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Chemical Characterization of Dissolved Carbon, Nitrogen, and Phosphorus in the Open Ocean

Chemical Characterization of Dissolved Carbon, Nitrogen, and Phosphorus in the Open Ocean. (What is Dissolved Organic Matter?). Dissolved Organic Matter Composition – The Problem. Salt. DOC. Cross or tangential flow filtration, Ultra- or nanofiltration. Separation based on size

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Chemical Characterization of Dissolved Carbon, Nitrogen, and Phosphorus in the Open Ocean

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  1. Chemical Characterization of Dissolved Carbon, Nitrogen, and Phosphorus in the Open Ocean (What is Dissolved Organic Matter?)

  2. Dissolved Organic Matter Composition – The Problem Salt DOC

  3. Cross or tangential flow filtration, Ultra- or nanofiltration Separation based on size 1 nm pore @ 1 kD Selects for larger size (High Molecular Weight) fraction About 30-35% TOC (now up to 60% using electrically assisted UF) Membrane effects what is collected

  4. DOC sampling via ultrafiltration filter (1 nm) sample concentrate (> 1000 MW) pump filtrate (< 1000 MW)

  5. Ultrafiltration of high molecular weight DOM (HMWDOM) >1000 D DOM fraction < 1000 D DOM fraction

  6. Ultrafiltration yields a largely salt free powder of about 20-30% of the total DOC in seawater. Elemental analysis yields a C/N/P ratio of 15-18/1 and a C/P ratio or 300-1000/1 Not Redfield – much lower in N and P

  7. Nuclear Magnetic Resonance Spectroscopy (NMR) Can be tuned to different Nuclei of interest (C,N,P…). Gives information on functional groups which, combined with a knowledge of biochemicals can be used to deduce composition and origin. Internally quantitative.

  8. 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter (C/N = 15) Frequency Abundance 250 200 150 100 50 0

  9. 13CNMR of plankton tows 13CNMR of HMWDOM Sargasso Sea (surface) Chemical shift (ppm) Hedges et al GCA 2001

  10. 13CNMR spectra of HMWDOM North Pacific Subtropical Gyre Sargasso Sea 3 m 3 m

  11. HMWDOM in the deep sea Sargasso Sea NPSG 3 m 3 m 2500 m 1800 m Slide 5.17

  12. 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter (C/N = 15) HCOH HCNH (55%) OCO (12%) COOH CONH (10%) CHx (10%) Slide 5.11 250 200 150 100 50 0

  13. Spectral modeling of major biochemicals in DOM Peptides Peptides Carbohydrates Carbohydrates CRAM CRAM Surface Water Deep Water

  14. A large fraction of semi-reactive DOM that accumulates in surface seawater is a complex carbohydrate of unknown origin

  15. Isolation of DOM by adsorption onto hydrophobic resins Seawater (filtered; pH = 2) Selective chemical Adsorption 10-20% of DOC Methanol or Ammonium hydroxide wash

  16. DOM analysis by high resolution mass spectrometry Approximately 1000-2000 ions Between 300-1000 MW

  17. DOM analysis by high resolution mass spectrometry

  18. DOM analysis by high resolution mass spectrometry Exact mass 499.1183 C32H18O6

  19. Elemental Analysis of DOM in Weddell Sea Seawater Hertkorn

  20. Unusual molecular masses in DOM Surprisingly, there is a population of very low H/C and O/C organic matter

  21. Is a portion of DOM in the ocean of thermogenic (high temperature) origin? Biomass burning? Fossil fuel combustion Hydrothermal processes? Dittmar & Paeng Nature 2009

  22. Using “designer” solid phase extraction and mass spectrometry to Target organic matter of particular interest 71-76% of DOP removed by MnO2

  23. OH R – O-P=O m/z = 79 OH Phosphate OH R - P=O OH Phosphonate

  24. HO -C-N- O O O O -C-N- CH3 CH2 CH2 -C-N- Composition, reactivity, flux and distribution of DOM Non-reactive DOM Semi-reactive DOM Very reactive DOM Biopolymers (polysaccharides, proteins)* Concentration 0-40 µM Inventory = 10-20 GT C 14C= modern (DIC) Annual flux = 10’s GT C? * = 80% of cell C, N Simple biomolecules (amino acids, sugars)* Concentration 1-2 µM Inventory = 0.1-0.3 GT C 14C= modern (DIC) Annual flux = 10’s GT C? * = 10-20% of cell C, N Aliphatic or “Humic” substances Concentration 40 µM Inventory = 640 GT C 14C= -400 to -600‰ Annual flux = 0.1 GTC

  25. Summary DOM is isolated from seawater using either adsorption onto hydrophophic resin or ultrafiltration (molecular filtration). Adsorptive techniques selects DOM that has a high affinity for the adsorption media, while ultrafiltration relies on the hydrodynamic diameter of the organic matter. Adsorptive techniques select for DOM that is depleted in radiocarbon, while ultrafiltration selects for “HMWDOM” that is enriched in radiocarbon. The old, hydrophobic fraction of DOM is relatively more enriched in aliphatic carbon and highly oxidized, with a high COOH/CHx ratio. Mass spectral analysis suggests a protion of this may be of thermogenic origin. NMR analysis of HMWDOM shows it to have a remarkably uniform distribution of functional groups that is conserved across ocean basins. Carbohydrates are the dominant biochemical class present in HMWDOM. Chemical hydrolysis only recovers 10-20% of carbohydrate as neutral sugars, characterized by seven major neutral sugars (rhamnose, fucose, arabinose, mannose, glucose, xylose, galactose). These data suggest that the HMWDOM is a biopolymer with a specific composition.

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