Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE

1. Measurements and Models of Primary Productivity John J. Cullen Department of Oceanography, Dalhousie University Halifax, Nova Scotia, Canada B3H 4J1 Microbial Oceanography: Genomes to Biomes University of Hawai‘i June 28, 2007 Provided by the SeaWiFS Project, NASA/Goddard Space Flight Center and ORBIMAGE

2. Outline • What is marine primary productivity? • Ecological and biogeochemical significance • Scales of variability • Overview of measurements • The need for models • The nature of models • Their reliance on measurements • Hazards of forgetting the limitations of models

3. What is marine primary productivity? Net Primary Productivity (Production) Net rate of synthesis of organic material from inorganic compounds such as CO2 and water Chemosynthesis: chemical reducing power comes from reduced inorganic compounds such as H2S and NH3 Photosynthesis: reducing power comes from light energy Photosynthetic primary production is usually measured and considered to dominate. g C m-3 h-1 g C m-2 d-1

4. Oxygenic Photosynthesis This process can be quantified by measuring the increase of oxygen, the decrease of CO2, or the increase of organic carbon. For practical reasons, oceanographers measure the incorporation of radioactive 14C into organic compounds; some label water with 18O (stable isotope) and measure its appearance in oxygen. (Inferences can be made from 17O)

5. Ecological and biogeochemical significance marine.rutgers.edu/opp/ This is estimated primary productivity

6. The ocean accounts for half the photosynthesis on earth! marine.rutgers.edu/opp/ This is estimated primary productivity

7. Ecosystem Net Primary Productivity (1015 grams/year) Total Plant Biomass (1015 grams) Turnover Time (years) Marine 35-50 1-2 0.02-0.06 Terrestrial 50-70 600-1000 9-20 …and the point is??? From Falkowski and Raven 1997 Table 1.1

8. The Growth of Phytoplankton DaughterCell Photosynthesis Doubled Biomass Single Cell Daughter Cell Nutrient Uptake Cell Division Result: • More suspended particulate organic matter (food) • Less dissolved inorganic nutrients (N, P, Si) • Less dissolved inorganic carbon (CO2) –(Oxygen is produced)

9. What happens to the new growth? Fates: Accumulate (Bloom) Be eaten Sink Lysis (blow up) Viruses Apoptosis DaughterCell Daughter Cell Cell death site: www.uwm.edu/~berges/celldie/cldeth.htm

10. Consumption and Decomposition(deep ocean) Microbial Decomposition Organic Matter DEEP-SEA LIFE + Nutrients CO2 Consumption Respiration Excretion Result: • Less suspended particulate organic matter • More dissolved inorganic nutrients (N, P, Si) • Supersaturated dissolved inorganic carbon (CO2) • Oxygen is consumed

11. CO2 is elevated in the deep ocean because nutrients are depleted at the surface and regenerated at depth from a slide by Dave Karl

12. Ocean Cycle of Life and Death – At the Balance Point – CO2 CO2 + Nutrients  Organic Matter Primary production upwelling and mixing sinking particles CO2+ Nutrients  Organic Matter Decomposition Bottom Organic C Cullen et al. 2007 – Oceanography Mag.

13. Variability and disequilibrium structure food webs and biogeochemical cycles

14. Scales of variability:The co-occurrence of light and nutrients explainspatterns of primary productivity in the sea

15. Typical Structure of Chl and PP Sikes - MS 320 - Rutgers

16. Starting Point: The 14C method for measuring primary productivity HOT website

17. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 10 20 Depth (m) 30 40 ± s.e. 50 The 14C method for measuring primary productivity

18. An incredibly useful tool for time series and process studies HOT website

19. Interaction of physiology and vertical mixing is a big twist Denman, K. L., and A. E. Gargett (1983), Time and space scales of vertical mixing and advection of phytoplankton in the upper ocean, Limnol. Oceanogr., 28, 801-815. Lewis, M. R., et al. (1984), Relationships between vertical mixing and photoadaptation of phytoplankton: similarity criteria, Mar. Ecol. Prog. Ser., 15, 141-149. Cullen, J. J., and M. R. Lewis (1988), The kinetics of algal photoadaptation in the context of vertical mixing, J. Plankton Res., 10, 1039-1063. Franks, P. J. S., and J. Marra (1994), A simple new formulation for phytoplankton photoresponse and an application in a wind-driven mixed-layer model, Marine Ecology Progress Series, 111, 145-153.

20. Vertical mixing and temporal scales of measurements

21. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 10 20 Depth (m) 30 40 ± s.e. 50 Ideally, the 14C method measures net primary productivity Sometimes, it does 12 - 24 h incubations

22. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 Overestimation due to exclusion of UV-B 10 20 Depth (m) 30 40 ± s.e. 50 The measurement is subject toartifacts and biases 12 - 24 h incubations

23. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 Underestimation due to static incubation at excessive irradiance 10 20 Depth (m) 30 40 ± s.e. 50 The measurement is subject toartifacts and biases 12 - 24 h incubations

24. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 Underestimation due to dilution of intracellular DIC with respired cellular C 10 20 Depth (m) 30 40 ± s.e. 50 The measurement is subject toartifacts and biases 12 - 24 h incubations

25. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 10 Overestimation due to unnatural accumulation of biomass (disruption or exclusion of grazers) 20 Depth (m) 30 40 ± s.e. 50 The measurement is subject toartifacts and biases 12 - 24 h incubations

26. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 10 Underestimation due to food-web cycling (microbial respiration and excretion) 20 Depth (m) 30 40 ± s.e. 50 The measurement is subject toartifacts and biases 12 - 24 h incubations

27. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 10 20 Depth (m) 30 Overestimation due to inadequate time for respiration to be measured 40 50 The measurement is subject toartifacts and biases 12 - 24 h incubations

28. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 10 20 Depth (m) 30 40 50 …and that’s not all: Toxicity Relief of iron limitation Exposure to bright light Disruption of fragile cells for Simulated in situ: Poor match of irradiance Inappropriate temperature Possible diel bias 12 - 24 h incubations

29. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 10 20 Depth (m) 30 40 50 Productivity normalized to Chl is biased by: Changes in Chl during incubations Inadequate extraction of Chl by 90% acetone Interference from Chl b(fluorometric acid-ratio method) 12 - 24 h incubations

30. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 10 20 Depth (m) 30 40 50 and in general… Irradiance is not controlled Respiration is not accurately measured 12 - 24 h incubations

31. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 10 20 Depth (m) 30 40 ± s.e. 50 The measurement has its limitations Net production? Gross production? Overestimate? Underestimate?

32. Productivity (mgC m-3 d-1) 0 1 2 3 4 5 0 10 20 Depth (m) 30 40 ± s.e. 50 (extent depends on temperature, light and maybe nutrients) But we use it routinely Water column integral is something like net primary production (photosynthesis less losses to respiration)

33. Time Series Karl et al. In the new Steemann Nielsen volume …and it has served us very well

34. Process studies

35. marine.rutgers.edu/opp/ Direct Measurements will Never Provide Synoptic Estimates of Productivity

36. Models are required for many applications Productivity from ocean color Ecological prediction Biogeochemical models Climate change scenarios

37. PB / PBmax 0 0. 5 1 0 1 KPAR.z 2 3 4 Different EPAR/Ek 5 6 Many share the same basic form see Talling, Ryther and Yentsch, Rhode, etc.

38. Differences are relatively minor, butthey can matter Dependence on Irradiance Behrenfeld and Falkowski 1997a L&O

39. One approach: model the measurements Optical Depth Behrenfeld and Falkowski 1997a L&O

40. Simplified functions describe major patterns Behrenfeld and Falkowski 1997a L&O

41. 0 10 20 30 40 0 20 40 60 80 100 Is the measured/modeled pattern real? PB (mg C mg Chl-1 d-1) Measured near-surface inhibition Depth (m)

42. 0 10 20 30 40 0 20 40 60 80 100 Is the measured/modeled pattern real? PB (mg C mg Chl-1 d-1) or an artifact of fixed-depth incubation? Depth (m)

43. Measurements must be made on a shorter time scale Photosynthetron: Controlled laboratory incubation (Lewis and Smith 1983)

44. A comprehensive approach Cullen, J. J., M. R. Lewis, C. O. Davis, and R. T. Barber. 1992. Photosynthetic characteristics and estimated growth rates indicate grazing is the proximate control of primary production in the equatorial Pacific. Journal of Geophysical Research 97: 639-654. Approach introduced by Jitts, H. R., A. Morel, and Y. Saijo. 1976. The relation of oceanic primary production to available photosynthetic irradiance. Aust. J. Mar. Freshwater Res. 27: 441-454.

45. 0 0.08 0.2 0 0.4 0.8 0 0 10 10 20 20 30 30 40 40 50 50 Short-term measurements can detect near surface inhibition Chlorophyll a (mg m-3) PBm. Chl (mg C m-3 h-1) Depth (m) Depth (m) 0630 h: Chlorophyll and Pmax are nearly uniform in the 50-m mixed layer MORNING Principles described by Marra, Harris, Yentsch -- all prior to 1980

46. 0 0.08 0.2 0 0.4 0.8 0 0 10 10 20 20 30 30 40 40 50 50 Is measured near-surface inhibition real?Assessment with short-term P vs E Chlorophyll a (mg m-3) PBm. Chl (mg C m-3 h-1) Depth (m) Depth (m) 1215 h: Chlorophyll and Potential Productivity are still nearly uniform in the 50-m mixed layer MIDDAY

47. 0 0.08 0.2 0 0.4 0.8 0 0 10 10 20 20 30 30 40 40 50 50 Surface incubation led to artifact Chlorophyll a (mg m-3) PBm. Chl (mg C m-3 h-1) Depth (m) Depth (m) 1530 h: Fixed-depth incubations at the surface are “fried” — an artifact of sustained exposure 35% underestimation of ML productivity INCUBATED

48. 0 10 20 30 40 0 20 40 Error at the surface: big Error for integral: 8% 60 80 100 Conventional 14C:Near-surface inhibition is overestimated PB (mg C mg Chl-1 d-1) Artifact Depth (m)

49. Parameterization of an Artifact? Consequences for a model: minor except for irradiance dependence of P at higher daily irradiance Behrenfeld and Falkowski Consumer’s Guide: L&O 1997

50. Productivity (gC gChl-1 h-1) 0 1 2 3 4 5 0 10 UV-B Transparent Depth (m) 20 30 40 50 But remember…Near-surface inhibition is also underestimated Polycarbonate bottles exclude UV-B That’s a different talk… (this refers to 14C incubations of 12 - 24 hours)