1. Competition for nutrients Major phytoplankton groups Light
Review
Competition for nutrients
Major phytoplankton groups
Light
Critical and Compensation Depths
Spring bloom and seasonal cycle
Geographic variation
Atlantic vs. Pacific
Latitudinal variation

2. Competition for nutrients
μmax1 = μmax2
Ks1<Ks2
μmax2 > μmax1
Equal Ks
Species 1
Species 2
Specific Growth Rate μ
Max growth rate
(a constant)
Half-saturation constant
Nutrient Concentration N

3. Light Intensity / Irradiance
Diatoms
Dinoflagellates
Coccolithophores
Cyanobacteria
High Low
Nutrients
Low High
Light Intensity / Irradiance
Narrow Broad
Light Spectrum
Temperature
Deep water / Winter
Shallow water / Summer

4. Light attenuates exponentially with depth.
Longer wavelengths have greater absorption by particles and attenuate more with depth.
Too much light damages cells and reduces photosynthesis (photoinhibition).
depth
Irradiance

5. Compensation & Critical Depth

6. Video of mixed layer with wind mixing (go to 8:21)

7. Spring bloom in satellite images
NASA/Goddard Space Flight Center, The SeaWiFS Project and GeoEye, Scientific Visualization Studio. NOTE: All SeaWiFS images and data presented on this web site are for research and educational use only. All commercial use of SeaWiFS data must be coordinated with GeoEye ( Data provided by: Norman Kuring (NASA/GSFC)

8. Need to add zooplankton to understand seasonal cycles
Phytoplankton
Physical mixing
processes
Nutrients
Irradiance
Zooplankton

9. Definitions
Phytoplankton
Phyto- (plant) and planktos (drifter)
drifting single-celled algae
Zooplankton
Zoo- (animal) and planktos (drifter)
Small drifting animals

10. Definitions
Autotrophs get their carbon and energy from inorganic sources. Phytoplankton are autotrophs because they get their carbon from CO2 and energy from light.
Heterotrophs get their carbon and energy from pre-formed organic matter. Zooplankton are heterotrophs because they get carbon and energy by eating phytoplankton (or zooplankton).

11. Some marine heterotrophs (Zooplankton)
Protists - single cells
Size range: 1 to 1000 μm
Life span: days to ~week
Crustaceans
Size range: 0.01 to 10 cm
Life span: weeks to years
Gelatinous animals
Size range: mm to m
Life span: months to ~year
ciliates
dinoflagellates
Copepods are the most numerous multicellular marine animals!
krill
copepods
jellyfish
salps

12. Generation times differ
Phytoplankton
Reproduce by dividing
~ hours to days
Limited by:
Nutrients, light, temperature
Zooplankton
Several life stages
~2-4 weeks
Limited by:
Food availability, temperature

13. Seasonal evolution of mixed layer

14. Annual cycle in N. Atlantic
Nutrients
Light Temperature
Mixing
Mixing
Relative increase
Stratified

15. Annual cycle in N. Atlantic
Nutrients
Light Temperature
Mixing
Mixing
Stratified
Relative increase
Spring
bloom
Fall mini-
Phytoplankton biomass
Zooplankton biomass
This mechanism of bloom formation is described by Sverdrup’s “Critical Depth” hypothesis.

16. Draw seasonal cycle of temperate and light profiles with critical depth here

17. Need Dcr>Dm for NPP>0
Early spring
diatoms,
dinos
Late spring
coccoliths
Plankton
0-100 m
(# per L)
2-3 week
delay in bloom
of copepods
These are the data underlying Sverdrup’s “critical depth” hypothesis.
Depth (m)

18. Primary production and its seasonal cycle vary greatly in space
Chl a from SeaWIFS satellite
Nutrient sources to surface waters are:
rivers and land runoff
upwelling
atmosphere
The most productive regions of the oceans are the coastal regions because this is where upwelling is strongest and where river and land runoff meet the sea. Here nutrients result in high productivity rates, which in turn result large fisheries.

19. Mixed layer is deeper in Atlantic than in Pacific
Atlantic Ocean
Depth (m)
South pole Equator North Pole
Pacific Ocean
The surface N. Atlantic is saltier than the surface N. Pacific, making surface water denser in the N. Atlantic at a given temperature. This difference is because on average N. Atlantic is warmer than N because local heating from the Gulf Stream. Warmer water evaporates faster, leaving higher-salinity water.
Depth (m)
South pole Equator North Pole
Temperature

20. Atlantic Ocean is saltier than Pacific Ocean

21. Nutrient limitation varies among oceans
Mixed layer is deeper in Atlantic than in Pacific
Remineralized nutrients accumulate in deep water, transported by ocean conveyer belt

22. Draw Atlantic vs. Pacific mixed layer depths

23. Atlantic vs. Pacific mixed layer depths
Time (month)
Dcr
Dm (Atl.)
Dm (Pac.)
NPP>0
NPP>0

24. Atlantic vs. Pacific spring bloom
Winter:
Deep mixed layer,
Production shuts down
Spring:
Phytoplankton bloom
Zooplankton - slow to catch up
Winter:
Shallower mixed layer,
Continuous low production
Spring:
Phytoplankton bloom
Zooplankton - right there
to eat the bloom!
Phytoplankton biomass
Zooplankton biomass

25. Latitudinal variation in seasonal cycles driven by variation in irradiance
[Also Irradiance]
90oN = N. Pole
60oN ~Anchorage,AK
30oN ~N. Florida
0oN = Equator

26. Seasonal cycle varies with latitude
Nutrients
Light
[Nutrient]
Latitude
Light
Winter Spring Summer Autumn Winter
Lalli & Parsons

27. Annual cycles in other regions
Phytoplankton biomass
Zooplankton biomass
Try this on your own: Draw the vertical profiles of temperature and light and the critical depth for each region as we did in class for the North Atlantic.

28. This time watch the Arctic and equator
NASA/Goddard Space Flight Center, The SeaWiFS Project and GeoEye, Scientific Visualization Studio. NOTE: All SeaWiFS images and data presented on this web site are for research and educational use only. All commercial use of SeaWiFS data must be coordinated with GeoEye ( Data provided by: Norman Kuring (NASA/GSFC)

29. Spring bloom mechanism
Critical depth hypothesis – Sverdrup 1953
(this is the one we’ve been talking about)
Recent alternative hypotheses:
-Dilution recoupling hypothesis – Behrenfeld 2010
-Stratification onset hypothesis – Chiswell 2011
-Shutdown of turbulent convection hypothesis – Taylor and Ferrari 2011

30. Phytoplankton Irradiance
Physical mixing
processes
Nutrients
Irradiance
Zooplankton
Higher Trophic Levels
Sinking & Senescence
Particle Dynamics
Particle Flux (Carbon flux)