Plankton and Productivity

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Plankton and Productivity

• Phytoplankton
• Diversity
• Nutrients and light
• Primary production
• New production

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Fig. 1. Examples of representative marine
eukaryotic phytoplankton
P. G. Falkowski et al., Science 305, 354 -360
(2004)
Published by AAAS
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TrichoPicos
Trichodesmium tufts
N2-fixing cyanobacteria (Synechocystis) from
Station ALOHA (10 µm scale bar)
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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
http//www.microscopy-uk.net/micropolitan/index.ht
ml
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Emiliana huxleyi coccoliths
From the E. huxleyi site http//www.soes.soton.a
c.uk/staff/tt/eh//coccoliths.html
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Emiliana huxleyi World
From the E. huxleyi site http//www.soes.soton.a
c.uk/staff/tt/eh/
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Dinoflagellate Diversity (1)
Dinophysis Ceratium http//www.whoi.edu/science/
B/redtide/rtphotos/rtphotos.html
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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 15-18.
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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)

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Marine N Limitation (Ryther Dunstan 1971)
Krebs, Fig. 25.08
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Biolimiting Behavior NO3-
Data eWOCE Line A16. Figure prepared with ODV
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North Atlantic Nutrient Ratios
Data eWOCE. Plot prepared with ODV
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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!

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Nutrient Limitation N vs. P

• The NP ratio of plankton is the same as the NP
  ratio of the deep ocean (Redfield ratio).
• Since N P therefore enter the upper ocean in
  the same proportions as theyre required by
  phytoplankton, why does N appear to be limiting?
• Food webs preferentially export N from the upper
  ocean.

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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)
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P/I Relationship
Lalli Parsons Fig. 3.5
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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.

MannLazier Fig.3.05
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Production vs. Depth
Gulf of Alaska data for May (closed circles)
and September (open circles)
Miller, Fig. 3.9
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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
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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 gt Dmix.

Miller, Fig. 1.3
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New vs. Regenerated Production
modified from http//www.up.ethz.ch/research/nitro
gen_cycle/index
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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!

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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.

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Chl Distribution Atlantic
Composites Sep 97 - Aug 98