1. Critical and Compensation Depths Spring bloom and seasonal cycle
Geographic variation
Atlantic vs. Pacific
Latitudinal variation

2. 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

3. 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

4. Keep in mind the physics & chemistry of the mixed layer
Wind
Light & Heat
Nutrients

5. Draw the mixed layer here

6. Photosynthesis requires light, Respiration does not
Depth
Depth +
biomass -
biomass
(Requires
light)
(Independent of
light)

7. Compensation Depth P = R Compensation depth R P Depth P>R
Biomass increases
P = R
Compensation depth
P<R
Biomass decreases
Depth

8. Critical Depth GPP=ΣR Net Primary Production (NPP) = 0 Critical depth
R P
Gross Primary Production
(GPP)
Sum of Respiration
(ΣR)
Depth
GPP=ΣR
Net Primary Production (NPP) = 0
Critical depth

9. If critical depth > mixed layer depth, GPP>ΣR, NPP >0
R P
Gross Primary Production
(GPP)
Sum of Respiration
(ΣR)
Depth
Bottom of mixed layer
Critical depth

10. If critical depth < mixed layer depth, GPP<ΣR, NPP<0
R P
Gross Primary Production
(GPP)
Sum of Respiration
(ΣR)
Depth
Critical depth
Bottom of mixed layer

11. Critical depth concept is critical!
Respiration Photosynthesis
Understand why R is a straight line
Understand why P is an exponential curve
Know the difference between:
critical depth
and
compensation depth
Depth

12. 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]

13. 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)

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

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

16. 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).

17. 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
Greek roots:
“auto” =self
“hetero”=other
“troph”=nutrition or to feed
jellyfish
salps

18. 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

19. Seasonal evolution of mixed layer

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

21. 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.

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

23. 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.

24. Atlantic Ocean is saltier than 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.

25. 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

26. Nutrient limitation varies among oceans
Mixed layer is deeper and more nutrient-limited in Atlantic than in Pacific
Remineralized nutrients accumulate in deep water, transported by ocean conveyer belt

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

28. 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

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

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

31. 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.

32. 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)