Old carbon in the modern marine environment

Transcription

1 Old carbon in the modern marine environment Possible origin(s) of non-zero 14 C ages for OC carbon in marine surface sediments: 1. Delivery of pre-aged terrestrial OC of vascular plant origin 2. Relict OC ( kerogen ) inputs from erosion of sedimentary rocks 3. Sediment redistribution processes - Bioturbation - Lateral advection 4. Black Carbon The Global Organic Carbon Cycle (ca. 195) ATMOSPHERIC CO 2 (75) fossil fuel utilization SEDIMENTARY ROCKS (KEROGEN) (15,,) -2 to -35 t = infinite uplift physical weathering (.2) LAND PLANTS (57) -25 to -3 (C3) -14 to -2 (C4) t = yr humification (5) SOIL HUMUS (1,6) -25 to -3 (C3) -14 to -2 (C4) t =1-1, yr net terrestrial primary production (5) river or eolian transport (POC=.15) OC preservation (.15) net marine primary production (5) OCEAN (BIOTA) (3) -2 to -3 (C3) t = 4 yr sediment redistribution (units=1 15 gc) Modified after Hedges (1992) burial RECENT SEDIMENTS (1) -2 to -25 t =?? yr

2 TOC and foraminiferal 14 C in Santa Monica Basin sediments 14 C DIC 2 TOC 1985 z (cm) 3 4 Planktonic forams Benthic forams C contents of algal sterols in CBB sediments 15 1 Post-bomb DIC ± C ± 19 SMB, TOC SMB -1 SBB -1 SMB Pre-bomb DIC -15 SMB, TOC δ 13 C Data from Pearson et al. (2)

3 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 Antarctica Data source: Ohkouchi et al. (23) Fatty acid and TOC 14 C chronologies for Ross Sea sediments Chinstrap Site C14 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)

4 Coupled molecular and microfossil 14 C measurements Premise: Marine algal biomarker compounds (e.g., alkenones) and planktonic forams both encode surface ocean-derived signatures (incl. 14 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. Approach: Use 14 C relationships between planktonic foraminifera, algal biomarkers (e.g., alkenones), and bulk OC isolated from the same sediment intervals as a tool to examine sedimentological processes (lateral transport, bioturbation). C 37 alkenone E. Huxleyi Sedimentological Controls on 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

5 Nova Scotia Cape Cod Bermuda SeaWiFS satellite image of E. huxleyi bloom off Newfoundland in the western Atlantic on 21st July, 1999.

6 ? Long-range transport of organic matter (and alkenones) from the Scotian Margin to the Bermuda Rise? Lateral transport of organic matter to the Bermuda Rise?

7 Lateral transport of organic matter to the Bermuda Rise? Sources and Transport of Alkenones and Forams to the Bermuda Rise PRESENT DAY COLD SST TERRIGENOUS SEDIMENT COLD ALKENONES SARGASSO SEA WARM SST PLANKTONIC FORAMS WARM CaCO 3 ALKENONES SCOTIAN MARGIN LAURENTIAN FAN PARTICLE RESUSPENSION ADVECTION OF OLD, COLD ALKENONES ON CLAYS/SILTS FOCUSSING BERMUDA RISE N LITTLE ICE AGE TERRIGENOUS SEDIMENT SCOTIAN MARGIN COLD SST LAURENTIAN FAN COLD ALKENONES PARTICLE RESUSPENSION N SARGASSO SEA ADVECTION OF OLD, COLD ALKENONES ON CLAYS/SILTS WARM SST PLANKTONIC FORAMS WARM CaCO 3 ALKENONES FOCUSSING BERMUDA RISE

8 Science goes in circles! HEBBLE Study area Namibian margin (Benguela Upwelling region) -2 cm alkenones and bulk OC modern age 2-12 cm (pre-bomb) alkenones: 118 yrs ~ Reservoir age Namibia 1-1 cm alkenones 25 yr bulk OC 227 yr foraminifera 25 yr Elevation (m) -55 Data from Mollenhauer et al., 23

9 14 C ages of Namibian margin sedimentary components (core ) Total organic carbon Total organic carbon Depth (cm) 8 1 Alkenones Alkenones Plantonic forams ( G. bulloides) C age (yr) 14 C age difference vs forams (yr) Mollenhauer et al., 23 Accumulation maximum (depocenter) on upper continental slope a) 1 N S Walvis Bay Lüderitz TOC (%) Water Depth [m] (Vp=15 m/s) Distance [km] b) erosion? increased accumulation 2 m Sites of increased accumulation in protected locations (depocenters): Implication of current controlled sedimentation Seismic data processing: André Janke Mollenhauer et al., 22

10 Mollenhauer et al. In press. Chile Conventional 14 C age (yr BP) 14 C age (yr) Southern Chile GeoB Chile bulk OC alkenones planktic foraminifera bulk OC - forams 2 1 alkenones - forams Core depth (cm) 14 C age discrepancies between organic matter and calcareous microfossils Age difference ( 14 C years) Closed symbols = Alkenone-foram age discrepancy Open symbols = TOC-foram age discrepancy Bermuda Rise Namibian Slope Chilean Margin NW African Slope Santa Barbara Basin Namibian Shelf Scotian Shelf (Emerald Basin) New England Shelf (Mud Patch) Gulf of Mexico Oman Margin Indian Ocean Sample Eglinton et al. unpublished

11 Estimates of advective alkenone contributions Assumptions: 14 C of indigenous alkenones = 14 C of forams 14 C of advected alkenones = -1 permil (infinite 14 C age) Advected alkenone contribution (%) Bermuda Rise Benguela Scotian Margin New England margin Gulf of Mexico Arabian Sea Santa Barbara Basin Indian Ocean NE Pacific Ocean ( (Stn M)) -1 Eglinton et al. unpublished Comparison of alkenone and TOC 14 C ages in surficial (< 3 cm) marine sediments 1 14 C alkenones (permil) Core tops only (-5 cm) C bulk OC (permil) Eglinton et al, unpublished

12 Additional evidence for advective OC supply to the sea floor (i) Increased material fluxes in deep, relative to shallow, sediment traps deployed near continental slopes (Honjo et al., 1982; Biscaye et al., 1988; Thomsen & van Weering, 1998). (ii) High suspended particle concentrations near the seafloor (bottom nepheloid layer; McCave, 1983; Gardner & Sullivan, 1981) or associated with the detachment of intermediate nepheloid layers from the upper slope (INLs; Biscaye et al., 1988; Pickart, 2). (iii) Carbon and oxygen imbalances in the deep ocean (Jahnke et al., 1996). (iv) Old 14 C ages of OC on suspended particles in slope waters (Bauer et al., 21). (v) 14 C age of particles on slope waters intercepted by sediment traps (Anderson et al., 1994; Hwang et al., 24). (vi) The isotopic and molecular composition of deep sea sediments (Freudenthal et al., 21; Benthien & Müller, 2). Advection of POC in the Panama Basin Druffel et al., 1998

13 Lateral transport of alkenones to the Argentine Basin Benthien & Muller, 2 Vertical Transport of Organic Matter to the Sea Floor

14 Lateral Transport of Organic Matter to the Sea Floor 14 C age variability in Bermuda Rise surface (-3 cm) sediment 14 C (permil) G. ruber G. inflata 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 planktonic forams total organic carbon alkenones fatty acids hydrocarbons C21+C23+C25 alkanes C22+C24+C26 alkanes C27 alkane C29+C31 alkanes C28+C3+C32 alkanes UCM C age (yr BP)

15 Calculation of % terrestrial, marine and fossil OC Dual isotopic mass balance approach: 14 C TOC = f marine * marine + f terrestrial * terrestrial + f fossil * fossil δ 13 C TOC = f marine * δ marine + f terrestrial * δ terrestrial + f f ossil * δ fossil f marine + f terrestrial + f fossil = 1 Variable Measurement/assumption: 14 C TOC measure directly (AMS) δ 13 C TOC measure directly (irms) 14 C marine measure phytoplankton sterol (PCGC/AMS) 14 C terrestrial measure lignin phenol/plant wax (PCGC/AMS) 14 C fossil stipulate as 1 δ 13 C marine measure phytoplankton sterol (irm-gc-ms) - assume offset between biomarker and bulk OC δ 13 C terrestrial measure lignin phenol/plant wax (irm-gc-ms) - assume offset between biomarker and bulk OC δ 13 C fossil assume value based on regional stratigraphy - (or measure biomarker selected based on 14 C) Dual Isotope Mass Balance % Arabian Sea Benguela Upwellin Santa Monica Basin Black Sea Unit I Black Sea Unit II marine vascular plant relict Bermuda Rise Washington Margin St Washington Margin St Gulf Of Mexico Beaufort Sea Ross Sea (Chinstra Ross Sea (Gentoo) Ross Sea (Emperor) Ross Sea (Fairy) 14 C TOC δ 13 C TOC Ross Sea (Fairy) Ross Sea (Emperor) Ross Sea (Gentoo) Ross Sea (Chinstrap) Beaufort Sea Gulf Of Mexico Washington Margin St1 Washington Margin St2 Bermuda Rise Black Sea Unit II Black Sea Unit I Santa Monica Basin Benguela Upwelling Arabian Sea

16 Black Carbon (BC) Suggested Reading: Gustafsson O. and Gschwend P.M. (1998) The flux of black carbon to surface sediments on the New England continental shelf. Geochim. Cosmochim. Acta 18, Masiello C.A. and Druffel E.R.M. (1998) Black Carbon in Deep-Sea Sediments. Science 28, Schmidt M.W.I. and Noack a.g. (2) Black carbon in soils and sediments: Analysis, distribution, implications and current challenges. GBC 14, Masiello C.A. (24) New directions in black carbon organic geochemistry. Mar. Chem. 92,

17 Org. Matter + O 2 CO 2 + H 2 O (NB. For PAH, also read BC!)

18 Black Carbon (BC) Some Notes: Estimates of modern BC production Biomass burning: 5-26 Tg C/year Fossil fuel combustion: Tg C/year Atmospheric lifetime of BC aerosols: 4 hours to 1 month Mass of organic carbon stored globally in ocean sediments: 16 Tg/year BC estimated to make up ca. 6% of sedimentary OC globally. Locally (on margins) BC may comprise up to 5% of TOC. Other particulate aerosols Scatter BC Absorb Contributions of Black Carbon to Greenhouse Warming Kirkevag et al. (1999) Tons emitted Tons emitted Fossil Fuel Combustion Biomass Burning Cooke & Wilson (1996)

19 Public Health Increased respiratory problems associated with elevated particulate matter concentrations Black Carbon A moving Target! (The Combustion Continuum) Schmidt et al. (1999)

20 What is Black Carbon? How can we analyze BC?

21 BC isolation/measurement methods 3 main types of method: optical chemical oxidation thermal oxidation NB: In almost all cases, BC is operationally defined. Leads to very different estimates of quantity and flux of BC. Carbon isotopic characterization of BC based on thermal oxidation ( Gustafsson ) method Modified by Reddy

22 Supply of BC to marine sediments Middelburg et al. (1999) Charcoal (%) Age (ka) Interglacial Glacial 2 Verardo & Ruddiman (1996) Proportions of BC in marine sediments

23 14 C age of Black Carbon in marine sediments NB. BC isolated by chemical wet oxidation method Non-BC BC Masiello and Druffel 1998, Science BC in Santa Clara River suspended sediments Masiello and Druffel, 21, GBC

24 BC in Santa Monica Basin sediments Masiello and Druffel 23 GRL Proportions of BC in marine sediments Middleburg et al 1999

25 Graphitic Black Carbon (GBC) in (pre-anthropogenic) Washington Margin sediments Dickens et al. 24, Nature Guo et al. 24, GBC

26 Carbon isotopic composition of dustfall sample off NW Africa Fractions Concn. (gdw basis) δ 13 C ( ) 14 C ( ) 14 C age (yr BP) Total Organic Carbon 1.2 % ± 4 Black Carbon.24 % ± 35 Plant wax alcohols 12 µg ± 143 Eglinton et al., G 3, 22 Molecular Proxies for BC

27 Historical records of combustion inputs to the environment Soot Carbon (g SC / g sed) PAH concentration (ug/g) Year of Deposition Organic Carbon (g OC / g sed) Gustafsson et al. (1997) 188 Pre-188 s: Wood Combustion : Heavy industrialization Utilization of Coal : Change from coal to oil Peak of Pb gasoline use 197-2: Catalytic converters Phase-out of Pb gasoline

28 Pettaquamscutt River Basin 137 Cs (dpm.g -1 ) Year of Deposition ± Depth (cm) ± ± Pb Model 4 Down-core variations in PAH fluxes 2 Flux (ng cm -2 yr -1 ) Year of Deposition Sum of 15 parent PAH (excluding perylene)

29 Assessment of Pyrogenic vs Petrogenic PAH inputs based on molecular parameters 2 mz 192 / phenanthrene mz 216 / pyrene Petrogenic source ratio Petrogenic source ratio 198 Year of Deposition Pyrogenic source ratio Pyrogenic source ratio Ratios from Gustafsson & Gschwend (1997) Flux (ng cm -2 yr -1 ) Retene Year of Deposition Phenanthrene 18

30 Historical variations in PAH 14 C Retene 14 C contents of individual PAH in environmental samples Lima et al in prep.