N cycling in the world’s oceans

Nitrogen

• N is an essential nutrient for all living organisms (nucleic acids and amino acids)

• N has many oxidation states, which makes speciation and redox chemistry very interesting

• NH4+ is preferred N nutrient

Marine N

Non-bioavailableN2O 200 Tg N (+1)

N2 2.2*107 Tg N (0)

Bioavailable/Fixed (oxidation state) NO3

- 5.7*105 Tg N (+5)

NO2- 500 Tg N (+3)

NH4+ 7.0*103 Tg N (-3)

Organic N 5.3*105 Tg N (-3)

Libes, 1992

NitrateNitriteAmmonia

Marine Reservoir: 6.3*105 Tg N

Sources: 287 Tg N/yr

Atmospheric deposition: 86 Tg N/yr

N2 fixation: 125 Tg N/yr

River Input: 76 Tg N/yr

Codispoti et al. (2001)

Marine Fixed N Budget



Sinks: 482 Tg N/yr

Water Column denitrification:

150 Tg N/yr


N2O loss: 6 Tg N/yr


Sedimentation: 25 Tg N/yr

Benthic denitrification: 300 Tg N/yr

Organic N export: 1 Tg N/yr


Codispoti et al. (2001)




Sinks: 482 Tg N/yr

Water Column denitrification:

150 Tg N/yr


N2O loss: 6 Tg N/yr


Sedimentation: 25 Tg N/yr

Benthic denitrification: 300 Tg N/yr

Organic N export: 1 Tg N/yr


Codispoti et al. (2001)Hypothetical Fixed N Evolution

-2.E+05

0.E+00

2.E+05

4.E+05

6.E+05

8.E+05

0 500 1000 1500 2000 2500 3000 3500

Time (years)

Fixe

d N

(Tg)


Oceanic Nitrogen Budget Estimates

Georgia Tech Biological Oceanography

N Budget Terms(Tg N y-1)

1970(Delwiche)

1979(Liu)

1985(Codispoti &Christensen)

1997(Gruber &Sarmiento)

2001(Codispoti

et al.)

Inputsatmospheric 4.1 49 40 15 56runoff 30 17 25 41 41N2-fixation 10 30 25 125 125Total Inputs 44.1 96 90 181 222

Outputspelagic denitrification 40 50 60 85 150sedimentary denitrification 0 10 60 85 300burial & other 0.2 36 38 19 32Total Outputs 40.2 96 158 189 482


N* Distribution Shows Interplay Between N2-Fixation and Denitrification

N* = 0.87( [NO3-] - 16[PO4

3-] + 2.9) (Gruber & Sarmiento 1997)

Trichodesmium: The Usual Suspect• Diazotrophs, including Trichodesmium, are broadly distributed

in nutrient poor oceanic waters, but their contribution to the marine N budget remains poorly constrained.


Trichodesmium puffs (above) and tufts (right).Photos by Hans Paerl.

Trichodesmium blooms from aboard ship (left) and from space (below).


Major Biological Transformations of Nitrogen

(Inspired by Codispoti 2001and Liu 1979)

NO3

Chlorophyll

Largedetritus

Organic matter

N2 NH4 NO3

Water column

SedimentSediment

Phytoplankton

NH4

Mineralization

Uptake

Nitrification

Nitrification

Grazing

Mortality

Zooplankton

Susp.particles

Aerobic mineralizationAerobic mineralizationDenitrificationDenitrification

N2

Fixation

Mix Layer depth

Oceanic N Cycle Schematic

NH4+

New vs. Regenerated Production

BiologicalPump

Respiration ΔG° (kJ/mol) -119

Denitrification-113

MnO2 reduction

-96.9

Fe oxide reduction

-46.7Sulfate reduction

-20.5Methanogenesis

-17.728

148

124

1 COCHOCH

OHCOOOCH 241

241

241

241

OHNCOHNOOCH 221

2101

241

51

351

241

OHCOFeHOHFeOCH 2411

2412

3241 2)(

OHCOHSHSOOCH 241

241

81

812

481

241

OHMnCOHMnOOCH 2432

21

241

281

241

Organic Matter Oxidation Sequence Morel & Herring, 1993

Beggiatoa Mat Overview


Beggiatoa Mat


Alternative pathways to N2

OHCONHNOOCH 22232 752445

223

422 225 OOHNHOHN

HOHNOONH 22 2324 OHNNONH 2224 2

HOHNONH 223

221

243

4

OHNMnHNHMnO 222

42 63423

Nitrification Anammox

OLAND

MnO2 Reduction

Microbially mediated

Chemical Reactions

Heterotrophic Denitrification

Nitrogen Fixation

OHNOMnHNHMnO 232

42 5464

HNMnOOHNOMn )solid( 85425 22232

Mn2+ Oxidation

Microbial Community Processes


Microbial Community Model(mm - cm scale)

OrganicMatter

NH4+

NO3–

N2

O2

Assimilation

MnO2

MnO2

Mn2+ Fe2+


Alternative Pathways to N2

AmmonificationOrganicMatter NH4+

N2

NO3–+V

+III

+IV

+I+II

0

-I

-II

-III

NO2–NO2–

N2

Surface Nutrient Distribution

Data: eWOCE. Plot prepared with ODV

N cycling in the world’s oceans

Documents

Transcript of N cycling in the world’s oceans