1. Plankton and Productivity
Phytoplankton
Diversity
Nutrients and light
Primary production
New production
Georgia Institute of Technology
Biological Oceanography

2. Fig. 1. Examples of representative marine eukaryotic phytoplankton
P. G. Falkowski et al., Science 305, (2004)
Published by AAAS

3. Tricho&Picos Trichodesmium tufts N2-fixing cyanobacteria
(Synechocystis) from Station ALOHA
(10 µm scale bar)

4. Diatom Diversity (4) Top left: Chaetoceros debilis: spiny chain diatom
Bottom left: Ditylum brightwelli
Top right: Coscinodiscus granii
NB: Much of the internal volume of the cell is filled by a vacuole. Strands of cytoplasm can be seen running through the vacuole.
Images from the Microscopy-UK Library:

5. Emiliana huxleyi coccoliths
From the E. huxleyi site:

6. Emiliana huxleyi World
From the E. huxleyi site:

7. Dinoflagellate Diversity (1)
Dinophysis & Ceratium

8. Dinoflagellate Diversity (3)
Citharistes sp. Arrow points to chamber containing cyanobacteria.
Ornithocercus magnificus. Arrow points to girdle list, which contains cyanobacteria. Inset shows epifluorescence image with cyanobacteria fluorescing orange-yellow.
Images from Carpenter 2002 Proc. Roy. Irish Acad. 120B:

9. Phytoplankton Growth Specific growth rate N(t) = Noeµt
N = biomass (cell number, PN, PC, etc.)
µ = specific growth rate (t-1)
Note that µ really reflects the net growth rate
N(t) = Noe(p-r)t
p = specific production rate (t-1)
R = specific respiration rate (t-1)

10. Marine N Limitation (Ryther & Dunstan 1971)
Krebs, Fig

11. “Biolimiting” Behavior – NO3-
Data: eWOCE Line A16. Figure prepared with ODV

12. North Atlantic Nutrient Ratios
Data: eWOCE. Plot prepared with ODV

13. Redfield Ratio
The major nutrients occur in roughly constant ratios in deep water and in plankton.
Nutrients are removed from warm surface waters by plankton and released at depth by biological remineralization of organic matter.
The average ratio of nutrients is called the Redfield ratio after A.C. Redfield.
Biological activity drives the ocean to this state!

14. Nutrient Limitation: N vs. P
The N:P ratio of plankton is the same as the N:P ratio of the deep ocean (Redfield ratio).
Since N & P therefore enter the upper ocean in the same proportions as they’re required by phytoplankton, why does N appear to be limiting?
Food webs preferentially export N from the upper ocean.

15. Light in the Water Column
The deeper you go, the darker it gets…
I(z) = Ioe-kz
Mann & Lazier Fig. 3.05b (left), Miller Fig. 3.3 (right)

16. P/I Relationship
Lalli Parsons Fig. 3.5

17. Stratification and Production
Size of circles reflects intensity of mixing. Note inhibition of mixing by the pycnocline (A & C).
Light decreases exponentially and determines where phytoplankton become light-limited.
Below the euphotic depth, phytoplankton die.
Mann&Lazier Fig.3.05

18. Production vs. Depth
• Gulf of Alaska data for May (closed circles) and September (open circles)
Miller, Fig. 3.9

19. Patterns in Primary Production
Above: Typical annual cycles of primary production. Solid lines show phytoplankton biomass, blue lines show zooplankton biomass.
Left: Schematic of relative abundance of light and nutrients at the sea surface as a function of latitude. Lines show relative seasonal change in primary production at three latitudes.
Lalli & Parsons, Figs. 3.9 & 3.17

20. Riley-Sverdrup Bloom Model
Assumptions
Biomass uniformly distributed
P scales with I
R is constant
Compensation depth (Dc)
P = R for individual phytoplankton.
Critical depth (Dcr)
Community between surface and Dcr in balance.
Blooms occur when Dcr > Dmix.
Miller, Fig. 1.3

21. New vs. Regenerated Production
NH4+
New vs. Regenerated Production
Biological
Pump
modified from

22. Measurement of Primary Production
∆Biomass
Practical difficulties in separating phytoplankton from other components of the ecosystem.
Oxygen light-dark bottle method
The dark bottle measures community respiration.
The light bottle measures net community photosynthesis.
14C Incorporation
The dark bottle provides ambiguous information.
The light bottle measures something near net production.
Long incubations may lead to recycling and equilibration.
Bottle effects may compromise all these approaches!

23. Distribution of Primary Production
Open ocean production dominates the budget despite the low areal rates.
Bottle effects may lead to underestimates in all environments, but especially in the open ocean.

24. Chl Distribution: Atlantic
Composites: Sep 97 - Aug 98