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Class 33

Class 33 . PRIMARY PRODUCTIVITY (PP) IN THE OCEANS Photosynthesis and Chemosynthesis Gross and Net Primary Production Cycling of organic matter Controlling factors Seasonal variations at different latitudes Global distribution . 1. Photosynthesis by phytoplankton is most important

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Class 33

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  1. Class 33 PRIMARY PRODUCTIVITY (PP) IN THE OCEANS Photosynthesis and Chemosynthesis Gross and Net Primary Production Cycling of organic matter Controlling factors Seasonal variations at different latitudes Global distribution

  2. 1. Photosynthesis by phytoplankton is most important CO2 + H2O - - - - - - - -> “C6H12O6” + O2 Sunlight Chlorophyll PRIMARY PRODUCTIVITY (PP) IN THE OCEANS PP = Synthesis of organic matter by autotrophs

  3. 2. Chemosynthesis, e.g., by sulfur bacteria at hydrothermal vents H2S + 2O2 - - - - - - - -> SO4= + Chemical Energy+ water CO2 + H2O - - - - - - - -> “C6H12O6” + O2 Bacteria Chemical Energy PRIMARY PRODUCTIVITY (PP) IN THE OCEANS

  4. PRIMARY PRODUCTIVITY (PP) IN THE OCEANS 3. Biosynthesis: Builds essential molecules for life C6H12O6 + nutrients (N, P, S, etc.) - - - - > proteins, lipids, DNA, etc.

  5. How much N and P are needed per gram of biomass produced? "Redfield ratio” (average for PP) [CH2O]106 [NH3]16 [H3PO4] C106 H263 O110 N16 P1

  6. Energy Biomass

  7. Energy and Biomass are transferred through a food web.

  8. Biomass

  9. Energy

  10. FATE OF ORGANIC MATTER -- HOW PP IS UTILIZED & CYCLED? • Gross Primary Productivity . . (GPP) • = Total amount of organic matter produced by primary producers (phytoplankton) • Net Primary Productivity . . (NPP) • = GPP minus energy utilized (organic matter respired) by phytoplankton for life processes • GPP and NPP are carbon uptake rates, g C / m2 - yr • Biomass, or "standing crop" is "density," g C / m2

  11. Organic matter used by phytoplankton to provide energy for themselves GPP- Total Production by Phytoplankton 70-90% 10-30% NPP-Phytoplankton Biomass available to fuel the rest of the food web

  12. ORGANIC MATTER RECYCLING • Almost complete recycling • Tiny amount lost via deposition in sediments (~0.1% of GPP)

  13. FACTORS CONTROLLING PRIMARY PRODUCTIVITY

  14. Seasonal Changes- Huge at High Latitude

  15. FACTORS CONTROLLING PRIMARY PRODUCTIVITY • 1. Sunlight- …in two different ways • Photosynthesis • Stratification of surface waters; caused by seasonal heating • Warm top layer- less dense • Sits on top (w/ phytoplankton)

  16. COLD • Winter mixing- convection • Phytoplankton get less light • But nutrients are brought up (for later)

  17. COLD 2. Nutrients: • Constantly removed from surface waters by PP and sinking of organic matter • Can be replenished by: • Winter mixing ...

  18. 2. Nutrients: • Constantly removed from surface waters by PP and sinking of organic matter • Can be replenished by: • Winter mixing ... • 2. Upwelling • 3. Land-derived nutrients (rivers, dust)

  19. Stratification- good and bad

  20. FACTORS CONTROLLING PRIMARY PRODUCTIVITY • 3. Grazing by herbivores: Reduces... • Amt of living Phytoplankton, and thus… • Rate of primary production

  21. Krill

  22. SEASONAL PRODUCTIVITY PATTERNS AT DIFFERENT LATITUDES

  23. SEASONAL PRODUCTIVITY PATTERNS AT DIFFERENT LATITUDES • 1. High-latitude: One intense spring/summer "bloom" • Nutrients abundant after winter mixing • Bloom initiated by increased sunlight • Warming --> water stratification • --> phytoplankton remain near surface- sun! • Productivity controlled mostly by sunlight

  24. Tropical oceans (low latitude) Relatively low productivity throughout the year • High-intensity sunlight all year • Density-stratified surface waters • Little vertical mixing, thus low nutrient levels • Exception: Upwelling areas. • Productivity controlled by nutrient availability

  25. Mid-latitude primary productivity: Complex annual cycle

  26. Mid-latitude: Spring + Late Summer "blooms” • Winter: • Mixing: Nutrients available • But sunlight is limiting

  27. Mid-latitude: Spring + Late Summer "blooms” • Spring: • Increased sunlight + water stratification • Intense bloom

  28. Mid-latitude: Spring + Late Summer "blooms” • Mid Summer: • Nutrients depleted • Grazing reduces phytoplankton biomass • Productivity decreases

  29. Mid-latitude: Spring + Late Summer "blooms” • Late Summer/ Early Fall: • Nutrients released (by death/decay; or excreted by animals) • --> Second, less intense bloom results

  30. Mid-latitude: Spring + Late Summer "blooms” Fig. 13-13

  31. Mid-latitude: Productivity controlled by both sunlight and nutrient availability

  32. Global Distribution of Primary Productivity

  33. 1. Open oceans- non-upwelling areas Low nutrients --> low PP rates 2. Open Ocean Upwelling areas: equatorial + High-Lat. --> Moderate to high PP rates

  34. 3. Continental shelves High nutrients (runoff; nutrients recycled- can’t sink out of surface system) --> high PP rates

  35. GLOBAL DISTRIBUTION OF PRIMARY PRODUCTIVITY (PP) (cont’d) 4. Coastal upwelling at low latitudes High nutrient supply + low-latitude sunlight --> very high PP rates 5. Estuaries Nutrients abundant- land runoff Very efficient nutrient recycling --> very high PP rates

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