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Nutrient Cycles

Georgia Institute of Technology. Biological Oceanography. Nutrient Cycles. Nutrient limitation N sources N Cycle Budget N 2 Fixation Links to the C Cycle. Marine N Limitation (Ryther & Dunstan 1971). Krebs, Fig. 25.08. Anthropogenic N Loading. Krebs, Fig. 27.18.

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Nutrient Cycles

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  1. Georgia Institute of Technology Biological Oceanography Nutrient Cycles • Nutrient limitation • N sources • N Cycle • Budget • N2 Fixation • Links to the C Cycle

  2. Marine N Limitation (Ryther & Dunstan 1971) Krebs, Fig. 25.08

  3. Anthropogenic N Loading Krebs, Fig. 27.18 Globally, about 20% of anthropogenic N input on land is exported in rivers. Crouzet et al. 1999, EEA

  4. Cyanobacterial bloom in the Baltic (www.eea.europa.eu) Eutrophication N inputs to coastal waters often promote algal blooms Agricultural runoff and blooms (Beman et al. 2005) Dinoflagellate bloom off La Jolla (Photo: P. Franks, SIO)

  5. Surface Nutrient Distribution Data: eWOCE. Plot prepared with ODV

  6. Upper Water Column: NPSG 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 Krebs, Fig. 25.07

  7. N-Cycle as a Redox Web (Modified from Codispoti 2001and Liu 1979)

  8. land: < 200 ocean: > 400? Lightning: 3 Terr Nfix: 140 > 80 20 Marine NFix: >135 Global N Cycle Cartoon Pool sizes (Tg N) Atmosphere: 3.9 x 109 Terr. Biota: 13,000 Soil organics: 300,000 Marine NO3-: 570,000 Marine biota: 500 Fluxes in Tg N y-1 Crouzet et al. 1999, EEA

  9. Oceanic Nitrogen Budget Estimates

  10. 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!

  11. Biological Pump NH4+ New vs. Regenerated Production modified from http://www.up.ethz.ch/research/nitrogen_cycle/index

  12. North Atlantic Nutrient Ratios Data: eWOCE. Plot prepared with ODV

  13. N* Distributions Reflect the Impact of N2-Fixation & Denitrification N* = 0.87( [NO3-] - 16[PO43-] + 2.9) (Gruber & Sarmiento 1999) Data: eWOCE. Plot prepared with ODV

  14. ? Diazotroph Diversity (Images courtesy R. Foster) (Zehr et al., 2001. Nature 412)

  15. KM0703: 11 Mar – 15 Apr 2007

  16. KM0703 Stns. 4 - 10 Group A Abundance (Moisander et al., in prep)

  17. KM0703 Areal N2-Fixation Rates Areal Rate ( µmole m-2 d-1)

  18. Fluxes in Tg N y-1 Biogeochemical “Gears” Gruber & Galloway, 2008, Nature

  19. N-Cycle Feedbacks (inspired by Gruber 2004)

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