eas 4300 guest lecture georgia tech biological oceanography jpm nutrient cycles nutrient limitation...

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



JPMKrebs, Fig. 25.08

Marine N Limitation (Ryther & Dunstan 1971)



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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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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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Surface Nutrient Distribution

Data: eWOCE. Plot prepared with ODV



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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



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N-Cycle as a Redox Web

(Modified from Codispoti 2001and Liu 1979)



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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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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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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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NH4+

New vs. Regenerated Production

modified from http://www.up.ethz.ch/research/nitrogen_cycle/index

BiologicalPump



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North Atlantic Nutrient Ratios




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N* Distributions Reflect the Impact of N2-Fixation & Denitrification


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

3-] + 2.9) (Gruber & Sarmiento 1999)



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Diazotroph Diversity

(Images courtesy R. Foster)

(Zehr et al., 2001. Nature 412)

?



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KM0703: 11 Mar – 15 Apr 2007



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KM0703 Stns. 4 - 10 Group A Abundance

(Moisander et al., in prep)



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KM0703 Areal N2-Fixation RatesAreal Rate ( µmole m-2 d-1)



JPMGruber & Galloway, 2008, Nature

Biogeochemical “Gears”Fluxes in Tg N y-1



JPM(inspired by Gruber 2004)

N-Cycle Feedbacks

eas 4300 guest lecture georgia tech biological oceanography jpm nutrient cycles nutrient limitation...

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