1. Biology of mixed layer Primary production
Irradiance
Phytoplankton
Physical mixing
processes
Nutrients
Primary production
by Phytoplankton - small drifting organisms that photosynthesize
Competition and limits on production

2. Photosynthesis (P) Carbon dioxide (C,O) + Water (H,O)
Requires chloroplasts
Plants, algae
Carbon dioxide (C,O)
+ Water (H,O)
+ Nutrients (N,P)
+ Light energy
Oxygen (O)
+ Organic matter (C,H,O,N,P)
proteins
fats
carbohydrates
nucleic acids

3. Every living thing respires (plants too!)
Respiration (R)
Every living thing respires (plants too!)
Carbon dioxide (C,O)
+ Water (H,O)
+ Nutrients (N,P)
Oxygen (O)
+ Organic matter (C,H,O,N,P)
proteins
fats
carbohydrates
nucleic acids

4. Primary Production - Definitions
Gross Primary Production (GPP) =
rate of carbon fixation by photosynthesis
units = [Mass / Area / Time], e.g. [g C m-2 y-1]
Respiration (R) =
rate of carbon (CO2) loss through metabolism
Net Primary Production (NPP) = GPP - ΣR
Need GPP>ΣR for net growth!

5. Production ≠ Biomass Production is a rate e.g. [g C m-2 y-1]
Biomass is a
concentration
e.g. [g C m-2]

6. “Paradox of the Plankton” There are many species of phytoplankton, despite few limiting resources and lots of mixing.
Phytoplankton (single-celled primary producers) have various competitive strategies that enable coexistence.

7. Four major players Cyanobacteria Diatoms Coccolithophores
Dinoflagellates
Small (<1 μm) or
Large (0.5-4 mm)
Nitrogen fixers
Large (2-200 μm)
Have silica frustules
Small (2-25 μm)
Have CaCO3 tests
Large ( μm)
Have unique life
cycle & blooms

8. What limits production?
Nutrients
Light
Intensity
Spectrum
Temperature
Grazing by zooplankton
Write the general equation on the board here

9. The environment varies in space and time
The environment varies in space and time. Different phytoplankton grow well under different conditions.
High Low
Nutrients
Low High
Light Intensity
Deep water / Winter
Shallow water / Summer
Narrow Broad
Light Spectrum
Low High
Temperature

10. Nutrients N, P, Si, Fe Nitrogen is most often limiting in ocean
Bioavailable forms of inorganic N:
Nitrate (NO3-)
Ammonium (NH4+)
Nitrite (NO2-)

11. Growth rate varies with [nutrient]
μ = Specific growth rate (d-1)
Curve “saturates”
Specific growth rate is defined as the increase in cell mass per unit cell mass per unit time
N = [Nutrient]

12. Growth rate varies with [nutrient]
μ = Specific growth rate (d-1) Ks
μmax/2
μmax
Specific growth rate is defined as the increase in cell mass per unit cell mass per unit time
“half-saturation
constant”
N = [Nutrient]

13. Growth rate varies with [nutrient]
μ = Specific growth rate (d-1) Ks
μmax/2
μmax
Michaelis-Menten Kinetics
Specific growth rate is defined as the increase in cell mass per unit cell mass per unit time
“half-saturation
constant”
N = [Nutrient]

14. At low nutrient concentrations, smaller phytoplankton tend to grow faster
Assume cell is a sphere.
Surface area:
Volume:
Surface area to volume ratio:
Smaller cells have relatively more surface area
for taking up nutrients.

15. Different strategies of nutrient use
Coccolithophores
Low μmax
Low Ks
Diatoms
High μmax
High Ks
High or variable nutrients
High mixing, upwelling
Low average irradiance
High turbulence
Chronically low nutrients
Stratified conditions
High average irradiance
Low turbulence

16. Light Intensity / Irradiance
Larger plankton (diatoms and dinoflagellates) most adapted to high-nutrient conditions.
High Low
Nutrients
Low High
Light Intensity / Irradiance
Deep water / Winter
Shallow water / Summer
Narrow Broad
Light Spectrum
Low High
Temperature

17. PAR = photosynthetically active radiation (visible light wavelengths)
Irradiance = power of electromagnetic radiation per unit area of ocean’s surface (e.g. W m-2) - or -
energy per area per time (e.g. mol photons m-2 s-1).

18. Light (PAR) attenuates with depthIz Z0
Iz = irradiance at depth z
Units of [Watts m-2] or
[mol photons m-2 s-1]
Light attenuates as it is absorbed and scattered by particles in the water. Z

19. Average Primary Production saturates at high PAR (photosynthetically active radiation)
Inside Fe patch
Outside Fe patch
Hiscock et al. 2008

20. Species adapt to different light levels
Irradiance 1
Photo-inhibition
at high light levels
Ryther 1956
Too much light damages cells and reduces photosynthesis (photo-inhibition)

21. Diatoms most adapted to low-light conditions
High Low
Nutrients
Low High
Light Intensity / Irradiance
Deep water / Winter
Shallow water / Summer
Narrow Broad
Light Spectrum
Low High
Temperature

22. Attenuation varies with wavelength.
More wavelengths are available near the surface.
Plankton use colored pigments to harvest light at different wavelengths.
violet red

23. Different color pigments absorb different wavelengths of light
Pigments (colored molecules)
Phytoplankton with different pigments
Chlorophyll*

24. Phytoplankton with multiple pigments capture more wavelengths
All phytoplankton have chlorophyll
Coccolithophores and diatoms have carotenoids
Cyanobacteria have phycoerythrin, phycocyanin

25. Light Intensity / Irradiance
Coccolithophores and Cyanobacteria most adapted to broad spectrum of light found in shallower mixed layer
High Low
Nutrients
Low High
Light Intensity / Irradiance
Deep water / Winter
Shallow water / Summer
Narrow Broad
Light Spectrum
Low High
Temperature

26. Growth-temperature curves vary among species but share upper limit
(Eppley 1972)
Growth rate
Temperature oC

27. Diatoms grow fastest at low temperatures
Flagellates
Divisions per day
Temperature oC

28. Diatoms most adapted to colder temperatures
High Low
Nutrients
Low High
Light Intensity / Irradiance
Deep water / Winter
Shallow water / Summer
Narrow Broad
Light Spectrum
Low High
Temperature

29. Can you explain why production peaks where it does?
Production is
a rate
e.g. [g C m-2 y-1]
Biomass is a
concentration
e.g. [g C m-2]