Outline : Carbon cycling and organic matter biogeochemistry  Global carbon cycle - pools, sources, sinks and fluxes pools of organic carbon - POC, DOC.

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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
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  • Operational pools of carbon in seawater POM - 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 carbon PIC Particulate inorganic carbon (CaCO 3 ) DIC - dissolved inorganic carbon (all forms) Organic nutrient pools PON & 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)
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  • Organic particle size continuum 0.4-0.2 m filtration cut-off
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  • Organic carbon = Reduced carbon Includes all carbon other than CO 2, HCO 3 -, H 2 CO 3, CO, CO 3 2-, and carbonate minerals Includes hydrocarbons CH 4, CH 3 -CH 3 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.
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  • Atmospheric CO 2 784 Global Carbon reservoirs and exchanges (Figure based on Libes; data from Table 11.1 in Emerson & Hedges) pools in 10 15 gC (boxes) fluxes in 10 15 gC y -1 (arrows) Marine biota 1-2 Ocean DIC 38,000 Detrital POC 30 DOC 700 0.2 Organic sediments 10,000,000 Fossil fuels 3577 Limestone & dolomite 50,000,000 Terrestrial biota 600 Soil & detritus 1500 River DIC 0.5 Sedimentary reservoirs are huge! Exchange 90 Net export from surface 8-15
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  • Most organic carbon in the sea is dissolved or colloidal. Biomass pools are very small Dissolved and Colloidal materials are operationally Dissolved Operationally-dissolved
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  • Sources of organic matter to the open oceans Primary production Phytoplankton84.4 Macrophytes 6.2 Rivers 3.65 Groundwater0.3 Atmospheric input5.45 % of total Rivers are a small source of organic matter to open ocean! Based on Table 9.1 in Millero, 2006
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  • Trophic zone Mixed layer Chl a (g L -1 ) Net Primary Production (10 15 gC y -1 ) Oligotrophic< 0.1 11.0 Mesotrophic0.1 -1.0 27.4 Eutrophic> 1.0 9.1 Macrophytes - 1.0 Total ocean production = 48.5 22.7 56.5 18.7 2.1 % of Ocean NPP Total terrestrial production = 56.4 Total global production = 104.9 Ocean Net Primary Production in different trophic regimes (
  • Behrenfeld et al 2006. Nature 444: Global primary productivity pattern as deduced from satellite imagery Oceanic/oligotrophic areas dominated by picoplankton < 2 m Upwelling, coastal & temperate areas have larger phytoplankton (> 2 m) as major primary producers Considerations: Depth distribution i.e. euphotic depth Seasonal variations, esp. in polar regions Interannual variations
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  • 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.
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  • CO 2 (g) CO 2 (aq) + H 2 O H 2 CO 3 H + + HCO 3 - H + + CO 3 2- Air Sea Pycnocline POMCaCO 3 Some DOM Non-carbonate sediment Carbon burial & preservation as POM and CaCO 3 CCD Deep Sea Euphotic zone DIC & alkalinity respiration CO 2 CaCO 3 dissolution The Biological Carbon Pump Exporting carbon below the pycnocline Ridge crest Alkalinity Upwelling of high DIC, high pCO 2 water No preservation of CaCO 3 below CCD spreading carbonates CaCO 3 -rich sediment above CCD Photosynthesis calcification sinking POM
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  • Falkowski et al., 1998. Science 298: Export Production per year
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  • Flux of organic matter decreases exponentially with depth : POM flux(z) = POM flux (100) (z/100) -0.858 Where POM flux(100) is the downward flux at the base of the euphotic zone (100 m), and POM flux(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. 1987 Very little organic matter (POM) reaches the deep ocean and what does reach the bottom is lower quality
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  • Hansell et al., 2010 Modeled DOC downward flux DOC/POC downward flux ratio DOC export from surface ocean represents 8-18% of the total organic carbon export.
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  • Sediment traps - particle interceptors Base of euphotic zone 100-200 m 500 m 1000 m 3000 m Capture flux decreases exponentially with depth Particle flux Poison or preservative Baffle to reduce hydrodynamic effects
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  • 1-1.5 meters Many different designs of sediment traps have been used Time series traps - rotating cylinders within trap collect for certain period of time Large surface area trap for oceanic sampling
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  • 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
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  • 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?, 14 C- content?
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  • 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/instru ments/gallery.do?mainid=1 9735&iid=10286
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  • Joaquim Goes and his team deploy simple sediment traps in the Southern Ocean
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  • 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/instrume nts/gallery.do?mainid=19750 &iid=10286
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  • 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 CO 2 and allows excess O 2 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
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  • Sediment accretion rate (cm per 1000 y) 0.11101001000 0.001 0.01 0.1 1 10 100 Percent of primary production accumulated in the sediments >5000 m depth >2-5000 m depth >2000 m depth incl. Black Sea y = 0.028 x 1.25 The greater the overall sedimentation rate of particles, the greater the fraction of surface primary production delivered to sediments See Fig. 11.5 in Pilson for actual data graph Coastal areas maximum of ~10%
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  • Most burial nearshore on continental margins Libes, Chapter 25 Burial will be a small fraction of the carbon delivered to the sediments. Most will be respired to CO 2 and diffuse back to water column.
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  • 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.
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  • Dissolved organic carbon - the largest pool of organic matter in seawater Measured by converting DOC into CO 2 via: Wet-chemical oxidation High temperature catalytic combustion UV-oxidation Sealed tube combustion DOC 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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  • Surface ocean (30 m) DOC concentrations Dots are measured values, background color field is modeled Hansell et al., 2010
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  • Deep ocean (3000 m) DOC concentrations decrease along ocean conveyor (meridional overturning circulation) Dots are measured values, background color field is modeled Hansell et al., 2010 The 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. NADW starts with about 46 M DOC
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  • AB C D DOC Concentration (M) 1000 2000 3000 4000 0 Depth (m) Ultra- refractory DOC; = >6000 y Refractory DOC; = ~1000 years Semi labile DOC; larger pool (25-30 M) in sfc; = weeks to months Labile DOC; Small pool; = hours to days Open 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. 0 10 20 30 40 50 60 70 After Benner, 2002
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  • The average 14 C age of deep DOC is 6000 years|!
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  • DOC (M) Salinity 36 0 0 400 75 DOC is generally conservative with salinity in estuaries Freshwater end-member Seawater end-member ~80-100 M Implies 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
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  • DOC concentration decreases away from shore Much of the DOC delivery to ocean is lost on the shelf, close to shore
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  • Constituents of DOM High molecular weight >5000 Da (includes colloids) proteins polysaccharides (mucus, structural polymers) nucleic acids some humic substances Medium Molecular weight 500-5000 Da humic substances (refractory) oligopeptides, oligonucleotides lipids pigments Low molecular weight < 500 Da monomers (sugars, amino acids, fatty acids) osmolytes (DMSP, betaines, polyols) toxins, pheromones and other specialty chemicals Moderate lability Mixed lability some very refractory High lability See Chapter 22 in Libes for structures of organic compounds
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  • Shift
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  • 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 N Pectin contains O-methoxy groups
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  • 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
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  • 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.
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  • 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 TEP - Transparent ExoPolymer. Is a form of marine snow sea foam 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.
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  • http://www.microscopy-uk.org.uk/mag/artapr01/foam.html http://www.ifremer.fr/delec-en/projets/efflores%20phyto/phaeocystis/phaeocys.htm Phaeocystis globosa colony cells embedded in mucous form spherical colony Sea foam generated from Phaeocystis bloom in Dutch Wadden Sea
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  • Nags Head, N.C. High winds blow sea foam into the air as a person walks across Jeanette's Pier in Nags Head, N.C., Sunday, Oct. 28, 2012 as wind and rain from Hurricane Sandy move into the area. Governors from North Carolina, where steady rains were whipped by gusting winds Saturday night, to Connecticut declared states of emergency. Delaware ordered mandatory evacuations for coastal communities by 8 p.m. Sunday. (AP Photo/Gerry Broome) Blowing sea foam at Nags Head, North Carolina during Hurricane Sandy, October 2012
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  • Biogeochemists rule # 1 What isnt there may be most important! Substances with low concentrations may be especially important in biogeochemical fluxes - their concentrations are low because they are desirable molecules to microbes! This axiom isnt always true, but it often is
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  • Concentrations of most labile, low m...


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