Georgia Tech Biological Oceanography Nutrient Cycles Nutrient limitation

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

Georgia Tech Biological Oceanography Marine N Limitation (Ryther & Dunstan 1971) EAS 4300 Guest Lecture Krebs, Fig. 25. 08 JPM

Georgia Tech Biological Oceanography 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 EAS 4300 Guest Lecture JPM

Georgia Tech Biological Oceanography Cyanobacterial bloom in the Baltic (www. eea. europa. eu) Eutrophication N inputs to coastal waters often promote algal blooms Dinoflagellate bloom off La Jolla (Photo: P. Franks, SIO) EAS 4300 Guest Lecture Agricultural runoff and blooms (Beman et al. 2005) JPM

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

Georgia Tech Biological Oceanography 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 EAS 4300 Guest Lecture Krebs, Fig. 25. 07 JPM

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

Georgia Tech Biological Oceanography Global N Cycle Cartoon Fluxes in Tg N y-1 land: < 200 ocean: > 400? Lightning: 3 Terr Nfix: 140 Pool sizes (Tg N) Atmosphere: Terr. Biota: Soil organics: Marine NO 3 -: Marine biota: 3. 9 x 109 13, 000 300, 000 570, 000 500 > 80 20 Marine NFix: >135 EAS 4300 Guest Lecture Crouzet et al. 1999, EEA JPM

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

Georgia Tech Biological Oceanography 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! EAS 4300 Guest Lecture JPM

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

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

Georgia Tech Biological Oceanography N* Distributions Reflect the Impact of N 2 -Fixation & Denitrification N* = 0. 87( [NO 3 -] - 16[PO 43 -] + 2. 9) EAS 4300 Guest Lecture (Gruber & Sarmiento 1999) Data: e. WOCE. Plot prepared with ODV JPM