OCN 623 Chemical Oceanography

Transcription

1 OCN 623 Chemical Oceanography Reading: Libes, Chapters 22 & 23 (much detail on subject) Note: You can skim the details on compound classes (22.4) Operational definitions! 1

2 POM 2

3 Organic compounds display a range of polarities: CH 4 - methane (non-polar) CH 3 COOH - acetate (polar) C 16 - n-hexadecane (non-polar) CH 3 -(CH 2 ) 16 -COOH - stearate (polar carboxyl group + non-polar wax = "fatty acid") Fatty acids in water tend to form micelles: Polar (acidic) head Non-polar (waxy) body Increasing polarity 3

4 Pre-industrial coastal ocean organic C cycle DOC & POC transported from land & formed in situ POC 50% reactive, 50% refractory 4

5 Carbon: not just for the coastal & photic zone anymore

6 3. Dissolved organic matter (DOM) a. Dissolved organic carbon (DOC) Oceanic concentrations = µg-c/l to mg-c/l Turnover time: days to centuries, depending on compound Very fast during blooms, when large amounts of DOC are excreted Typical upper ocean DOC turnover time: 3-40 days. b. Dissolved organic nitrogen (DON) Oceanic concentrations = µg-n/l Much shorter turnover time c. Dissolved organic phosphorus (DOP) Oceanic concentrations = ng-p/l to µg-p/l Presumably very fast turnover time Note: If you are using mass/vol units, be sure you specify if you mean mass of atoms or mass of molecules! 6

7 myriad of forms that organic molecules exhibit in the environment More complexity: Multiple bonds, Stereochemical isomers, additional elements (N, O, S, P) Isotopes 7

8 DOC is messy Vast structural diversity of organic matter in marine and terrestrial systems poses a significant challenge to geochemists trying to identify & quantify individual components Requires many different analytical procedures, many require breaking down macromolecules before separating by chromatography Dan Repeta (WHOI), Kai Hinrichs (Bremen), Fabien Kenig (UIC), Craig Carlson (UCSB) Characterized by functional groups More polar, larger, molecules have higher boiling/melting points O & N impart polarity = solubility Dissociated or protonated H & O within alcohols, phenols, carboxylic acids, amines are interchangeable; not C & N 8

9 Learn a little about a lot or a lot about a little? Separation & identification of certain compound classes, Usually only a sm % of TOC, though 9

10 C, H, O, N, S CHN analyzers Differing classes, Also different Org C sources, e.g. terrestrial vs marine Compounds rich in H & low in O (lipids) have a high O 2 demand for complete respiration 10

11 DOC in this case: Passes through Whatman GF/F filter (0.7 um) Downward DOC flux a significant fraction of OC flux Mixed layer high DOC Subsurface layer steep DOC gradient Deep water Low and constant DOC conc. Seafloor 11

12 Filter water first thru a 0.2 µm filter to obtain DOC, then thru a series of ultrafilters to measure colloidal organic carbon: COC 10 = 10 kda µm (>200 L, 8 h) COC 3 = 3 kda µm (>200 L, 8 h) COC 1 = 1 kda µm (1000 L, 12 h) 1 Dalton = mass of 1 hydrogen atom = 1.67 x g 10 kda 0.2 um 3-10 kda 1-3 kda (Guo et al., 1995) 1. Autochthonous vs. Allochthonous organic matter (locally produced vs. imported) Greek roots: "auto" = self "allo" = other "chthonous" = earth, ground 2. In general, the major source of open ocean OM is planktonic primary producers (autochthonous) Most OM exported from coastal waters (allochthonous) is consumed in stratified continental shelf waters during the summer 12

13 Seawater bulk DOM chemical composition is not consistent with riverine origin Most evidence suggests that seawater DOM is largely autochtonous rather than being allochtonous 13

14 3. OM abundance in the open ocean is controlled by grazing: ~85% of primary production is recycled through consumers ~15% is released from primary producers by extracellular release This extracellular release supplies ~50% of microbial growth requirements 5. Humic materials Part of colored dissolved organic matter (CDOM) Gelbstoffe Mostly terrestrial in origin (e.g., brown rivers) Product of random polymerization Refractory Quickly removed from seawater by poorly understood processes CO CO 2 10? 14

15 Adsorption of UV and visible light by CDOM: Controls UV penetration Impacts phytoplankton and other microbial activity A primary reactant in the photoproduction of CO 2, CO, H 2 O 2, OCS (carbonyl sulfide) Can affect remote observations of ocean chlorophyll and primary production Coastal regions: Mostly terrestrial humic and fulvic acids (from plant-matter breakdown) from rivers and runoff CDOM decreases with distance from coast, as does DOM Open ocean: Composition in open ocean is largely unknown <5% from terrestrial sources DOM from microbial excretion / lysis must be altered to become CDOM Summertime bleaching of CDOM -- lowers CDOM conc but has negligible effect on DOM conc Significant variations in CDOM concs occur in the upper ocean over seasonal-to-interannual timescales CDOM and DOM concs vary inversely over large space scales Nelson, N.B., D.A. Siegel, Chromophoric DOM in the Open Ocean. In: Biogeochemistry of Marine Dissolved Organic Matter, D.A. Hansell, C.A. Carlson (eds.), Academic Press,

16 Absorption spectra: a chl - chlorophyll absorbance a cdom - CDOM absorbance a w - pure water absorbance Two main processes: H 2 O 2 (hydrogen peroxide) production: O 2 + 2e - + 2H + + hυ H 2 O 2 DOM oxidation: DOM + O 2 + hυ CO 2 + altered-dom Similar rate of O 2 consumption by each process 16

17 17

18 Pond Gulf of Mexico Moderately productive sw Sargasso Sea 18

19 Back to consideration for composition Back to consideration for composition 19

20 Particulate Organic Matter Fluxes Primary Production Rate Recycling Early Diagenesis Fig 23.5 in text 20

21 Biomarkers relatively unchanged during sedimentation and diagenesis 21

22 E.g., difficulty of uptake or degradation of specific compounds E.g., intercalation into clay minerals Mayer 2004 A succession of preservation methods as the OM ages 22

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