“The open ocean is a biological desert.”

1. “The open ocean is a biological desert.”

2. Primary Production Global chlorophyll concentrations for Oct. 2000

3. Feb 5, 1998: uniformly low pigment concentrations during all seasons

4. Primary productivity • Primary productivity is the amount of carbon (organic matter) produced by organisms • Mostly through photosynthesis • Energy source = solar radiation • Also includes chemosynthesis • Energy source = chemical reactions

5. Photosynthetic productivity

6. Primary Producers Common Name Blue-green algae (cyanobacteria) Red algae Brown algae Green algae Coccolithophorids Dinoflagellates Diatoms Seagrass

7. Oceanic photosynthetic productivity • Controlling factors affecting photosynthetic productivity: • Availability of nutrients • Nitrates • Phosphates • Iron • Amount of sunlight • Varies daily and seasonally • Sunlight strong enough to support photosynthesis occurs only to a depth of 100 meters (euphotic zone)

8. Locations of maximum photosynthetic productivity • Coastlines • Abundant supply of nutrients from land • Water shallow enough for light to penetrate all the way to the sea floor • Upwelling areas • Cool, nutrient-rich deep water is brought to the sunlit surface

9. Upwelling

10. Coastal upwelling

11. The electromagnetic spectrum and light penetration in seawater

12. Water color and life in the ocean • Ocean color is influenced by: • The amount of turbidity from runoff • The amount of photosynthetic pigment, which corresponds to the amount of productivity • Yellow-green = highly productive water • Found in coastal and upwelling areas (eutrophic) • Clear indigo blue = low productivity water • Found in the tropics and open ocean (oligotrophic)

13. Table 1. Average net primary production and biomass of aquatic habitats. Data from R.H. Whittaker and G.E. Likens, Human Ecol. 1: 357-369 (1973).

14. Productivity varies TEMPORALLY and SPATIALLY: • generally highest over continental shelves; over the shelf itself it is highest just offshore • seasonality more pronounced at high latitudes • at mid latitudes, productivity peaks both spring and fall Observations from September 1997 through July 2005

15. Thermocline depth Temperature profile

16. Regional productivity • Photosynthetic productivity varies due to: • Amount of sunlight • Availability of nutrients • Thermocline (a layer of rapidly changing temperature) limits nutrient supply • Examine three open ocean regions: • Polar oceans (>60° latitude) • Tropical oceans (<30° latitude) • Temperate oceans (30-60° latitude)

17. Productivity in tropical, temperate, and polar oceans Zooplankton

18. Productivity polar oceans

19. Productivity in tropical oceans

20. Productivity in temperate oceans

21. Plankton Sampling

24. Plankton Size • Picoplankton (.2-2 µm) • Nanoplankton (2 - 20 µm) • Microplankton (20-200 µm) • Macroplankton (200-2,000 µm) • Megaplankton (> 2,000 µm) microplankton picoplankton nanplankton

25. R=P

26. Primary Productivity • Gross Primary Productivity (GPP) • The rate of production of organic matter from inorganic materials by autotrophic organisms • Respiration (R) • The rate of consumption of organic matter (conversion to inorganic matter) by organisms. • Net Primary Productivity (NPP) • The net rate of organic matter produced as a consequence of both GPP and R.

27. Primary Productivity NPP = GPP - R

28. Photosynthesis: light + 6CO2 + 6H2O C6H12O6 + 6O2 Light & Dark Experiments zooplankton phytoplankton Respiration: C6H12O6 + 6O2 6CO2 + 6H2O decomposition

29. dark bottle light bottle respiration photosynthesis + respiration weight

30. Calculating Primary Productivity Assume that our incubation period was 1 hour. Measured oxygen concentrations: Initial bottle = 8 mg O2 /L Light bottle = 10 mg O2 /L Dark bottle = 5 mg O2 /L (Light - Initial) = (10 - 8) = 2 mg/L/hr = (GPP - R) = NPP (Initial - Dark) = (8 - 5) = 3 mg/L/hr = Respiration (Light - Dark) = (10 - 5) = 5 mg/L/hr = (NPP + R) = GPP

31. Environmental Factors Affecting Primary Production (eutrophication)

32. Inquiry • Why is the open ocean a biological desert? • Where are the most productive regions located? • Describe productivity in temperate, polar and tropical water. • Why does the zooplankton lag behind the phytoplankton? • If you want to catch microplankton, what size mesh net do you need? • Why can’t plants grow below the compensation depth? • Why does eutrophication sometimes result in mass fish kills?