Photosynthesis II

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Primary Production MARE 444 Dr. Jason Turner
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Primary Productivity
- Production is highly variable - gt 95 of
marine 1o production by phytoplankton -
Traditional view most by net plankton (diatoms
dinos) - Modern view nanoplankton
picoplankton extremely important ( 60-90 of
1o production in some systems)
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Primary Productivity
However...
Open Sea comprises gt 90 of the area of Worlds
Oceans
Therefore...
Overwhelming of marine production via
phytoplankton in oceanic waters
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Primary Productivity
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Are all Oceans Created Equally?
Coastal upwelling gt 500 g C/m2/yr
Eq. upwelling gt 200-300 g C/m2/yr
Open Ocean 100 g C/m2/yr
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Primary Productivity
How can you measure the rate of
accumulation? Net photosynthesis (P) photosyn
(R) resp Gross photosynthesis (P R)
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Critical Depth Model
Plants respire (R) independent of depth
(constant) Plants photosynthesize (P) less with
depth (light penetration decreases with depth)
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Compensation Depth
is water depth at which instantaneous
photosynthetic production is equal to
instantaneous plant respiration
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Critical Depth
is water depth at which R P as totaled over
the whole water column
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Critical Depth and Mixing Depth
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What if phytoplankton mix is below critical depth?
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Measuring Primary Productivity
- oxygen is released in proportion to amount
of photosynthesis (premise DO production
measured in oxygen-tight biological oxygen demand
(BOD) bottles)
- radioactive 14C tracer uptake of
bicarbonate during photosynthesis (premise
production equivalent to percentage of the
radioactive label C taken up by phytoplankton)
- photosynthesis estimated by measuring
fluorescence obtained from phytoplankton that
have been exposed light flashes (premise
photosynthetic pigments fluoresce when exposed to
UV light)
-Satellites with color scanners measure
visible light that leaves the water
(radiance) (premise phytoplankton absorb green
- more blue light reaches scanner when
phytoplankton are denser at the surface)
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Satellite-acquired ocean color data (NASA)
Premise radiance reflected from ocean in visible
range is related to concentration of chl other
pigments
SEA-VIEWING WIDE-FIELD-OF-VIEW SENSOR (SeaWiFS)
High chl
Blue light hits scanner
Light in green part of spectrum absorbed
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Fluorometry
1. Cone projects flashes of light at a specific
wavelength - Plankton in the water absorb the
light and respond by emitting a tiny amount of
light of a different wavelength. 2. This cone
measures the amount of light produced by the
plankton. 3. Contains electronics to process
the data and transmit them to the CTD for
delivery to the surface.
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Light-dark bottle experiment
Collect sample Put half in a light bottle, half
in a dark bottle Measure dissolved oxygen
concentrations in both Let bottles sit for a set
length of time Light bottle (P - R) oxygen will
? Dark bottle (R) oxygen will ?
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Light-dark bottle experiment
Light bottle Dark bottle
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Oxygen the network for plankton
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Light-dark bottle experiment
Light bottle Dark bottle (P - R) R P
Gross Primary Production
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So How Does it Work?
If Pair 2 P R? Then Compensation depth
at If Pair 5 P R? Then Compensation
depth at
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Productivity versus Standing Stock
Productivity is a rate Standing stock is amount
of biomass chlorophyll Discrete (samples analyzed
on a fluorometer) remote sensing cell
numbers cell volumes
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Chlorophyll-based environmental classification
(low nutrients) - chlorophyll concentrations
lt0.05 µg/L in surface waters, 0.1-0.5 µg/L at
depths of 100-150 m - have many k-selected
species, dependent on a different limiting
factors Community as a whole tends to be at
equilibrium with the total nutrient supply
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Chlorophyll-based environmental classification
(high nutrients) - chlorophyll concentrations
of 1-10 µg/L in surface waters (Hilo Bay 0.4 - 5
µg/L) waters tend to be dominated by one or
two fast-growing, r-selected species (moderate
nutrients) - chlorophyll concentrations tend to
be lt 1 µg/L, k- and r-selected species present
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Abiotic Factors
Light Turbidity more particles in the water,
less light penetration Latitude light
intensity decreases from equator towards
the poles Nutrients Mixing winds increase from
equator towards the poles Upwelling
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The Facts of Light
- the surface waters of the oceans that
receive sufficient light to support
photosynthesis - the part of the ocean where
sunlight is absent - the area of low light
lying between the euphotic and aphotic zones.
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Light
Light Highest in surface
waters Fate of light absorbed or scattered
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Let there be Light
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Light my Fire
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Light and Nutrients
Tend to have an inverse relationship More
nutrients/less light More light/less
nutrients
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Light versus nutrients
more
light
nutrients
less
nearshore (or pole)
offshore (or equator)
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Oceanic Nutrients
Major nutrients required for phytoplankton growth
and reproduction Nitrogen Nitrate (NO3-),
Nitrite (NO22-), Ammonium (NH4) Phosphorus
Phosphate (PO43-)
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Oceanic Nutrients
Occur in small amounts in seawater limit
production Most oceans nutrient-poor deserts
For Example...
Agricultural soil averages Nitrogen in upper 1
m Production of 50,000g dry organic matter / 1m3
Richest ocean water averages Production of 5g
dry organic matter / 1m3
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Oceanic Nutrients
However...
Plankton have access to much more nutrient
habitat than terrestrial plants
Why??? Terrestrial plants utilize 1-2 m or soil
depth Plankton production can exist as deep as
100-120 m
Plankton should produce 500g / 100m3 (1m2 x 100 m
deep) Usually only capable of 25g
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Effects of Nutrient Availability
Redfield Ratios elemental composition in terms
of atoms relative to phosphorus of organic matter
in typical phytoplankton P N C 1 15.5
108 Since phosphorus and nitrogen are of limited
supply in oceanic systems they limit plankton
production in the sea
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Michaelis-Menton Functions
Michaelis-Menton equation often used to
represent nutrient limitation for phytoplankton
Measure of velocity of reactions at various
substrate concentrations
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Iron Revolution
Why are there no plankton blooms in areas of the
oceans with high levels of N, P, Si?
Iron Limitation in some areas?
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Factors Limiting Ocean Nutrients
1. Nutrient content not constant 2. Production
reduced at depth 3. Organisms reduce water
volume 4. Nutrients absorbed by other autotrophs
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