University:
Widener University
Course:
CHEM-255 | Organic Chemistry I
Academic year:

2023
Views:

172

Pages:

34
Author:

vladinomcue

Biogeochemical cycling of dissolved organic C and nutrients The profile of [DOC] With depth in the ocean 1. Measured by HTCO or wet chemical oxidation 2. Surface values are 60-80µM C deep sea values are 40 µM C 3. Deep sea values are nearly constant (implies some tight feedback/control) 4. Global inventory is 680 GT C. Most Resides in the deep ocean! Why 40 µM C? What processes set the global inventory of marine organic carbon? Solar Variability Cosmic Rays Geomagnetic Field Intensity ∆ 14C Cycle 14CO 14C 2 Production Distribution among C reservoirs Atm Surf Surf Bio/Soils CaCO3 Seds Deep Deep Figure removed due to copyrite restrictions. Source Unknown. Pioneered by Pete Williams At SIO. Contamination is a big problem!!! Does UV get it all ? Pre AMS 1g C (1m3) Now about 1mg C (1L) Radiocarbon in DOC and DIC CO2->DIC->POC->DOC DOC DIC DOC is depleted (older) than DIC at all depths There is a source of new DOC in the surface ocean The ∆∆14C between DIC and DOC is not the same at all depths (greater at the Surface) Radiocarbon in the Atlantic and Pacific Oceans DIC 14C has the same Value in the Atl and Pac ∆∆14C of DIC and DOC is about the same in the deep Atl and Pac oceans Deep ocean values are equal to a RC age of Several 1000’s years Either there is a source of “old” DOC, or DOC lasts for several ocean mixing cycles Why is DOC old in surface water? Why is DOC old in surface water? Old DOC ∆14C = DOC(deep) Why is DOC old in surface water? New DOC ∆14C=DIC Why is DOC old in surface water? Atlantic surface water = -120 ‰ 14C obs = -127 ‰ Old DOC ∆14C = DOC(deep) 14C New DOC ∆14C=DIC calc Pacific surface water 14C = -147 ‰ 14C obs = -148 ‰ calc What flux of carbon is needed to maintain the marine DOC reservoir? Global inventory/residence time = annual flux 680 GT C/ 5000-6000 yr = 0.11-0.14 GT C/yr !!! How does this compare with other C fluxes? What is the source of Marine DOC ? Stable C isotopes Marine C -21‰ Terrestrial C C3 plants -27‰ C4 plants -15‰ Hard problems in oceanography- what is DOC and why is it so old?? DOC = humic substances Sampling DOC is hard to do… DOC= 1mg/L C Salt = 35g/L Separation based on size Cross Flow Filtration High Pressure 1 nm pore @ 1 kD Selects for HMW fraction about 30-35% TOC Low Pressure Membrane effects what Is collected Some salts collected too! 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter C/N = 15+3 13C Nuclear Magnetic Resonance Spectrum of high molecular weight dissolved organic matter OCO (12%) COOH CONH (10%) HCOH (55%) CHx (10%) 1HNMR of high molecular weight DOC HCOH CH3CO- CHx OCO aromatic HMWDOC, what could it be? From our knowledge of cell biochemicals… Proteins C/N = 4, CHx(O):CON = 3:1 Carbohydrates C only ? OCO:HCOH 1:5 Lipids C only CHxCOOH CHxCOH ……..looks to be mostly (50-70%) carbohydrate ! 280 µM C 80-100 µM C Relative abundance of major biochemcials in HMWDOC HMWDOC in freshwater and marine environments Polysaccharide Analysis 2 3 1 O O 2 3 0 4 2 Fructose, Glucose 3 Sucrose O H+ 56 7 4 Minutes 8 hydrolysis Relative % Relative abundance of sugars in HMWDOC HMWDOC monosaccharides in rivers,lakes, and seawater Image removed due to copyright restrictions. Locations of sampling: Eel River Lake Superior Nobska Pond Delaware River Mississippi River BUT…..yields of sugars are only 5-15% HMWDOC 1HNMR of high molecular weight DOC HCOH CH3CO-? CHx OCO aromatic 15N-NMR of HMWDOC. Is HMWDON from protiens or from amino sugars? Amide (RCON) (90-100%) amino sugars O CH3CONH Free amine (R-NH2) (0-10%) RC(O)NC(R)C(O) Is a large fraction of HMWDOC and HMWDON from amino sugars or proteins? amino sugars proteins O RC(O)NC(R)C(O) RC(NH2)COOH (amino acids) X CH3CONH O CH3CONH Is a large fraction of HMWDOC and HMWDON from amino sugars? O CH3CONH H+ O X HNH CH3COOH X What is the ‘lipid” in HMWDOC? Lipid HCOH CH3CON CHx CH3(CH2)nCOH CH3(CH2)nCOOH Deoxy sugars OCO H2COH O CH3 O There are really “two” types of lipid in HMWDOC CH3COOH CHx The effect of periodate on HMWDOC Is the lipid really lipid? Lipid HCOH CH3CON RCOH No Reaction CHx OCO Deoxy sugars CH3 O CH3COOH Periodate oxidation of HMWDOC NaIO4 ∆ 80oC HMWDOC composition summary Direct chemical analyses show that HMWDOC is 50-70% carbohydrate, 5-6% acetamide, and 5-6%”lipid” Chemical hydrolyses techniques show HMWDOC to be 15% carbohydrate, 3-5% protein, and <1% lipid Indirect chemical analyses show that an additional 25% Is amino sugars, and 25% is deoxysugars. However, There is no direct confirmation of this. A good portion of >25% remains uncharcterized. Much more at the molecular level.

DOC, DON, DOP Cycling and Composition (cont.)

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