Ocean Productivity: Concepts and Measurements

1. Ocean Productivity:Concepts and Measurements John Marra Brooklyn College, CUNY ACE workshop

2. The Major Goal of Biological Oceanography: “…determination of time-varying plankton productivity in the world ocean…” -Barber and Hilting (2002) ACE workshop

3. Concepts • Productivity • Autotrophs, heterotrophs • New production • Export Production ACE workshop

4. Productivity Defined Ecological Term Process Rate of photosynthesis Gross primary production, GPP - Ra GPP - autotrophic respiration Net primary production, NPP - - Rhet Ra NPP - heterotrophic respiration Net community production, NCP Export Production, EP, the amount of NCP exported (sinking, mixing, ZP vertical migration) to depth New Production, NP, the fraction of NPP supported by ‘new’ nutrients, and available for export ACE workshop

5. Photosynthesis Carbon dioxide + Water Sugars + Oxygen The Photosynthetic Quotient, or PQ is the amount of oxygen evolved relative to the carbon fixed into organic matter ACE workshop

6. Synthesis of Energy from Light ACE workshop

7. Productivity Measurements • Two choices: • Fluxes from in situ dynamics • Fluxes occurring in bottles • Each has advantages and disadvantages ACE workshop

8. The kind of ‘container’ Very physically dynamic in situ volume Very non-dynamic volume ACE workshop

9. Oxygen CO2 + H2O -> CH2O + O2 The change in oxygen content in a defined quantity of water is the most straightforward measure of Net Community Production. The problems: All too frequently, the change is negative (NCP <0) over 12 or 24 h; 2. Requires an accurate air-sea exchange ACE workshop

10. 18Oxygen CO2 + H218O -> CH2O + 18O2 A good estimate of Gross Primary Production, but may be influenced by the Mehler reaction, or other oxygen consuming reactions within the phytoplankton cell. ACE workshop

11. Carbon CO2+ H2O -> CH2O + O2 • It’s carbon! (no worries about value of the the photosynthetic quotient), but… • Precision is too low for most open ocean work ACE workshop

12. 14Carbon 14CO2 + H2O -> 14CH2O + O2 • Basis of virtually all satellite algorithms for productivity • Incubation from dawn-dusk very close to Net Primary Production • Characteristics invite methodological abuse and carelessness • Easy • Extremely Sensitive • Always gives a ‘positive’ answer ACE workshop

13. “…the results of the 14C method fall somewhere between the net phytoplankton production and total photosynthesis, but exact evaluation of the meaning of the experiments will require an extensive experimental programme” G. A. Riley (ca. 1954) ACE workshop

14. Productivity has known limits 1. Growth rate as a function of temperature (Eppley,1972) 2. The maximum rate of photo-synthesis normalized to chlorophyll-a, Pbmax, will be ≤ 25 3. The quantum yield. 8 quanta of light are required to evolve 1 mol O2, thus, the quantum yield will be < 0.1 (in practice) (Falkowski, 1981) (e.g., Bannister and Weidemann, 1983) ACE workshop

15. Biomass: Changes in POC • Good for estimating particle production • Doesn’t measure DOC production • There are many more optically-based measurements of production in development ACE workshop

16. Comparing Fluxes: In Situ and in Containers ACE workshop

17. The JGOFS North Atlantic Bloom Experiment, Spring 1989 Over 13 days (mixed layer): • Production = 970 mmols C m-2 • Total increase in POC = 520 mmols C m-2 • Trap flux = 507 mmols C m-2 • (234Th estimates are about half the trap flux.) m ACE workshop

18. N interacts with C in the concept of New Production • The amount of production fueled by NO3 or N2 and called the f-ratio • Best for temperate, and high-latitude areas subject to seasonal mixing, and supply of NO3 from depth • A good way to evaluate the quantity of production exported to depth Total Production Re-generated N2 New NO3 ACE workshop

19. ACE workshop

20. Export Production in Time ‘bottom up’ regulation grazing ‘top down’ regulation ACE workshop

21. Export Flux to Depth ACE workshop

22. The role of Iron Boyd et al., 2007 ACE workshop

23. Next steps: What we don’t know • Production and dynamics of dissolved organic matter (DOM) • Respiration and its components • The depth of the Euphotic Zone • Production in large, permeable, diffusive containers in terms of small, impermeable ones, and vice versa ACE workshop

24. Dissolved Organic Matter COASTAL OCEAN OPEN OCEAN Riverineinputs CO2 Net Primary Production Net Primary Production solubilization, grazing, exudation, lysis, solubilization, grazing, exudation, lysis, EXCHANGE DOM DOM Surface CDOM CDOM DIC Mixing/Advection Mixing/advection DIC DOM long term C reservoir hydrolysis/ diagenesis Deep ACE workshop CDOM SEDIMENTS adapted from Moore 1999

25. CO2 CO2 Phytoplankton Primary Production Bacterial remineralization Bacterial remineralization inorganic compounds extracellular release, grazing, lysis, solubilization bioavailability DOM Lateral transport Export to deeper waters & sediments through aggregate and particulate sinking Advection • Estimated that 50% of primary production routed through dissolved fraction • Not typically measured in measurements of productivity • O2 evolution/CO2 consumption will include it, • 14C uptake may not • Won’t be measured in particle production methods • Ultimately comes from photosynthesis (like everything else) • Utilization of labile DOC will be as rapid as photosynthetic production ACE workshop

26. BACTERIAL AUTOTROPH RESPIRATION DISSOLVED ORGANIC MATTER EUPHOTIC DEPTH ACE workshop

27. Global Ocean Productivity Through the ‘Ages’ ACE workshop

28. ACE workshop

29. Cast of Characters ACE workshop

30. ACE workshop