class 33 primary productivity (pp) in the oceans photosynthesis and chemosynthesis gross and net...

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)