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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
Nutrient Cycles• Nutrient limitation
– N sources
• N Cycle– Budget
– N2 Fixation
• Links to the C Cycle
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPMKrebs, Fig. 25.08
Marine N Limitation (Ryther & Dunstan 1971)
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
Anthropogenic N Loading
Globally, about 20% of anthropogenic N input on land is exported in rivers.
Krebs, Fig. 27.18
Crouzet et al. 1999, EEA
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
EutrophicationN inputs to coastal waters often promote algal blooms
Cyanobacterial bloom in the Baltic (www.eea.europa.eu)
Dinoflagellate bloom off La Jolla (Photo: P. Franks, SIO) Agricultural runoff and blooms (Beman et al. 2005)
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
Surface Nutrient Distribution
Data: eWOCE. Plot prepared with ODV
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
Upper Water Column: NPSG
Krebs, Fig. 25.07
Thermal stratification reduces nutrient supply– Thermocline inhibits mixing
– Nutrients stripped from surface layer by biota
– Production is nutrient (N) limited over much of the open ocean
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
N-Cycle as a Redox Web
(Modified from Codispoti 2001and Liu 1979)
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
Marine NFix: >135
land: < 200ocean: > 400?
Terr Nfix: 140
Lightning: 3
20
> 80
Crouzet et al. 1999, EEA
Pool sizes (Tg N)Atmosphere: 3.9 x 109
Terr. Biota: 13,000Soil organics: 300,000
Marine NO3-: 570,000
Marine biota: 500
Global N Cycle CartoonFluxes in Tg N y-1
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
Oceanic Nitrogen Budget Estimates
N Budget Terms (Tg N y-1 = 1012 g N y-1)
1970 (Delwiche)
1979 (Liu)
1985 (Codispoti &
Christensen)
1997 (Gruber &
Sarmiento)
2007 (Codispoti)
Inputs atmospheric 4.1 49 40 15 30 runoff 30 17 25 41 78 N2-fixation 10 30 25 125 135+++ Total Inputs 44.1 96 90 181
243
Outputs pelagic denitrification 40 50 60 85 150++ sedimentary denitrification 0 10 60 85 300+ burial & other 0.2 36 38 19 25 Total Outputs
(net balance) 40.2 96 158
(-68) 189 475
(-232)
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
Who Cares?• Broad reaches of the ocean are N-limited.
– Recycling of N within the water column supports biological production, but…
– Injection of new N into the upper water column is required to support export production.
• The N and C cycles are tightly coupled through biological production of organic matter (C:N ≈ 7).
• N2-fixation plays a key role in regulating the global C cycle but we still don’t how much N2-fixation is occurring in the ocean, who’s doing it, and where!
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
NH4+
New vs. Regenerated Production
modified from http://www.up.ethz.ch/research/nitrogen_cycle/index
BiologicalPump
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
North Atlantic Nutrient Ratios
Data: eWOCE. Plot prepared with ODV
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
N* Distributions Reflect the Impact of N2-Fixation & Denitrification
Data: eWOCE. Plot prepared with ODV
N* = 0.87( [NO3-] - 16[PO4
3-] + 2.9) (Gruber & Sarmiento 1999)
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
Diazotroph Diversity
(Images courtesy R. Foster)
(Zehr et al., 2001. Nature 412)
?
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
KM0703: 11 Mar – 15 Apr 2007
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
KM0703 Stns. 4 - 10 Group A Abundance
(Moisander et al., in prep)
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
KM0703 Areal N2-Fixation RatesAreal Rate ( µmole m-2 d-1)
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPMGruber & Galloway, 2008, Nature
Biogeochemical “Gears”Fluxes in Tg N y-1
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EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM(inspired by Gruber 2004)
N-Cycle Feedbacks