1. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM Nutrient Cycles Nutrient limitation –N sources N Cycle –Budget –N 2 Fixation Links to the C Cycle

2. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM Krebs, Fig. 25.08 Marine N Limitation (Ryther & Dunstan 1971)

3. 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

4. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM Eutrophication N 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)

5. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM Surface Nutrient Distribution Data: eWOCE. Plot prepared with ODV

6. 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

7. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM N-Cycle as a Redox Web (Modified from Codispoti 2001and Liu 1979)

8. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM Marine NFix: >135 land: < 200 ocean: > 400? Terr Nfix: 140 Lightning: 3 20 > 80 Crouzet et al. 1999, EEA Pool sizes (Tg N) Atmosphere:3.9 x 10 9 Terr. Biota: 13,000 Soil organics:300,000 Marine NO 3 - :570,000 Marine biota:500 Global N Cycle Cartoon Fluxes in Tg N y -1

9. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM Oceanic Nitrogen Budget Estimates

10. 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). N 2 -fixation plays a key role in regulating the global C cycle but we still don’t how much N 2 -fixation is occurring in the ocean, who’s doing it, and where!

11. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM NH 4 + New vs. Regenerated Production modified from http://www.up.ethz.ch/research/nitrogen_cycle/index Biological Pump

12. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM North Atlantic Nutrient Ratios Data: eWOCE. Plot prepared with ODV

13. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM N* Distributions Reflect the Impact of N 2 -Fixation & Denitrification Data: eWOCE. Plot prepared with ODV N* = 0.87( [NO 3 - ] - 16[PO 4 3- ] + 2.9) (Gruber & Sarmiento 1999)

14. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM Diazotroph Diversity (Images courtesy R. Foster ) (Zehr et al., 2001. Nature 412 ) ?

15. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM KM0703: 11 Mar – 15 Apr 2007

16. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM KM0703 Stns. 4 - 10 Group A Abundance (Moisander et al., in prep)

17. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM KM0703 Areal N 2 -Fixation Rates Areal Rate ( µmole m -2 d -1 )

18. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM Gruber & Galloway, 2008, Nature Biogeochemical “Gears” Fluxes in Tg N y -1

19. EAS 4300 Guest Lecture Georgia Tech Biological Oceanography JPM (inspired by Gruber 2004) N-Cycle Feedbacks