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
Marine Reservoir: 6.3*105 Tg N
Sources: 287 Tg N/yr
Sinks: 482 Tg N/yr
Water Column denitrification:
150 Tg N/yr
Atmospheric deposition: 86 Tg N/yr
N2O loss: 6 Tg N/yr
N2 fixation: 125 Tg N/yr
Sedimentation: 25 Tg N/yr
Benthic denitrification: 300 Tg N/yr
Organic N export: 1 Tg N/yr
River Input: 76 Tg N/yr
Codispoti et al. (2001)
Marine Fixed N Budget
Marine Reservoir: 6.3*105 Tg N
Sources: 287 Tg N/yr
Sinks: 482 Tg N/yr
Water Column denitrification:
150 Tg N/yr
Atmospheric deposition: 86 Tg N/yr
N2O loss: 6 Tg N/yr
N2 fixation: 125 Tg N/yr
Sedimentation: 25 Tg N/yr
Benthic denitrification: 300 Tg N/yr
Organic N export: 1 Tg N/yr
River Input: 76 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)
Marine Fixed N Budget
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
Georgia Tech Biological Oceanography
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.
Georgia Tech Biological Oceanography
Trichodesmium puffs (above) and tufts (right).Photos by Hans Paerl.
Trichodesmium blooms from aboard ship (left) and from space (below).
Georgia Tech Biological Oceanography
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
Georgia Tech Biological Oceanography
Beggiatoa Mat
Georgia Tech Biological Oceanography
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
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Microbial Community Model(mm - cm scale)
OrganicMatter
NH4+
NO3–
N2
O2
Assimilation
MnO2
MnO2
Mn2+ Fe2+
Georgia Tech Biological Oceanography
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
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