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
PRIMARY PRODUCTIVITY (PP) IN THE OCEANS
PP = Synthesis of organic matter by autotrophs
1. Photosynthesis by phytoplankton is most important
CO2 + H2O - - - - - - - -> “C6H12O6” + O2
Sunlight
Chlorophyll
PRIMARY PRODUCTIVITY (PP) IN THE OCEANS
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
3. Biosynthesis: Builds essential molecules for life
C6H12O6 + nutrients (N, P, S, etc.) - - - - > proteins, lipids, DNA, etc.
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
Energy Biomass
Energy and Biomass are transferred through a food web.
Biomass
Energy
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
FATE OF ORGANIC MATTER -- HOW PP IS UTILIZED & CYCLED?
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%
• Almost complete recycling• Tiny amount lost via deposition in sediments
(~0.1% of GPP)
ORGANIC MATTER RECYCLING
FACTORS CONTROLLING FACTORS CONTROLLING PRIMARY PRODUCTIVITYPRIMARY PRODUCTIVITY
Seasonal Changes- Huge at High Latitude
1. Sunlight- …in two different ways1. Sunlight- …in two different ways
A.A. PhotosynthesisPhotosynthesis
B.B. Stratification of surface waters; caused by Stratification of surface waters; caused by seasonal heatingseasonal heating
– Warm top layer- less denseWarm top layer- less dense– Sits on top (w/ phytoplankton)Sits on top (w/ phytoplankton)
FACTORS CONTROLLING PRIMARY PRODUCTIVITYFACTORS CONTROLLING PRIMARY PRODUCTIVITY
Winter mixing- convectionWinter mixing- convection• Phytoplankton get less lightPhytoplankton get less light• But But nutrients are brought up (for later)nutrients are brought up (for later)
COLD
Constantly removed from surface waters by PP Constantly removed from surface waters by PP and sinking of organic matterand sinking of organic matter
Can be replenished by:Can be replenished by:
1.1. Winter mixing ... Winter mixing ...
2. Nutrients:2. Nutrients:
COLD
Constantly removed from surface waters by PP Constantly removed from surface waters by PP and sinking of organic matterand sinking of organic matter
Can be replenished by:Can be replenished by:
1.1. Winter mixing ... Winter mixing ...
2. Upwelling2. Upwelling
3. Land-derived nutrients (rivers, dust)3. Land-derived nutrients (rivers, dust)
2. Nutrients:2. Nutrients:
Stratification- good and bad
3. Grazing by herbivores: Reduces...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 FACTORS CONTROLLING PRIMARY PRODUCTIVITYPRIMARY PRODUCTIVITY
Krill
SEASONAL PRODUCTIVITY PATTERNSSEASONAL PRODUCTIVITY PATTERNSAT DIFFERENT LATITUDESAT DIFFERENT LATITUDES
1. High-latitude1. High-latitude: One intense spring/summer "bloom": 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 stratification Warming --> water stratification
--> phytoplankton remain near surface- sun!--> phytoplankton remain near surface- sun!
Productivity controlled mostly by sunlightProductivity controlled mostly by sunlight
SEASONAL PRODUCTIVITY PATTERNSSEASONAL PRODUCTIVITY PATTERNSAT DIFFERENT LATITUDESAT DIFFERENT LATITUDES
High-intensity sunlight all year 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 availabilityProductivity controlled by nutrient availability
Tropical oceansTropical oceans (low latitude) (low latitude)Relatively low productivity Relatively low productivity
throughout the yearthroughout the year
Mid-latitude primary productivity: Complex annual cycle
Winter:• Mixing: Nutrients available• But sunlight is limiting
Mid-latitude: Spring + Late Summer "blooms”
Spring:• Increased sunlight + water stratification• Intense bloom
Mid-latitude: Spring + Late Summer "blooms”
Mid Summer: • Nutrients depleted • Grazing reduces phytoplankton biomass• Productivity decreases
Mid-latitude: Spring + Late Summer "blooms”
Late Summer/ Early Fall:• Nutrients released (by death/decay; or excreted by animals)•--> Second, less intense bloom results
Mid-latitude: Spring + Late Summer "blooms”
Fig. 13-13
Mid-latitude: Spring + Late Summer "blooms”
Mid-latitude:
Productivity controlled by both sunlight and nutrient availability
Global Distribution of Primary Productivity
1. Open oceans- non-upwelling areas
Low nutrients --> low PP rates
2. Open Ocean Upwelling areas: equatorial + High-Lat. --> Moderate to high PP rates
3. Continental shelves
High nutrients (runoff; nutrients recycled- can’t sink out of surface system)
--> high PP rates
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)