox value of 19 to yield the fractionation-normalized activity (A ON ): A ON =.95A ox ( δ 13 C) This is corrected to account for radioactive decay between 195 and the year of measurement (y): A abs = A ON e λ ( y 195) Radiocarbon systematics The measured C activity of a sample (A s ) is normalized (A sn ) to a constant δ 13 C value of 25 to remove the influence of isotopic fractionation on the reported concentration: A sn = 13 2(25 + δ C A s 1 1 sample ) To a first approximation, the above equation treats the C fractionation as twice the 13 C fractionation (to account for the greater mass difference). This is based on physical-chemical derivations that suggest the C fractionation is approximately equal to the square of the 13 C fractionation. The mean age correction is about 16 years for every 1 difference from

6 Radiocarbon systematics Conventions for radiocarbon systematics were first established based on activities determined from measurements of radioactive decay (from decay counting techniques). Natural abundances of radiocarbon are now more commonly measured by Accelerator Mass Spectrometry (AMS). AMS yields absolute ratios of C/ 12 C (or C/ 13 C) in a sample, rather than the rate of decay (activity). The above equations are still applicable, as activity and R /12 are proportional via the decay constant, λ (based on the real half-life = ). AMS data are reported as fraction modern (f m ) values, rather than activities: f m = pmc A A sn.1( ) = = ON R R sn ON C systematics In classical radiocarbon dating applications, the calculated radiocarbon ages are converted to calendar ages using calibration curves. When a radiocarbon age (year date) is not desired, data are often reported as Δ C values in one of two forms: For samples with no age correction, where y is the year of measurement: Δ Δ C = C = λ ( y 195) ( f m e 1) * 1 For samples of known geochronological age, where y is the year of measurement, and x is the year of sample formation: ( f e λ (195 x) m 1) * 1 Δ C originally defined by Broecker and Olson (1959). Am. J. Sci. Radiocarbon Suppl. 1,

7 Conventions Age Ct = Ce λt Δ C t = 833ln 1+ 1 Isotope Ratio R δ C = 1 1 RStd 13 δ C Δ C = δ C 2( δ C + 25) 1+ 1 Isotope fractionation effects are deliberately removed! δ C ( ) δ 13 C( ) Δ C ( ) δ 13 C ( ) (1) (2) Age Ct = Ce λt Δ C t = 833ln 1+ 1 Conventions Isotope Ratio R δ C = 1 1 RStd 13 δ C Δ C = C δ ( δ C ) (3) (4) 6 Δ C is useful for isotopic mass balance calculations Radiocarbon Age Radiocarbon Age ± 5 t1/ Δ Δ C ( ) ( ) 57, years Δ C Age 573 years years 7

8 Reporting of Radiocarbon Data 1 1. Percent Modern Carbon (pmc) Fraction Modern (F m ) Δ C (permil) C age (yr BP) Fm and pmc report the fractional amount of C in a sample relative to that in the standard. - A radiocarbon age ( C yr), is not a calendar or chronological age and must be calibrated. - Δ C normalizes the C content of a sample to the same δ 13 C (-25 permil) and time-point (195 AD). It is a linear quantity & can be used in mass balances. Factors controlling isotopic contents 13 C C (1) The carbon source utilized (2) Isotope effect of assimilation (3) Isotope effect of biosynthesis (4) Cellular carbon budget (5) n/a (6) Heterogeneity of sources (1) The carbon source utilized (2) n/a (3) n/a (4) n/a (5) Time (6) Heterogeneity of sources 8

9 Methods of C measurement Conventional method: Determination of C activity of a weighed sample by counting the number of electrons (beta particles) emitted from nucleus per unit time by the decay of C. Beta-counting can be performed by samples combusted to CO 2 (gas proportional beta counting) or on samples converted to benzene and measured photometrically after addition of a scintillator (liquid scintillation counting). Sample size requirements: > 1 g C and long counting times (days). Methods of C measurement Accelerator Mass Spectrometry (AMS) Direct measurement of the proportion of C atoms (versus 13 C or 12 C). Measurements are typically made on graphite (CO 2 also possible). Graphite is formed by combustion of sample to CO 2 and then reduction of CO 2. Measurement times ~ 2 min (preparation time ~ 3 days). Key attribute of AMS - Isobar rejection: Negative ions (Cs sputter source) remove ( N + ) Electron stripping (accelerator) to remove hydrides ( 13 CH - ) Sensitivity of AMS = ( 6, yr; 1 half-lives). Sample size requirements: Standard targets < 1 milligram C (as little as 3 μg C) for full precision (+/- 4 ) As low as 5 μg C now possible at reduced precision (+/ ). Blanks become major issue at these low sample sizes. Standards: Oxalic acid (HOxI, HOxII) 9

10 Accelerator Mass Spectrometer Factors influencing radiocarbon abundances: 1. Atmospheric C variations Variations in solar (cosmic ray flux) activity (long-term, ~ 1 3 yr variations in production rate). Variations in Earth s geomagnetic field strength (short-term, < 1 2 yr variation in production rate) Climate induced variations - solubility of CO 2 in water a function of temperature. Volcanic activity (outgassing of CO 2 ) Anthropogenic activity. - Fossil fuel burning ( Suess effect ). - Nuclear weapons testing ( Bomb spike ). 1

11 Factors influencing radiocarbon abundances: 2. Source or reservoir effects. There is rapid global mixing between the atmosphere and the terrestrial biosphere. However, mixing rates in deep ocean are slow. Mixing between surface mixed layer (high C) and deeper layers (lower C) gives rise to an offset between mixed layer and atmosphere. This offset ( reservoir effect ) for the pre-bomb era is on average ca. 4 yr, but varies spatially and temporally. Thus organic matter synthesized in the oceans will have an apparent age which is 4 yr older than terrestrial biomass synthesized at the same time. C variations and radiocarbon calibration Cosmic ray flux variations Geomagnetic field variations High precision C calibration curve for the past 7 yr (from Irish Oak tree ring chronology). Straight line is the 1:1 correspondence between C age and dendrochronological age. Short-term (1 2 yr) variations are due to geomagnetic field variations. Long-term (1 3 yr) variations are due to variations in cosmic ray flux. 11

Radiocarbon dating: Wiggle-matching, dendrochronologies and varve chronologies In classical radiocarbon dating applications, the calculated radiocarbon ages are converted to calendar ages using

12 Radiocarbon dating: Wiggle-matching, dendrochronologies and varve chronologies In classical radiocarbon dating applications, the calculated radiocarbon ages are converted to calendar ages using calibration curves. C variations vs varve age for Cariaco basin sediments, compared to those from tree rings Cariaco Basin Hughen et al., 1998 Nature, v391 Radiocarbon calibration Tree-rings Δ C in the atmosphere as a function of calendar year. Data obtained from INTCAL4 12

Potential limitations in assigning Calendar ages from C data Two possible dates Dating uncertainty Accurate date Recent variations of C in atmospheric CO 2

13 Potential limitations in assigning Calendar ages from C data Two possible dates Dating uncertainty Accurate date Recent variations of C in atmospheric CO Fraction modern (f M ) Maunder Minimum The Bomb Spike Δ C ( ) 1 The Suess Effect? Calender Year 2 13

14 The bomb spike in the atmosphere and surface ocean

15 Radiocarbon Distribution CO 2 Land Biosphere Mixed-Layer DIC Mixed-Layer DOC Photoautotrophs Deep Ocean DIC Particulate Organic Detritus Heterotrophs Surface Sediments Chemoautotrophs Heterotrophs Deep Ocean DOC L. Aluwihare; modified from Pearson, 2 15

16 How does radiocarbon vary between different carbon pools in the marine environment? A few examples for marine sediments: C variations as a function of water depth (see above). C variations as a function of sediment depth. C variations as a function of grain size. C variations as a chemical class. C variations at the molecular level. Variations in C age of organic matter as a function of sediment depth C age (yr BP) Depth (cm) (Benoit et al., 1979) Radiocarbon age of bulk OC in Long Island Sound sediments 16

Influence of hydrodynamic particle sorting on radiocarbon ages (Washington

sediment grain size Washington Margin Cascadia Basin transect Coppola et al.

1-63 63-38 Grain size (μm) Corg <38 <38 >1m d-1 <38 <1m d-1 3 25 2 15 1 3 25

17 Influence of hydrodynamic particle sorting on radiocarbon ages (Washington margin) Washington Margin (Columbia R) C variations in as a function of sediment grain size Washington Margin Cascadia Basin transect Coppola et al. 27. Organic carbon (%) 3 WM C/N 4 WM4 Bulk Bulk-vapor > Grain size (μm) Corg <38 <38 >1m d-1 <38 <1m d Corg/Ntot δ 13 Corg (permil) -21 WM WM Grain s Uchida et al., in prep. δ 13 C Δ C Bulk Bulk-vapor > <38 <38 >1m d-1 <38 <1m d Grain s Grain size (μm) Δ Corg (permil) 17

$We are only isotopically characterizing a small fraction of the OC in the marine environment at the molecular level Variations in 13 C and C composition of organic matter as a function of chemical$

18 We are only isotopically characterizing a small fraction of the OC in the marine environment at the molecular level Variations in 13 C and C composition of organic matter as a function of chemical compound class Height above bottom (m) TOC THAA TCHO Lipid Acid-insol BC alkenone aggregates flocc plankton zooplankton sinking POM Depth in sediment (cm) Station M Wang, Druffel et al. a δ 13 C ( ) Δ C ( ) b 18

19 Compound Specific Radiocarbon Analysis (CSRA) Molecular level C measurements are required to understand C variations in bulk organic pools. The Challenge: To measure the natural abundance of C in individual organic compounds in complex environmental mixtures. Greater than 25 μg C required for reliable C measurement (by AMS). Isolation of target analytes in very high purity. Conventional capillary GC resolves < 5ng compound. Approaches: Automated Preparative Capillary Gas Chromatography (PCGC). Preparative LC Wet chemical purification methods Generalized purification scheme for CSRA 19

Compound-Specific Radiocarbon Analysis: Present Status Ingalls & Pearson, 25 Molecular C case studies Suggested Reading: N. Ohkouchi et al 22 Science 298 1224-1227. A. Pearson et al 2 Paleoceanog 15 541-55.

20 Compound-Specific Radiocarbon Analysis: Present Status Ingalls & Pearson, 25 Molecular C case studies Suggested Reading: N. Ohkouchi et al 22 Science A. Pearson et al 2 Paleoceanog G. Mollenhauer & T. Eglinton 27 L&O R. Smittenberg et al 26 Science N. Drenzek et al 27 Mar Chem G. Slater et al 25 ES&T A. Ingalls et al 26 PNAS S. Petsch et al 21 Science S. Shah et al 28 GCA 72,

21 CSRA selected topics Particulate organic matter dynamics in the marine environment The transfer of terrestrial organic matter transfer to the oceans Other case studies Particulate organic matter dynamics in the marine environment Development of sediment chronologies. Influence of hydrodynamic processes Dispersal of terrestrial organic matter over continental margins. Evidence for lateral particle transport Margin-to-deep ocean transport of organic matter. 21

6 Benthic forams Post-Bomb interval DIC TOC Planktonic forams Pre-Bomb interval 1996 1985 1961 1937 1913 1899 Δ C 15 1 5-5 -1-15 -2

22 California Borderland Basins California Borderland Basins - Anoxic laminated sediments - High sedimentation rates Phytoplankton sterols as tracers of surface ocean DI C Santa Monica Basin sediments Depth in sediment core z (cm) Δ C Benthic forams Post-Bomb interval DIC TOC Planktonic forams Pre-Bomb interval Δ C ± ± 19 SMB, TOC SMB, TOC Postbomb DIC SMB -1 SBB -1 SMB 5-6 Prebomb DIC δ 13 C Data from Pearson et al. (2) 22

Developing sediment chronologies for the Ross Sea, Antarctica Ross Sea Surface Sedimentary OC composition Site Fairy Water Depth (m) 671 TOC (%).24 δ 13 C -25.65 C age 999 Gentoo 623.34-27.

23 Developing sediment chronologies for the Ross Sea, Antarctica Ross Sea Surface Sedimentary OC composition Site Fairy Water Depth (m) 671 TOC (%).24 δ 13 C C age 999 Gentoo Emperor Chinstrap Ross Sea - Paucity of forams - Old OC in core-top sediments Antarctica Data source: Ohkouchi et al. (23) Fatty acid vs TOC C ages of Ross Sea sediments Chinstrap Site C fatty acid C16 fatty acid C18 fatty acid TOC Data source: Ohkouchi et al. (23) Depth in core (cm) cm/kyr Post-bomb DIC 7.5 cm/kyr Pre-bomb DIC Calendar year (yr BP) (OxCal3 calibration) 23

Molecular Sedimentology Coupled molecular and

both encode surface ocean-derived signatures

Age discrepancies must therefore indicate

$associated with the fine fraction of sediments$ prone to resuspension and redistribution.

particles less susceptible to redistribution by

Huxleyi C37 alkenone The Bermuda Rise Atlantic

A deep ocean (~ 45m water depth) sediment drift.

24 Molecular Sedimentology Coupled molecular and microfossil C analysis Premise: Marine algal biomarker compounds (e.g., alkenones, sterols) and planktonic forams both encode surface ocean-derived signatures (incl. C content of DIC). Age discrepancies must therefore indicate different subsequent fates. Marine organic matter is predominantly associated with the fine fraction of sediments prone to resuspension and redistribution. Foraminiferal tests are coarse, sand-sized particles less susceptible to redistribution by bottom currents. G. ruber E. Huxleyi C37 alkenone The Bermuda Rise Atlantic Ocean Located northeast of Bermuda. A deep ocean (~ 45m water depth) sediment drift. Unusually high sediment accumulation rates. Bermuda Island Subject of numerous paleoceanographic studies. Sediment box core studied using molecular carbon- methods. 24

Geochemical Records from the Bermuda Rise

25 Geochemical Records from the Bermuda Rise Age difference (vs planktonic forams) %CaCO U K ' 37 alkenones TOC 5 FFIC 5 5 Age (Calendar years) Ohkouchi et al. 22 Primary productivity and SST in the NW Atlantic Ocean Nova Scotia Cape Cod Bermuda 25

26 A mechanism for long-range transport of organic matter (and alkenones) from the Scotian Margin to the Bermuda Rise? Influence of hydrodynamic particle sorting on radiocarbon ages (Washington margin) Columbia River Upper slope WM4 Outer shelf (WM3) 26

27 Radiocarbon ages of individual fatty acids in size-fractionated sediments WM3 WM4 Terrestrial (long-chain) fatty acids older in Outer shelf Upper slope slope than shelf surface sediments - Aging during lateral transport? Terrestrial fatty acid age increases with increasing grain-size -More rapid nepheloid layer transport of fine particles? Aging during transport? Can C measurements on vascular plant markers yield information on timescales of across-margin transport of sedimentary particles? Grain size Uchida et al., unpublished results Timescales of terrestrial organic matter transfer to the oceans Global variations on terrestrial organic carbon residence times in river drainage basins. A closer look at residence times: tracing the bomb spike from source to sink. 27

28 Timescales of terrestrial carbon export Δt Δ C of suspended POC from world rivers Data include Brahmaputra (circles), Ganges (squares), lower Meghna (triangles), Yangtze (hexagons) rivers. A Δ C value of > indicates the presence of bomb C. Data compiled by A. Dickens and V. Galy. 28

29 plant wax lipids Bulk vs molecularlevel C analysis of riverine particulate organic matter 5 C24 n-acid Ob-1 Ob-2 Mackenzie C26 n-acid C28 n-acid C3 n-acid 1 Ob-1 bulk C age (years b.p.) Riverine 1 & 2 prodn Ob-2 bulk Fossil (kerogen) OC Mackenzie bulk 12 C24 n-acid C26 n-acid C28 n-acid C3 n-acid Molecular multi-isotopic studies of riverine organic matter Mackenzie Ob Cowichan (Saanich) Columbia Eel Pettaquamscutt Danube Mississippi Unare (Cariaco) Beni Congo Waiapu 29

30 Latitudinal control on terrestrial biomarker residence times? 1 Δ C (permil) C age (yr BP) ave n-acids (C24+) ave n-alcohols (C24+) ave n-alkanes (C25+) ave lignin phenols Latitude N/S A closer look at terrestrial OC residence times 12W 6W Saanich Inlet 2N Saanich Inlet 'W 'W 68W Cariaco Basin 64W 11N 4N 4N Cariaco Basin 2N 12W 6W 1 m 11N 48 36'N 48 36'N Rio Tuy 1 m 5 m Rio Unare 48 24'N km 'W 48 24'N 'W 9N km W 64W 9N 3

Δ C Saanich Inlet core 137 Cs 2 Lignin 1963 1957 Varve Counting Varve Counting 199 21 Pb 198 197 196 195 194 TOC Plant Waxes Atmospheric CO 2 Bomb spike Conceptual Framework Terrestrial Organic

31 Δ C Saanich Inlet core 137 Cs 2 Lignin Varve Counting Varve Counting Pb TOC Plant Waxes Atmospheric CO 2 Bomb spike Conceptual Framework Terrestrial Organic Matter Supply to Saanich Inlet, British Columbia, CA Model results indicate that 8% of plant wax signal derives from a ~ 5 yr-old (soil) carbon reservoir See also Smittenberg et al 26 Science 31

Fractions Black Carbon Carbon isotopic composition of dustfall sample off NW Africa Organic Carbon

32 Soil OC build-up and erosion has not reached steady state in the time since deglaciation. Plant wax n-alkanes, PCGC Transport can be rapid, but carbon can be old! Fractions Black Carbon Carbon isotopic composition of dustfall sample off NW Africa Organic Carbon Plant wax alcohols Abundance 1.2 %.24 % 12 μg/gdw δ 13 C ( ) Δ C ( ) C age (yr BP) 126 ± 4 27 ± ± 3 32

33 C age variability in Bermuda Rise surface (-3 cm) sediment Δ C (permil) G. ruber G. inflata Tracer of DIC C in overlying surface waters planktonic forams Labile algal biomarkers total (minor organic advected carbon component?) 1 alkenones fatty acids 2 hydrocarbons 3 Refractory algal Pre-aged biomarkers refractory (large plant advected waxes component) 4 (advected + eolian component)? 5 TOC (-1cm) TOC (1-2cm) Alkenones (-1cm) Alkenones (1-2cm) C16 fatty acid C18 fatty acid C24 fatty acid C26 fatty acid C28 fatty acid Bulk OC = advected marine OM? C21+C23+C25 alkanes C22+C24+C26 alkanes C27 alkane C29+C31 alkanes C28+C3+C32 alkanes UCM C age (yr BP) Petrogenic hydrocarbons (fossil inputs) Ohkouchi et al., submitted Some additional applications of compound-specific radiocarbon analysis Constraining microbial carbon sources Determining sources of compounds of unknown origin. Apportioning sources of polycyclic aromatic hydrocarbons in the environment. 33

Compound Specific Radiocarbon Analysis Examples: Constraining metabolism of microbial communities Planktonic Archaea Bacteria on oceanic

34 Compound Specific Radiocarbon Analysis Examples: Constraining metabolism of microbial communities Planktonic Archaea Bacteria on oceanic suspended particles Petroleum degradation Kerogen degradation Establishing the origin of compounds of environmental concern. Halogenated OCs PAHs 34

Constraining metabolism of microbial communities planktonic archaea Direct evidence for autotrophic C-uptake by planktonic archaea Pearson et al 21

35 Constraining metabolism of microbial communities planktonic archaea Direct evidence for autotrophic C-uptake by planktonic archaea Pearson et al 21 GCA Mass balance at 67m: GDGTs are % sinking, 15% heterotrophy, 71% autotrophy. HO O O O O OH Archaeal GDGTs, HPLC Könneke et al., 25 35

Carbon sources for heterotrophic bacteria in oligotrophic surface and deep waters Δ C and δ 13 C values are nearly identical between surface and deep samples.

36 Carbon sources for heterotrophic bacteria in oligotrophic surface and deep waters Δ C and δ 13 C values are nearly identical between surface and deep samples. Fatty Acids, PCGC O OH Δ C ( ) Water Column Fatty Acids - NCP (POC <.5μm) DeepPLFAs Surface PLFAs Deep Surface Relative Abundance, PLFAs δ 13 C ( ) Close, Shah, Pearson et al., (27) Modern carbon supports suspended bacteria in the oligotrophic ocean. (In prep.).5 C12 C: C16:1 C16: C17:1 C17: C18:1 C18: Assessing microbial response to petroleum residues in salt marsh sediments No uptake of petroleum C into bacterial PLFAs in an old, degraded oil spill. O Fatty Acids, PCGC OH Contaminated horizon No evidence of C-depleted Microbial lipids in contaminated interval 36

Fatty Acids, PCGC O OH Microbial consumption of fossil carbon (kerogen) during weathering

37 Bacterial uptake of hydrothermal petroleum in Guaymas Basin sediments Significant petroleum C in bacterial PLFAs above zone of active oil production. Fatty Acids, PCGC O OH Microbial consumption of fossil carbon (kerogen) during weathering of organic-rich sedimentary rocks Nearly 1% of carbon in bacterial PLFAs derived from shale kerogen. Fatty Acids, PCGC O OH 37

38 PBBs accumulate in marine mammals; source is natural, maybe sponges/bacteria. MeO-PBDEs, PCGC Methoxylated polybrominated diphenyl ethers 38

Geochemistry of Radiocarbon in Organic Materials

Geochemistry of Radiocarbon in Organic Materials Suggested Reading: Eglinton T.I., Benitez-Nelson B.C., Pearson A., McNichol A.P., Bauer J.E. and Druffel E.R.M. (1997) Variability in radiocarbon ages of