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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
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PRIMARY PRODUCTIVITY (PP) IN THE OCEANS PP = Synthesis of organic matter by autotrophs 1. Photosynthesis by phytoplankton is most important CO 2 + H 2 O - - - - - - - -> “C 6 H 12 O 6 ” + O 2 Sunlight Chlorophyll
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PRIMARY PRODUCTIVITY (PP) IN THE OCEANS 2. Chemosynthesis, e.g., by sulfur bacteria at hydrothermal vents H 2 S + 2O 2 - - - - - - - -> SO 4 = + Chemical Energy+ water CO 2 + H 2 O - - - - - - - -> “C 6 H 12 O 6 ” + O 2 Bacteria Chemical Energy
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PRIMARY PRODUCTIVITY (PP) IN THE OCEANS 3. Biosynthesis: Builds essential molecules for life C 6 H 12 O 6 + nutrients (N, P, S, etc.) - - - - > proteins, lipids, DNA, etc.
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How much N and P are needed per gram of biomass produced? "Redfield ratio” (average for PP) [CH 2 O] 106 [NH 3 ] 16 [H 3 PO 4 ] C 106 H 263 O 110 N 16 P 1
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EnergyBiomass
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Energy and Biomass are transferred through a food web.
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Biomass
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Energy
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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 / m 2 - yr Biomass, or "standing crop" is "density," g C / m 2 FATE OF ORGANIC MATTER -- HOW PP IS UTILIZED & CYCLED?
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GPP- Total Production by Phytoplankton Organic matter used by phytoplankton to provide energy for themselves 70-90% NPP-Phytoplankton Biomass available to fuel the rest of the food web 10-30%
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Almost complete recycling Tiny amount lost via deposition in sediments (~0.1% of GPP) ORGANIC MATTER RECYCLING
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FACTORS CONTROLLING PRIMARY PRODUCTIVITY
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Seasonal Changes- Huge at High Latitude
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1. Sunlight- …in two different ways A.Photosynthesis B.Stratification of surface waters; caused by seasonal heating –Warm top layer- less dense –Sits on top (w/ phytoplankton) FACTORS CONTROLLING PRIMARY PRODUCTIVITY
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Winter mixing- convection Phytoplankton get less lightPhytoplankton get less light But nutrients are brought up (for later)But nutrients are brought up (for later) COLD
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Constantly removed from surface waters by PP and sinking of organic matter Can be replenished by: 1.Winter mixing... 2. Nutrients: COLD
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Constantly removed from surface waters by PP and sinking of organic matter Can be replenished by: 1.Winter mixing... 2. Upwelling 3. Land-derived nutrients (rivers, dust) 2. Nutrients:
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Stratification- good and bad
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3. Grazing by herbivores: Reduces... Amt of living Phytoplankton, and thus…Amt of living Phytoplankton, and thus… Rate of primary productionRate of primary production FACTORS CONTROLLING PRIMARY PRODUCTIVITY
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Krill
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SEASONAL PRODUCTIVITY PATTERNS AT DIFFERENT LATITUDES
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1. High-latitude: One intense spring/summer "bloom" Nutrients abundant after winter mixingNutrients abundant after winter mixing Bloom initiated by increased sunlightBloom initiated by increased sunlight Warming --> water stratificationWarming --> water stratification --> phytoplankton remain near surface- sun! Productivity controlled mostly by sunlight SEASONAL PRODUCTIVITY PATTERNS AT DIFFERENT LATITUDES
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High-intensity sunlight all year Density-stratified surface watersDensity-stratified surface waters Little vertical mixing, thus low nutrient levelsLittle vertical mixing, thus low nutrient levels Exception: Upwelling areas.Exception: Upwelling areas. Productivity controlled by nutrient availability Tropical oceans (low latitude) Relatively low productivity throughout the year
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Mid-latitude primary productivity: Complex annual cycle
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Winter: Mixing: Nutrients available But sunlight is limiting Mid-latitude: Spring + Late Summer "blooms”
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Spring: Increased sunlight + water stratification Intense bloom Mid-latitude: Spring + Late Summer "blooms”
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Mid Summer: Nutrients depleted Grazing reduces phytoplankton biomass Productivity decreases Mid-latitude: Spring + Late Summer "blooms”
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Late Summer/ Early Fall: Nutrients released (by death/decay; or excreted by animals) --> Second, less intense bloom results Mid-latitude: Spring + Late Summer "blooms”
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Fig. 13-13 Mid-latitude: Spring + Late Summer "blooms”
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Mid-latitude: Productivity controlled by both sunlight and nutrient availability
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Global Distribution of Primary Productivity
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1. Open oceans- non-upwelling areas Low nutrients --> low PP rates 2. Open Ocean Upwelling areas: equatorial + High-Lat. --> Moderate to high PP rates
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3. Continental shelves High nutrients (runoff; nutrients recycled- can’t sink out of surface system) --> high PP rates
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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 GLOBAL DISTRIBUTION OF PRIMARY PRODUCTIVITY (PP) (cont’d)
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