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

Transcription

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

2 VERTIGO 24 Experiments Nitrate isotopic profiles Coupled δ 15 N and δ 18 O analysis Rates of microbial activity Nitrification Rates Whole water samples and MULVFS particles Microbial community analysis: freeliving vs. particle attached Nitrifying and denitrifying bacteria Suspended particles (MULVFS) Sinking particles (CLAP traps Hg vs. Formalin preservation) Handpicked squiggles, tufts, and puffs

3 VERTIGO 25 Experiments Nitrate isotopic profiles Coupled δ 15 N and δ 18 O analysis Microbial community analysis: Nitrifying and denitrifying bacteria Freeliving vs. particle attached

4 Eppley and Peterson, 1979: Export Production and the Biological Pump N 2 fixation CO 2 Atmospheric deposition New Production NO 3 NH 4 CO 2 CO 2 Phytoplankton Zooplankton Regenerated Production NH 4 DON, DOC CO 2 Bacteria Euphotic zone Export Aphotic zone Dead organic production matter

5 Map of Surface Nitrate Subarctic Front

6 Comparison of Basic Chemical and Physical Parameters T S σ θ O 2 Si NO 3 ALOHA = Blue K2 = Red

7 What we can learn from NO 3 isotopes? Supply of N to the surface N cycling/turnover N export and remineralization

8 Rayleigh Fractionation δ 15 NO 3 15 δ15 NO 3 1 δ 15 NPN inst ε 5 ε ε δ 15 NPN accum f = [NO 3 ]/[NO3initial substrate]

9 N and O isotopic fractionation during N cycling Nitrogen fixation NH 4 Nitrification O 2, H 2 O N 2 N org Assimilation NO 3 N org H 2 O Denitrification N 2 H 2 O δ 18 ONO 3 NO 3 N 2 fix. Assimilation Deep Denitrification Nitrification δ 15 NNO 3

10 Nitrate Isotopic Profiles 1 profiles from ALOHA 6 profiles from K2 Analyzed for δ 15 N and δ 18 O using denitrifier method Allows isotopic analysis of previously inaccessible pools of NO 3

11 The denitrifier method Pseudomonas aureofaciens or Pseudomonas chlororaphis Inject NO 3 or NO 2 sample NO 3 NO 2 NO N 2 O N 2 Denitrification takes place N 2 O (g) Analyze N 2 O isotopes Sigman et al., 21. Analytical Chemistry: 15 NNO 3 Casciotti et al., 22. Analytical Chemistry: 18 ONO 3

12 K2: T, S, NO 3, and PO 4 Depth (m) Sigma Theta Temperature (¼C) Salinity (PSU) Depth (m) Nitrate, cast 24 Nitrate, cast 73 Nitrate, cast 27 Nitrate, cast 5 Nitrate, cast 72 Phoshpate, cast 24 Phosphate, cast Phosphate (µm) 4 Nitrate (µm)

13 δ 15 N and δ 18 ONO 3 at K2 2 4 δ 18 ONO δ 15 NNO Depth (m) 15 Depth (m)

14 Nitrate consumption and mixing 12 δ 15 NNO 3 Cast 24 δ 15 NNO 3 Cast 73 1 δ 15 NNO 3 Cast 27 δ 15 NNO 3 Cast 5 δ 15 NNO 3 Cast 72 and δ 15 NNO δ 15 NNO 3 Closed system model δ 15 NNO 3 δ 18 ONO δ 18 ONO 3 Cast 24 δ 18 ONO 3 Cast 73 δ 18 ONO 3 Cast 27 δ 18 ONO 3 Cast 5 δ 18 ONO 3 Cast 72 δ 18 ONO 3 δ 18 ONO 3 Closed system model ln [NO 3 ]

15 Isotope mixing Fractionation alone Fractionation and mixing δ 15 NO 3 ε δ 15 NO 3 ε ln[no 3 ] ln[no 3 ]

16 Nitrate consumption and mixing and δ 15 NNO 3 δ 18 ONO Upper 5 m T min Below 2 m δ 15 NNO 3 Cast 24 δ 15 NNO 3 Cast 73 δ 15 NNO 3 Cast 27 δ 15 NNO 3 Cast 5 δ 15 NNO 3 Cast 72 δ 15 NNO 3 Closed system model δ 18 ONO 3 Cast 24 δ 18 ONO 3 Cast 73 δ 18 ONO 3 Cast 27 δ 18 ONO 3 Cast 5 δ 18 ONO 3 Cast 72 δ 18 ONO 3 Closed system model ln [NO 3 ] δ 15 NNO 3 δ 18 ONO 3

17 δ 15 N vs. δ 18 O 12 1 δ 18 ONO δ 15 N vs. δ 18 O, slope =1.11 ± δ 15 NNO

18 Fluxes of N at Station K2 Export Less Efficient Remineralization? 15 m trap 3 m trap PN Flux, δ 15 N Remineralization flux PN Flux, δ 15 N Remineralization flux 5 m trap PN Flux, δ 15 N

19 ALOHA T, S, NO 3, and PO 4 Temperature (C) Nitrate (µm) Depth (m) Depth (m) Sigma Theta (kg m 3 ) Salinity (PSU) Phosphate (µm)

20 δ 15 N and δ 18 ONO 3 at ALOHA 1 2 δ 18 ONO δ 15 NNO Depth (m) 15 Depth (m)

21 ALOHA ln[no 3 ] vs. δ 12 δ 18 ONO 3 δ 15 NNO 3 1 and δ 15 NNO 3 δ 18 ONO ln [NO 3 ] 3. 4.

22 ALOHA δ 15 N vs. δ 18 O

23 Interpretation 12 A. B. δ 18 ONO Surface Deep δ 18 ONO 3 N 2 fix. Assimilation Denitrification Thermocline Nitrification 4 8 δ 15 NNO 3 12 δ 15 NNO 3

24 N cycling at ALOHA N 2 fixation Export δ 15 NPN ~ 1.5 in summer 7 Efficient Remineralization 15 m trap 3 m trap PN Flux PN Flux Remineralization flux Remineralization flux PN Flux 5 m trap

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26 North Pacific Nitrate Section K2 ALOHA Subtropical Subpolar

27 Nitrification Rate Profiles On Board Collect water samples from niskin or resuspended particles from MULVFS Aliquot in replicate 25 ml polycarbonate bottles Spike with 15 NNO 3 (5 ) Subsample over 5 days, freeze samples On Shore Analyze nitrate concentration, δ 15 N, δ 18 O Calculate nitrate production by isotope dilution

28 Microbial Community Analysis N 2 O NO DNA extracted from MULFVS and trap samples, as well as handpicked plankton Ammoniaoxidizing bacterium N 2 O NOR NH 4 O 2 AMO HAO H NH 2 OH 2 O H 2 O NO NIR NO 2 PCR products obtained for amoa, haoa, and norb from a handful of samples.

29 Microbial community investigations Sample Description amoa haoa norb 4_1 MULVFS surface 3_2 MULVFS ~15 m 3_4 MULVFS ~3 m 4_5 MULVFS ~5 m 3_6 blank 21C NBST 15 m Hg 211C NBST 15 m Formalin 231C NBST 3 m Hg 232C NBST 3 m Formalin 252C NBST 5 m Hg 253C NBST 5 m Formalin 265C blank clap trap Squiggles Handpicked nd Tufts Handpicked nd Puffs Handpicked nd

30 North Pacific Surface Currents

31 Further context Vertigo ALOHA,K2 d15nno ALOHA26 ALOHA29 K2 K2 K2 KM45 KM45 2 PAPA DannyETNP 25 peru