1. 1 Isotopic Tracers of Source Material and Food Webs The bulk of the applications of isotopic measurements is to identify and, sometimes, quantify the input of material to a reservoir. The reservoir can be an organism (e.g., food input or diet), sediments (e.g., input of organic matter), the atmosphere (e.g., input of methane or CO 2 ) etc. All the light isotopes (C, H, O, N and S) have applications in these studies.

2. 2 Using Isotopes as Tracers Utility of approach depends on the magnitude of the isotopic separation of sources and the variability in their isotopic composition. Generally, the more isotopes (and other compositional characteristics) applied to the problem, the more tightly constrained are the sources and more information gained. The approach is sometimes (often?) deceptively simple and, as a result, misleading.

3. 3 Two Sources

4. 4  13 C of OM in Sediments of Hood Canal, WA Three sediment cores collected during a student cruise in Hood Canal in 1999.  13 C (‰) % Marine

5. 5 Considerations Variability -spatial: between core and down core -temporal: have  13 C signatures changed? Degradation -Diagenetic changes in  13 C of sediments Complementary Measurements -compound specific  13 C measurements -chemical composition (C/N, lignins,) -other isotopes (  15 N )

6. 6 Offshore trends in the  13 C and OC:SA of OM in sediments on a river delta River Delta

7. 7 Isotopic Composition of Major Sources and Sinks of Atmospheric CH 4 Three categories: -Bacterial -Biomass Burning -Fossil fuel

8. 8 Isotopic Composition of Major Sources and Sinks of Atmospheric CH 4

9. 9 Rivers in the Amazon Basin

10. 10  13 C and Chemical Composition of Organic Matter in Rivers in the Amazon Basin Λ represents the lignin/carbon for organic material. Lignins are produced only by vascular plants. Coarse and fine suspended OM were analyzed. The inset indicates same characteristics for possible source material (leaves, wood, grasses)

11. 11 Uncertainty in Method  13 C  15 N or C/N or lignin/C  13 C  15 N or C/N or lignin/C

12. 12  13 C Dietary Effects You are what you eat.

13. 13  13 C of Organic Compounds

14. 14  13 C of Offshore Food Web

15. 15 Trophic Level Isotope Changes +3 ‰ Change

16. 16  34 S Variations Std= Canyon Diablo meteorite

17. 17 Application of  34 S to Food Webs Studies The basis of  34 S application is the distinctly different isotopic composition of oxidized (sulfate) versus reduced (sulfide) sulfur compounds. Bacteria reduce sulfate to sulfide under anaerobic conditions 2CH 2 O + SO 4 =  2HCO 3 - + H 2 S Bacteria oxidize sulfide to sulfate under aerobic conditions H 2 S + 2O 2  SO 4 = + 2H +

18. 18 KIEs during Sulfate and Sulfite Reduction (Lab Studies)  = -10 to –50 ‰  = 0 to –20 ‰

19. 19 KIE During Sulfate Reduction (field studies)  = -40 to –60 ‰  = –60 ‰)

20. 20 Field data indicate a larger (-30 to -70 ‰) depletion in 34 S of sulfides, relative to sulfate, than in culture studies (0 to –40 ‰). Canfield and Teske (1996)

21. 21  34 S and  13 C as tracers of Sulfur and Carbon Cycles F SO4 + F S= = 1 F SO4 *  34 S SO4 + F S= *  34 S S= = 0 ‰ (std) F SO4 *  34 S SO4 + F S= * (  34 S SO4 – 50 ‰) = 0 ‰  34 S SO4 = 30 ‰, F SO4 =40%  34 S SO4 = 10 ‰, F SO4 =80% Low  34 S SO4 and  13 C CO3 during Phanerozoic could be a result of high marine photosynthesis rates(?).

22. 22  13 C of a Tracer of Animals Diet (C3 vs C4 plants)

23. 23  13 C of Suspended POM in Rivers The  13 C of POM in rivers depends primarily on proportion of drainage basin in (C4) grasslands. Interestingly, the  13 C of POM discharged by Mississippi R. at –20 ‰ is similar to marine POM.

24. 24  13 C of Emu egg shells as proxy for climate

25. 25  13 C as tracer of paleo C4 grass abundance

26. 26  13 C as a tracer of seagrass diet source

27. 27  15 N as Trophic Level Indicator and  13 C as Diet Source

28. 28  15 N as Trophic Level Indicator  15 N (‰) l Correlation between Hg accumulation and  15 N (trophic level) in trout

29. 29  15 N as Tracer of Nitrogen Input from Salmon

30. 30  15 N as Tracer of Historic Salmon Spawning l

31. 31  15 N as Tracer of Historic Salmon Spawning

32. 32 Using  13 C,  15 N and  34 S to identify food web in salt marsh

33. 33 Histograms of  13 C,  15 N and  34 S for Consumers

34. 34  13 C and  34 S as Tracers of Diets for Seabirds