Post on 05-Jan-2016
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
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Nutrient Cycles• Nutrient limitation
– N sources
• N Cycle– Budget
– N2 Fixation
• Links to the C Cycle
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPMKrebs, Fig. 25.08
Marine N Limitation (Ryther & Dunstan 1971)
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
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)
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
Surface Nutrient Distribution
Data: eWOCE. Plot prepared with ODV
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
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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
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
N-Cycle as a Redox Web
(Modified from Codispoti 2001and Liu 1979)
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
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)
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!
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
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
North Atlantic Nutrient Ratios
Data: eWOCE. Plot prepared with ODV
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)
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
Diazotroph Diversity
(Images courtesy R. Foster)
(Zehr et al., 2001. Nature 412)
?
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
KM0703: 11 Mar – 15 Apr 2007
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM
KM0703 Stns. 4 - 10 Group A Abundance
(Moisander et al., in prep)
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
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KM0703 Areal N2-Fixation RatesAreal Rate ( µmole m-2 d-1)
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPMGruber & Galloway, 2008, Nature
Biogeochemical “Gears”Fluxes in Tg N y-1
EAS 4300 Guest Lecture
Georgia Tech Biological Oceanography
JPM(inspired by Gruber 2004)
N-Cycle Feedbacks