Patterns of Productivity OCN 201 Biology Lecture 5 Production vs Biomass Biomass = amount of carbon per unit area (= standing stock * C/cell) Units (e.g.): g C m -2 Primary Production = amount of carbon fixed per unit area per unit time Units(e.g.): g C m -2 yr -1 both also commonly reported per unit volume (m -3 )
Primary Production - the production of autotrophic biomass Secondary Production - the production of heterotrophic biomass The production of heterotrophs depends upon the production of autotrophs What controls the production (growth) of autotrophs? Resource Limits on Primary Productivity Light 6CO 2 Cell + 6H 2 O C 6 H 12 O 6 + 6O 2 Nitrate Phosphate Nutrients Trace Metals
Respiration and Remineralization Energy Food C, N, P CO 2 + H 2 O Respiration & Remineralization NO 3 PO 4 Trace Metals Heterotrophic Organism Growth O 2 Limits on Primary Production Light Energy: amount depends on Depth Angle of the sun Nutrient Supply: depends on Import Recycling
Light Decreases with Depth Depth Effects on PP Photosynthesis or Respiration low high 0 Declines with Depth Depth (m) 50 Relatively Constant with Depth 100
Depth (m) Photosynthesis or Respiration low high 0 Gross Productivity 50 Net Productivity Compensation Depth Base of euphotic zone 100 Now add mixing... Photosynthesis or Respiration low high 0 phytoplankton are mixing Depth (m) 50 100 photosynthesizing respiring mixing controls availability of light
Sverdrup s critical depth theory (1953) intended to explain the timing of the spring bloom in the North Atlantic Mesoscale features also affect mixing, and nutrient and light availability (e.g., Mahadevan et al. 2012. Science) Key Concepts Primary productivity by phytoplankton is restricted to the surface ocean (that s where the light is) The euphotic zone refers to the zone above the compensation depth. Anywhere above that depth, photosynthesis exceeds respiration Typically - this occurs at ~1% light levels
Key Concepts Gross primary production: total organic material produced by autotrophs Net primary production: production remaining after subtracting respiratory needs of the autotrophs Compensation depth: depth at which gross primary production rate = respiration rate (Net productivity = 0) Light Intensity Varies with Angle of the Sun Solar angle varies daily, seasonally and with latitude Lower angles = lower energy density = more energy dissipated by atmosphere = less productivity
Sun Angle and Energy Noon Atmosphere Morning or Afternoon Earth Sun Angle and Energy Summer Winter
Sun Angle and Energy Tropical Polar
Ocean Color Limits on Primary Productivity Light Energy Cell 6CO 2 + 6H 2 O C 6 H 12 O 6 + 6O 2 Nutrients
Nutrient Limitation With sufficient light, growth will continue until nutrients run out Limiting nutrient: the nutrient that runs out first Exponential Growth Time
Amount Cells Time Amount Cells Phosphate Limiting Nutrient Nitrate Time
(Organic N & P) NO 3 PO 4 (Inorganic) NO 3 PO 4 Fecal Pellets Dead Animals Marine Snow Decompose Euphotic Zone Deeper Ocean Depth (m) Nutrient Concentration 0 5 10 15 20 25 30 0 500 1000 1500 2000 2500 3000 3500 4000 Nutrients depleted in euphotic zone Nutrients enriched in deep water
Most biomass in the sea is in the upper 200 meters Nutrients become depleted in most surface waters because of primary production Concentration Biomass Depth (m) Dissolved Nutrients NO 3 PO 4 (Inorganic) Mixing and Upwelling Recycle (decompose) Fecal Pellets Dead Animals Marine Snow Euphotic Zone Deeper Ocean NO 3 PO 4 Decompose
Modes of Production Regenerated Production: productivity based on nutrients that are recycled within the euphotic zone New Production: productivity based on nutrients imported (mixed or upwelled) into the euphotic zone Source of New Production Mixing by storms, high winds - Strong density stratification inhibits mixing - Stratification greatest in the tropics Upwelling (coastal or equatorial)
Equatorial Upwelling Equatorial Upwelling
Coastal Upwelling Coastal Upwelling
Nutrients are stripped from surface waters by photosynthesis and lost to deep water Areas with upwelling or deep mixing by storms are very productive because nutrients are returned to the surface Key Concepts Areas with little mixing or upwelling become nutrient limited and have low productivity EVEN IF THERE IS LOTS OF LIGHT Patterns of Productivity
Seasonal Productivity Tropical (Upwelling) Poles Seasonal productivity Polar productivity latitude Temperate productivity light nutrients light Tropics Tropical productivity Winter Spring Summer Autumn Winter (schematic after Lalli & Parsons Fig 3.9)
Productivity Patterns Tropics (except equator): Lots of sunlight, but low nutrients due to strong thermal stratification = persistently low productivity Equatorial upwelling: strong upwelling and lots of sunlight = persistently high productivity Temperate: Seasonal deep mixing of nutrients plus moderate sunlight = spring bloom, small fall bloom Polar: High nutrients, but light limited except during summer = one major summer bloom Questions?