Outline : Carbon cycling and organic matter biogeochemistry

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Outline : Carbon cycling and organic matter biogeochemistry. Global carbon cycle - pools, sources, sinks and fluxes pools of organic carbon - POC, DOC - vertical & horizontal segregation, vertical fluxes Ocean productivity Biological carbon pump Preservation of organic carbon - PowerPoint PPT Presentation

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  • Outline : Carbon cycling and organic matter biogeochemistry Global carbon cycle - pools, sources, sinks and fluxes pools of organic carbon - POC, DOC - vertical & horizontal segregation, vertical fluxes Ocean productivity Biological carbon pump Preservation of organic carbon Vertical flux of POM sediment traps

    Dissolved organic carbon (DOC) Concentrations & distribution Characterization of DOC pool - molecular size and reactivity Sources and fates of POM & DOM Age and long-term sinks for DOM

  • Operational pools of carbon in seawaterPOM - particulate organic matter (includes not only carbon but also H, O, N, P, S etc)DOM - dissolved organic matter (about 50% C by weight)POC - particulate organic carbon (refers only to the carbon)DOC - dissolved organic carbonPIC Particulate inorganic carbon (CaCO3)DIC - dissolved inorganic carbon (all forms)Organic nutrient poolsPON & POP (the pools of N & P that are bound in organic particles larger than the operational cut-off)DON & DOP - (the pools of N & P that are bound in organic matter that passes through the operational cut-off filter)All pools are operational! (depend on selected criteria for filtration)

  • Organic particle size continuum0.4-0.2 m filtration cut-off

  • Organic carbon = Reduced carbon

    Includes all carbon other than CO2, HCO3-, H2CO3, CO, CO32-, and carbonate minerals

    Includes hydrocarbons CH4, CH3-CH3 etc & black carbon.

    Nearly all reduced carbon is biogenic. However, some chemical/geochemical alteration of OM takes place, petroleum and natural gas formation being notable examples. Because organic matter is mainly biogenic it typically contains not only reduced carbon but also some H, O, N, P and S etc.

  • Atmospheric CO2 784Global Carbon reservoirs and exchanges (Figure based on Libes; data from Table 11.1 in Emerson & Hedges) pools in 1015 gC (boxes) fluxes in 1015 gC y-1 (arrows)Marine biota 1-2Ocean DIC 38,000Detrital POC 30DOC 7000.2Organic sediments10,000,000Fossil fuels 3577Limestone & dolomite50,000,000Terrestrial biota 600Soil & detritus 1500River DIC 0.5Sedimentary reservoirs are huge!Exchange90Net export from surface 8-15

  • Most organic carbon in the sea is dissolved or colloidal.Biomass pools are very smallDissolved and Colloidal materials are operationally Dissolved Operationally-dissolved

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    100000000000000000

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    Relative partitioning of organic carbon in the ocean

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    Dissolved100000000000000000

    Colloidal100000000000000000

    Detritus (POM)30000000000000000

    Phytoplankton3000000000000000

    Zooplankton100000000000000

    Bacteria1000000000000000

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    Relative partitioning of organic carbon in the ocean

  • Sources of organic matter to the open oceansPrimary production Phytoplankton84.4 Macrophytes 6.2

    Rivers 3.65Groundwater0.3Atmospheric input5.45 % of totalRivers are a small source of organic matter to open ocean!Based on Table 9.1 in Millero, 2006

  • Oligotrophic< 0.1 11.0Mesotrophic0.1 -1.0 27.4Eutrophic> 1.0 9.1Macrophytes - 1.0Total ocean production = 48.522.756.518.72.1% of Ocean NPPTotal terrestrial production = 56.4Total global production = 104.9Ocean Net Primary Production in different trophic regimes(
  • Behrenfeld et al 2006. Nature 444:Global primary productivity pattern as deduced from satellite imageryOceanic/oligotrophic areas dominated by picoplankton < 2 mUpwelling, coastal & temperate areas have larger phytoplankton (> 2 m) as major primary producersConsiderations: Depth distribution i.e. euphotic depth Seasonal variations, esp. in polar regions Interannual variations

  • Behrenfeld et al 2006. Nature 444:Temporal changes in global average Chlorophyll anomaly and Net Primary Productivity (NPP) anomaly.1997-98 was a strong El Nino year which reduced NPP. Rapid recovery ensued, with slow decline thereafter.

  • CO2 (g) CO2 (aq) + H2O H2CO3 H+ + HCO3- H+ + CO32-AirSeaPycnoclinePOMCaCO3Some DOMNon-carbonate sedimentCarbon burial & preservation as POM and CaCO3CCDDeep SeaEuphotic zoneDIC & alkalinityrespirationCO2CaCO3 dissolutionThe Biological Carbon PumpExporting carbon below the pycnocline Ridge crestAlkalinityUpwelling of high DIC, high pCO2 waterNo preservation of CaCO3 below CCDspreadingcarbonatesCaCO3-rich sediment above CCDPhotosynthesiscalcificationsinkingPOM

  • Falkowski et al., 1998. Science 298:Export Productionper year

  • Flux of organic matter decreases exponentially with depth :

    POMflux(z) = POMflux (100)(z/100)-0.858

    Where POMflux(100) is the downward flux at the base of the euphotic zone (100 m), and POMflux(z) is the flux of organic carbon at depth (z) measured with sediment traps. At 5000 meters, the flux is only 3.5% of that at the base of the euphotic zone! Vertical flux of POM is via dead phytoplankton, fecal pellets, molt shells, fragments, mucous feeding nets etc. Data for the figure of Bishop et al came from Martin et al. 1987Very little organic matter (POM) reaches the deep ocean and what does reach the bottom is lower quality

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    POM flux as % of flux at 100 m

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    POM flux vs depth based on equation of Bishop (1989)

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    POM flux as % of flux at 100 m

    Depth (m)

    POM flux vs depth based on equation of Bishop (1989)

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  • Hansell et al., 2010Modeled DOC downward fluxDOC/POC downward flux ratioDOC export from surface ocean represents 8-18% of the total organic carbon export.

  • Sediment traps - particle interceptorsBase of euphotic zone 100-200 m500 m1000 m3000 mCapture flux decreases exponentially with depthParticle flux

  • 1-1.5 metersMany different designs of sediment traps have been usedTime series traps - rotating cylinders within trap collect for certain period of timeLarge surface area trap for oceanic sampling

  • Diagram of an automated time-series sediment trap used in the Arabian Sea. A baffle at top keeps out large objects that would clog the funnel. The circular tray holds collection vials. On a preprogrammed schedule (every 5 days to 1 month), the instrument seals one vial and rotates the next one into place. Scientists retrieve the samples up to a year later to analyze the collected sediment. (courtesy Oceanus magazine, WHOI) http://www.whoi.edu/instruments/gallery.do?mainid=19737&iid=10286

  • What results do you expect for POM captured in a sediment trap array deployed over a full oceanic depth profile? Quantity of POM? Quality of POM - C:N, specific biomolecules?, 14C-content?

  • Three sediment trap designs. The original funnel design (moored trap) uses a large collection area to sample marine particulates that fall to great depths.Surface waters produce enough sediment so that traps there dont require funnels. Neutrally buoyant, drifting sediment traps catch falling material instead of letting it sweep past in the current. Drawings are not to scale.Source: http://www.whoi.edu/instruments/gallery.do?mainid=19735&iid=10286

  • Joaquim Goes and his team deploy simple sediment traps in the Southern Ocean

  • WHOI scientists Ken Buesseler and Jim Valdes with one of the neutrally buoyant sediment traps they helped design. The central cylinder controls buoyancy and houses a satellite transmitter. The other tubes collect sediment as the trap drifts in currents at a predetermined depth, then snap shut before the trap returns to the surface. (Tom Kleindinst, WHOI)http://www.whoi.edu/instruments/gallery.do?mainid=19750&iid=10286

  • Much of the present global carbon burial (preservation) is in marine environments Little organic carbon preservation in terrestrial soils except for high latitude peats. Terrestrial burial of OM has been more significant in the geological past (i.e. Carboniferous coal deposits)Significance of Organic Carbon Burial

    Burial and preservation of biogenic (reduced) carbon in sedimentary reservoirs removes atmospheric CO2 and allows excess O2 to remain in the atmosphere.

    Burial of organic matter removes some nutrient elements and trace elements.

    Carbon burial leads to petroleum, organic rich shales, & natural gas

  • >5000 m depth>2-5000 m depth>2000 m depth incl. Black Seay = 0.028 x1.25The greater the overall sedimentation rate of particles, the greater the fraction of surface primary production delivered to sedimentsSee Fig. 11.5 in Pilson for actual data graph

  • Libes, Chapter 25Burial will be a small fraction of the carbon delivered to the sediments. Most will be respired to CO2 and diffuse back to water column.

  • Reasons for high carbon burial on the continental margins:

    high productivity - > high POM flux to benthos high particle flux leading to faster burial rate - OM preservation tied directly to mineral surface area (see Keil et al. 94) shallow depth - less organic matter degradation on descent remineralization slower under anoxia - still a debatable issue.

  • Dissolved organic carbon - the largest pool of organic matter in seawaterMeasured by converting DOC into CO2 via: Wet-chemical oxidation High temperature catalytic combustion UV-oxidation Sealed tube combustionDOC concentrations are 70-100 M in surface waters of the open ocean, and 35-50 M at depth. Coastal waters can have much higher DOC

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    Vertical profile of DOC concentrations in the ocean

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  • Surface ocean (30 m) DOC concentrations Dots are measured values, background color field is modeledHansell et al., 2010

  • Deep ocean (3000 m) DOC concentrations decrease along ocean conveyor (meridional overturning circulation)Dots are measured values, background color field is modeledHansell et al., 2010The semi-labile fraction of DOC degrades during the long transit from North Atlantic to the Pacific. What is left (~34 M) is ultra-refractory since it survived the ~1000 y trip through the deep ocean. This DOC is present as background DOC in surface waters and has an average age of ~6000 years.

  • Ultra-refractory DOC; = >6000 y

    Refractory DOC; = ~1000 years

    Semi labile DOC; larger pool (25-30 M) in sfc; = weeks to monthsLabile DOC; Small pool; = hours to daysOpen ocean surface DOC concentration is about 70 M. It is about 44 M in the deep Sargasso and about 34 M in the deep Pacific. 010203040506070After Benner, 2002

  • The average 14C age of deep DOC is 6000 years|!

  • DOC is generally conservative with salinity in estuariesFreshwater end-memberSeawater end-member ~80-100 MImplies terrestrial DOC delivery to ocean but most is lost on shelf (see next slide)In fact, some modification of riverine DOC takes place in estuaries, but conservative pattern still observed

  • DOC concentration decreases away from shore

  • Constituents of DOMHigh molecular weight >5000 Da (includes colloids) proteins polysaccharides (mucus, structural polymers) nucleic acids some humic substancesMedium Molecular weight 500-5000 Da humic substances (refractory) oligopeptides, oligonucleotides lipids pigmentsLow molecular weight < 500 Da monomers (sugars, amino acids, fatty acids) osmolytes (DMSP, betaines, polyols) toxins, pheromones and other specialty chemicalsSee Chapter 22 in Libes for structures of organic compounds

  • Shift

  • Examples of some polysaccharides that might be part of a semi-labile, high molecular weight pool of DOM. Chitin is an amino sugar, i.e. it contains NPectin contains O-methoxy groups

  • Depolymerization - Polymer hydrolysis

    Conversion of high molecular weight DOM or POM into low molecular weight DOM

    Carried out primarily by bacteria but really a consortium of microbes.

    Proteins -> free amino acids & peptides by proteases Polysaccharides to monosaccharides by glucosidases, chitinases, cellulases Peptides to amino acids by peptidases RNA or DNA to nucleotides by nucleases

  • Origin of labile DOM in seawater

    Exudates - Amino acids, sugars, some high molecular weight labile polysaccharides - rapidly consumed Death or lysis of cells - rapid uptake by bacteria Sloppy feeding - leaking of phytoplankton cell contents Digestion - Digestor theory. Jumars, Penry et al. Zooplankton maximize their organic matter assimilation by maximizing throughput not by being highly efficient. This results in considerable release of DOC from fecal pellets and zooplankton.

  • Marine Snow. Agglomerated organic matter - amorphous aggregates Enriched with bacteria and protozoans possible low oxygen conditions elevated nutrients Still understudied.

    Some species of phytoplankton release mucilage i.e. Phaeocycstis sp.

    TEP - Transparent ExoPolymer. Is a form of marine snow

    Marine Snow or aggregates caused by surface phenomenon. Enrichment of OM at surfaces of bubbles, waves convergence zones. You can make snow in the lab by rotating filtered water samples in bottle. Snow, and DOC make, sea foam.

  • Phaeocystis globosa colony cells embedded in mucous form spherical colonySea foam generated from Phaeocystis bloom in Dutch Wadden Sea...

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