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ChemicalOceanographyRyan Lecture 9 - April 8, 2004

Dr. David K. RyanDepartment of ChemistryUniversity of Massachusetts Lowell&Intercampus Graduate Schoolof Marine Sciences and Technology

http://faculty.uml.edu/David_Ryan/84.653

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Organic Compounds in the SeaWhere do they come from?What are they? POCWhy are they important? � DetritusWhere do they go? � Fecal Mat.

DOC� Biological molecules (lipids,

proteins, carbohydrates, etc., etc.)� Hydrocarbons� Humic Materials (=other stuff)

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Morel, 1983

What is this stuff?

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520

Libes, 1992

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Humic Materials or Humic SubstancesComplex organic molecules of natural originMuch is known about properties/importanceSome is known about structural componentsLittle is known about exact chemical nature or exact structure – because:� Complexity � Deficiencies in analytical� Heterogeneity techniques� Concentrations � Interfering species

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Libes,1992

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Millero,1996

um)

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Carbon CycleLibes, 1992

Inventories in1015 g C = BMT

Fluxes (arrows)1015 g C/yr

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Cauwet, 1978

Distribution ofOrganic Carbon

(a) Major compartmentsin the global ocean

(b) Major compartmentsfor the planet

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Active Carbon Reservoirs(excluding Ocean DIC)

Soil IC22%

Atm. CO213%

Terr. Plants19%

Ocean DOC12%

Surf. Ocean Seds.

3%

Soil OC32%

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Organic Compounds in the SeaWhere do they come from?What are they?

�Hydrocarbons�Carbohydrates (polysaccharides), sugars�Lipids, fats, waxes, oils, fatty acids�Pigments�Nucleic acids, RNA, DNA�Amino acids, polypeptides, proteins, enzymes�Low molecular weight carboxylic acids�Humic Substances

Bio & Geo

Bio

?

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Organic Carbon Inputs to SW

Allochthonous = formed externally (ex situ)Autochthonous = formed internally (in situ)

Most Marine Humic Material is formed in situthrough a combination of biotic & abioticprocesses

Some Humic Material (i.e., coastal) is introduced from terrestrial sources (formed on land)

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Transformation of DOCBiological molecules are labile = readily broken down or degraded fastBy-products of this breakdown (substances not completely remineralized) can react with other organic compounds in a process called Humification or Early DiagenesisThis results in fairly non-labile HumicMaterialsHumics may degrade slowly or be removed to the sediments (refractory or non-labile)

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Transformation of DOC

These processes occur in water column, in sediments, and in soilsHumification is the first step, fast, aerobicFossilization or carbonification occur more slowly on geologic time scales, anaerobicly, after burial in sedimentsDiagenesis, Catagenesis, Metagenesis

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Humification ofOrganic Matter(possible scheme)

Libes, 1992

Hydrocarbons, Fats, WaxesOils, Sterols, Vitamins, etc.

Biotic

Abiotic

Macromoloecules

aggregationagglomeration

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Humification ofOrganic Matter(another scheme)

Libes, 1992

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Morel & Hering,1993

20Humic Structure Proposed by Schnitzer (Rashid 1985)

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Structure Attributed to Gamble et al. (1985)

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Morel & Hering (1993) Based on Aiken et al. (1985)

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Possible StructuralUnits Set Forth byAverett, Leenheer,McKnight & Thorn(1989) From Morel& Hering, 1993

24Kleinhempel reprinted from Albrecht Thaer Archiv (1970)

25Organic Solute Macromolecule (ORSMAC) Leenheer (1985)

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Davies & Ghabbour, 1999

Carbon atoms-greenOxygen atoms-redNitrogen-blueHydrogen not shown

Molecular model of the lowestenergy conformation ofhumic acid building blocks

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Importance of Humic MaterialsGlobal Carbon ReservoirTake Part in Interfacial PhenomenaUndergo Coagulation and AggregationInvolved in Photochemical ReactionsContain RadicalsKnown Reducing AgentsMethylate MetalsForm Chlorinated Species, THMs DBPsDetoxify MetalsLimit Bioavailability of MetalsAlter SolubilityInfluenceBind Metals & Organic PollutantsTerminal Electron Transport Acceptor for Bacteria

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Fox, 1983

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CDOM = Chomophoric (Colored) Organic Matter

Photochemistry

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Metal Complexation by Humics

Leenheer et al. (1998) Morel (1983)

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References

Cauwet, G. (1978) Oceanologica Acta 1, 99Davies & Ghabbour (1999) Chemistry & Industry 7, 426Fox, L. (1983) Estuarine Coastal Shelf Sci. 16, 431Hedges, J.I. (1992) Global Biogeochemical Cycles: Progress

and Problems, Mar. Chem. 39, 67Leenheer, J.A. (1985) in Humic Substances in Soil Sediment

and Water: Geochemistry, Isolation and Characterization, Wiley, NY, pp. 409-429

Lenheer, J.A. et al. (1998) Environ. Sci. Technol. 32, 2410Rashid, M.A. (1985) Geochemistry of Marine Humic

Compounds, Springer-Verlag, NY, NY, 300 pages