1. Nitrate Dynamics at ALOHA and K2 Karen Casciotti Woods Hole Oceanographic Institution Department of Marine Chemistry and Geochemistry

2. VERTIGO Experiments ALOHA 2004 Nitrate isotopic profiles  Coupled  15 N and  18 O analysis Rates of microbial activity  Nitrification Rates  Whole water samples and MULVFS particles Microbial community analysis: free-living vs. particle attached  Nitrifying and denitrifying bacteria  Suspended particles (MULVFS)  Sinking particles (CLAP traps Hg vs. Formalin preservation)  Hand-picked squiggles, tufts, and puffs K2 2005 Nitrate isotopic profiles  Coupled  15 N and  18 O analysis Microbial community analysis: Nitrifying and denitrifying bacteria  Free-living vs. particle attached

3. What we can learn from NO 3 - isotopes? Supply of N to the surface: NO 3 -, N 2 ? N export and remineralization N cycling/turnover Nitrification N org N N NH 4 + Assimilation Nitrogen fixation Denitrification O O NO 3 - N O

4. Map of Surface Nitrate Subarctic Front

5. Comparison of Basic Chemical and Physical Parameters T S  O2O2 NO 3 - Si ALOHA = Blue K2 = Red

6. Nitrate Isotopic Profiles 10 profiles from ALOHA 6 profiles from K2 Analyzed for  15 N and  18 O using “denitrifier method”  Allows isotopic analysis of previously inaccessible pools of NO 3 -

7. Pseudomonas aureofaciens Pseudomonas chlororaphis or Sigman et al., 2001. Analytical Chemistry: 15 N-NO 3 - Casciotti et al., 2002. Analytical Chemistry: 18 O-NO 3 - Inject NO 3 - or NO 2 - sample N 2 O (g) Analyze N 2 O isotopes NO 3 - NO 2 - NON 2 ON 2 Denitrification takes place The denitrifier method

8. K2: T, S, NO 3 -, and PO 4 -

9.  15 N and  18 O-NO 3 - at K2

10. Temperature vs. d15N and d18O

11. d15N and d18O vs. density Thorium excess

12.  15 N and  18 O-NO 3 - at K2

13.  15 N-NO 3 - at K2 T 15 N NO3 [NO 3 - ] MLD EZD PN

14. Fluxes of N at Station K2 300 m trap 150 m trap 500 m trap Export Remineralization flux PN Flux,  15 N NO 3 - NH 4 + Remineralization flux

15.  15 N vs.  18 O All data Close-up, station 73

16. Assimilation  15 N-NO 3 -  18 O-NO 3 - Initial NO 3 - N and O isotope dynamics in nitrate

17. Assimilation  15 N-NO 3 -  18 O-NO 3 - Partially consumed NO 3 - Produced PN N and O isotope dynamics in nitrate

18. Assimilation  15 N-NO 3 -  18 O-NO 3 - Partially consumed NO 3 - Produced PN N and O isotope dynamics in nitrate

19.  15 N vs.  18 O All data Close-up, station 73

20. ALOHA T, S, NO 3 -, and PO 4 -

21.  15 N and  18 O-NO 3 - at ALOHA

22. Fluxes of N at Station ALOHA 300 m trap 150 m trap 500 m trap Export Remineralization flux PN Flux,  15 N NO 3 - NH 4 + Remineralization flux N2N2

23. ALOHA  15 N vs.  18 O

24. Assimilation  15 N-NO 3 -  18 O-NO 3 - Fully consumed NO 3 - Produced PN N and O isotope dynamics in nitrate

25. Assimilation  15 N-NO 3 -  18 O-NO 3 - Fully consumed NO 3 - PN N and O isotope dynamics in nitrate N 2 fixation

26. ALOHA  15 N vs.  18 O

27.  15 N and  18 O-NO 3 - at ALOHA

29.  15 N and  18 O-NO 3 - at K2 15 N NO3 MLD EZD PN Real data from K2 cast 24