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Published byMateusz Stefański Modified over 6 years ago
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Dissolved Organic Matter- what is inside the black box?
What is the relationship between organic matter composition, microbial diversity & production? How is microbial metabolism coupled to organic matter structure? How does DOM affect microbial adaptation & evolution? What sets the ocean inventory of organic carbon, and why is so much organic carbon preserved in seawater? Why do organic nitrogen and phosphorus accumulate in nutrient limited regions of the surface ocean where they are most needed, but disappear in the mesopelagic ocean where they are not needed?
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DOC sampling is hard to do… Isolation of DOM by ultrafiltration
Separation based on size 1 nm 1 kD Selects for HMW fraction about 30-35% TOC Membrane effects what Is collected Some salts collected too!
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DOC sampling filter (1 nm) sample concentrate (> 1000 MW) pump
filtrate (< 1000 MW)
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Ultrafiltration high molecular weight DOM (HMWDOM)
membrane filter >1000 D DOM fraction 30-35% DOC < 1000 D DOM fraction 65-70% DOC
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Final product 30-35% of total DOC
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DOM analysis by Nuclear Magnetic Resonance spectroscopy
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13C Nuclear Magnetic Resonance Spectrum
of high molecular weight dissolved organic matter (HMWDOM) Frequency Abundance
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13C Nuclear Magnetic Resonance Spectrum
of high molecular weight dissolved organic matter (HMWDOM) Frequency Different types of carbon resonate at different frequencies Area is proportional to the amount of carbon Abundance ppm
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1H, 31P, 15N - NMR spectra of HMWDOM
Clark et al L&O 2001
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from the Atlantic and Pacific
13CNMR spectra of HMWDOM from the Atlantic and Pacific Sargasso Sea NPSG 3 m 3 m
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13CNMR of marine phytoplankton*
Fragilariopsis cylindrus Phaeocystis antarctica *Adina Paytan, 2005
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13CNMR of plankton tows Hedges et al GCA 2001
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13CNMR of HMWDOM in different
aquatic environments North Pacific Ocean Great Salt Lake Leenher et al., (2004) Biogeochem. 69, A significant fraction of HMWDOM is the same in all aquatic environments HMWDOM has a different composition than marine than marine phytoplankton Suggests selective preservation of a component of POM Most of the C is carbohydrate (APS) large global inventory Andrews Creek, RMNP McKnight et al. (1997) Biogeochem. 62,
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HMWDOM in the deep sea Sargasso Sea NPSG 3 m 3 m 2500 m 1800 m
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13C Nuclear Magnetic Resonance Spectrum
of high molecular weight dissolved organic matter
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13C Nuclear Magnetic Resonance Spectrum
of high molecular weight dissolved organic matter COOH CONH (10%)
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13C Nuclear Magnetic Resonance Spectrum
of high molecular weight dissolved organic matter OCO (12%) COOH CONH (10%)
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13C Nuclear Magnetic Resonance Spectrum
of high molecular weight dissolved organic matter OCO (12%) HCOH (55%) COOH CONH (10%)
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C/N = 15 +/- 3 13C Nuclear Magnetic Resonance Spectrum
of high molecular weight dissolved organic matter OCO (12%) HCOH (55%) C/N = 15 +/- 3 COOH CONH (10%) CHx (10%)
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C/N = 15 +/-3 13C Nuclear Magnetic Resonance Spectrum
of high molecular weight dissolved organic matter OCO (12%) HCOH (55%) C/N = 15 +/-3 HCOH OCO = 4-5 COOH CONH (10%) CHx (10%)
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HMWDOC, what could it be? From our knowledge of cell biochemicals…
Proteins C/N = 4, CHx(O):CON = 3 Carbohydrates C maybe N HCOH:OCO = 5 Lipids C only CHx:COOH = 18 CHx:COH = 30
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HMWDOC, what could it be? From our knowledge of cell biochemicals…
Proteins C/N = 4, CHx(O):CON = 3 Carbohydrates C maybe N HCOH:OCO = 5 Lipids C only CHx:COOH = 18 CHx:COH = 30 ……..looks to be mostly (50-70%) carbohydrate !
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Spectral and chemical analyses of HMWDOC
Carbohydrate 50-70% of HMWDOC 200 150 100 50 -O- -O- 13CNMR Acid hydrolysis
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Spectral and chemical analyses of HMWDOC
Acid hydrolysis followed by Monosaccharide analyses yields 7 major neutral sugars that represent 10-20% of HMWDOC in surface water Carbohydrate 50-70% of HMWDOC 200 150 100 50 13CNMR R F A X Gl M Ga Acid hydrolysis
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NMR and carbohydrate analyses of deep sea HMWDOC
monosaccharide distribution surface relative % deep relative %
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Can we use the 14C of pure sugars to determine
If they are part of the reactive or nonreactive fraction of DOC? reactive DOC 14C=DIC “nonreactive” DOC 14C = DOC(deep)
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Radiocarbon analyses of HMWDOC carbohydrates
Sample Hawaii NPSG DIC ‰ (n=4) 89+7‰* Glucose 47, Galactose Mannose Xylose 52, Arabinose ND Fucose 49, Rhamnose 40, Average 56+6‰ ‰ *data from Ellen Druffel
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Can 14C in sugars constrain the turnover time of
The “semi-reactive” fraction of DOC? Assume the concentration of reactive DOC is at steady state,and that it produced each year with a 14C value equal to DIC. Each year a fraction of the sugars are non-selectively removed and the 14C value for the remainder is calculated.
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O = -C-N -C-NH2 What else is in HMWDOC ? 15N NMR (90-98%) Amide-N
Amino-N (2-10%)
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-C-N- O What else is in HMWDOC ? 15N NMR proteins Amide-N Amino-N
amino sugars CH3CONH
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Is a large fraction of HMWDOC and HMWDON
from amino sugars? 15N NMR 1HNMR Amide-N Acetate
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Is a large fraction of HMWDOC and HMWDON
from amino sugars? 15N NMR 1HNMR Amide-N Acetate HNOCCH3 HNOCCH3
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Is a large fraction of HMWDOC and HMWDON
from amino sugars? HNOCCH3 Amide-N Amide-N Amino-N HNH HNH
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Is a large fraction of HMWDOC and HMWDON
from amino sugars? 15N 1H CH3CONH acid HNH HNH + CH3COOH
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Composition and cycling of HMWDOM
Most of the carbon (75%) is carbohydrate Half the N is from aminosugars, about 10% is from proteins The sugar/aminosugar fraction is the “semi-labile: DOC that accumulates in surface water this may fuel about 50% of microbial production in surface waters. Why does it accumulate? Surface HMWDOM
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What is the composition of Non-reactive DOC in the deep ocean
(1800 m Pacific)
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Non-reactive DOM Semi-reactive DOM Very reactive DOM O -C-N- CH3 O HO
Mostly polysaccharides Biopolymers… 80-90% of cell C-N-P Don’t really Know Humic substances? Free amino acids Simple sugars Urea…etc. 10-20% of cell C-N-P
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Non-reactive DOM Semi-reactive DOM Very reactive DOM Humic substances
Proteins Polysaccharides Biopolymers… 80-90% of cell C-N-P Free amino acids Simple sugars Urea…etc. 10-20% of cell C-N-P Concentration = 40 µM 25-40 µM 100 nm-1µM (?) Inventory = 650 GT C 30-50 GT C GT C 14C= -400 to -600‰ 14C= ‰ (?) 14C= ‰ Annual flux = 0.1 GTC Moderate to large ? Large
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