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Nitrate Dynamics at ALOHA and K2

Nitrate Dynamics at ALOHA and K2

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Nitrate Dynamics at ALOHA and K2

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  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 d15N and d18O 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 d15N and d18O analysis • Microbial community analysis: Nitrifying and denitrifying bacteria • Free-living vs. particle attached

  3. What we can learn from NO3- isotopes? • Supply of N to the surface: NO3-, N2? • N export and remineralization • N cycling/turnover Nitrogen fixation N Norg Assimilation N NH4+ O N NO3- Denitrification Nitrification O O

  4. Subarctic Front Map of Surface Nitrate

  5. Comparison of Basic Chemical and Physical Parameters T O2  S NO3- Si ALOHA = Blue K2 = Red

  6. Nitrate Isotopic Profiles • 10 profiles from ALOHA • 6 profiles from K2 • Analyzed for d15N and d18O using “denitrifier method” • Allows isotopic analysis of previously inaccessible pools of NO3-

  7. The denitrifier method Pseudomonas aureofaciens Inject NO3- or NO2- sample or Pseudomonas chlororaphis Denitrification takes place NO3- NO2- NO N2O N2 Analyze N2O isotopes N2O (g) Sigman et al., 2001. Analytical Chemistry: 15N-NO3- Casciotti et al., 2002. Analytical Chemistry: 18O-NO3-

  8. K2: T, S, NO3-, and PO4-

  9. d15N and d18O-NO3- at K2

  10. Temperature vs. d15N and d18O

  11. d15N and d18O vs. density Thorium excess

  12. d15N and d18O-NO3- at K2

  13. d15N-NO3- at K2 EZD MLD PN T [NO3-] 15NNO3

  14. Fluxes of N at Station K2 NO3- NH4+ Export Remineralization flux NO3- PN Flux, d15N 150 m trap Remineralization flux PN Flux, d15N 300 m trap Remineralization flux PN Flux, d15N 500 m trap

  15. d15N vs. d18O Close-up, station 73 All data

  16. N and O isotope dynamics in nitrate Assimilation d18O-NO3- Initial NO3- d15N-NO3-

  17. N and O isotope dynamics in nitrate Assimilation d18O-NO3- Partially consumed NO3- Produced PN d15N-NO3-

  18. N and O isotope dynamics in nitrate Assimilation d18O-NO3- Partially consumed NO3- Produced PN d15N-NO3-

  19. d15N vs. d18O Close-up, station 73 All data

  20. ALOHA T, S, NO3-, and PO4-

  21. d15N and d18O-NO3- at ALOHA

  22. Fluxes of N at Station ALOHA N2 NO3- NH4+ Export Remineralization flux PN Flux, d15N 150 m trap Remineralization flux PN Flux, d15N 300 m trap Remineralization flux PN Flux, d15N 500 m trap

  23. ALOHA d15N vs. d18O

  24. N and O isotope dynamics in nitrate Fully consumed NO3- Assimilation d18O-NO3- Produced PN d15N-NO3-

  25. N and O isotope dynamics in nitrate Fully consumed NO3- Assimilation d18O-NO3- N2 fixation PN d15N-NO3-

  26. ALOHA d15N vs. d18O

  27. d15N and d18O-NO3- at ALOHA

  28. d15N and d18O-NO3- at ALOHA

  29. d15N and d18O-NO3- at K2 EZD MLD PN Real data from K2 cast 24 15NNO3