N cycling in the worlds oceans

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N cycling in the worlds oceans
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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

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Marine N

• Bioavailable/Fixed (oxidation state)
• NO3- 5.7105 Tg N (5)
• NO2- 500 Tg N (3)
• NH4 7.0103 Tg N (-3)
• Organic N 5.3105 Tg N (-3)

Libes, 1992

• Non-bioavailable
• N2O 200 Tg N (1)
• N2 2.2107 Tg N (0)

Nitrate
Nitrite
Ammonia
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Marine Fixed N Budget
Codispoti et al. (2001)
Marine Reservoir 6.3105 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
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Marine Fixed N Budget
Codispoti et al. (2001)
Marine Reservoir 6.3105 Tg N Sources 287 Tg
N/yr Sinks 482 Tg N/yr

Atmospheric deposition 86 Tg N/yr
N2 fixation 125 Tg N/yr
N2O loss 6 Tg N/yr
Water Column denitrification 150 Tg N/yr
River Input 76 Tg N/yr
Organic N export 1 Tg N/yr
Benthic denitrification 300 Tg N/yr
Sedimentation 25 Tg N/yr
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Marine Fixed N Budget
Codispoti et al. (2001)
Marine Reservoir 6.3105 Tg N Sources 287 Tg
N/yr Sinks 482 Tg N/yr

Atmospheric deposition 86 Tg N/yr
N2 fixation 125 Tg N/yr
N2O loss 6 Tg N/yr
Water Column denitrification 150 Tg N/yr
River Input 76 Tg N/yr
Organic N export 1 Tg N/yr
Benthic denitrification 300 Tg N/yr
Sedimentation 25 Tg N/yr
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Oceanic Nitrogen Budget Estimates
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N Distribution Shows Interplay Between
N2-Fixation and Denitrification
N 0.87( NO3- - 16PO43- 2.9) (Gruber
Sarmiento 1997)
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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 blooms from aboard ship (left) and
from space (below).
Trichodesmium puffs (above) and tufts
(right). Photos by Hans Paerl.
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Major Biological Transformations of Nitrogen
(Inspired by Codispoti 2001and Liu 1979)
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Oceanic N Cycle Schematic
Fixation
N2
Nitrification
Mineralization
NH4
NO3
Uptake
Phytoplankton
Grazing
Mix Layer depth
Chlorophyll
Zooplankton
Mortality
Large detritus
Water column
Susp. particles
Nitrification
N2
NH4
NO3
Denitrification
Aerobic mineralization
Organic matter
Sediment
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New vs. Regenerated Production
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Organic Matter Oxidation Sequence Morel
Herring, 1993
Respiration
?G (kJ/mol)

-119 Denitrification
-113 MnO2 reduction -96.9
Fe oxide reduction -46.7 Sulfate
reduction -20.5 Methanogenesis
-17.7
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Beggiatoa Mat Overview
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Beggiatoa Mat
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Alternative pathways to N2
Microbially mediated
Nitrification
Anammox
OLAND
Heterotrophic Denitrification
Nitrogen Fixation
Chemical Reactions
MnO2 Reduction
Mn2 Oxidation
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Microbial Community Processes
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Alternative Pathways to N2
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Surface Nutrient Distribution
Data eWOCE. Plot prepared with ODV