Biogeochemical Controls and Feedbacks on the Ocean Primary Production

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Biogeochemical Controls and Feedbacks on the
Ocean Primary Production
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Carbon Cycle
Marine Biota
Export Production
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Export Production of Organic Carbon
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Ocean Ecosystem Structure
Trophic levels and dynamics
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Ocean Ecosystem Structure
Example of a more complex Food Web
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Ocean Ecosystem Structure
Energy Transfer between Trophic Levels is not
efficient
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Trophic levels and dynamics
Food Web
Energy
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ENERGY
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How about Mass Transfer?
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How do we measure Biomass?
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Alaska
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Large scale Eddies
200 km
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A useful way to keep track of biomass in the
lower trophic levels is to follow the path of
MACRONUTRIENTS
Carbon C
Nitrogen N
Phosphorus P
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Redfield Ratio
C N P
106 16 1
Redfield A.C., On the proportions of organic
derivations in seawater and their relation to the
composition of plankton. In James Johnson
Memorial Volume. (ed. R.J. Daniel). University
Press of Liverpool, pp. 177-192.
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C N P
source 1) atmosphere
source 1) from N2 atmosphere gas2) ocean
subsurface3) remineralization of dead organic
matter 4) biological (e.g. excretions)
source 1) not biological, not atmospheric2)
fluvial
Nitrogen appears to be the limiting factorin
ocean productivity in todays oceans
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A simplified diagram of an NPZD Ecosystem
Z
P
D
N
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Description of the oceanic ecosystem based on
Nitrogen exchanges
Fixation
N2
Nitrification
Mineralization
NH4
NO3
Uptake
Phytoplankton
Grazing
Mix Layer depth
Chlorophyll
Zooplankton
Mortality
Large detritus
Water column
Susp. particles
Nitrification
N2
NH4
NO3
Denitrification
Aerobic mineralization
Organic matter
Sediment
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A simplified diagram of an ecosystem
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Carbon Cycle
Marine Biota
Export Production
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Export Production of Organic Carbon
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A simplified diagram of an ecosystem
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What are the controls on Export Production?
Nutrient Sources for Primary Production
The fluxed of organic carbon must be sustained by
an adeguate flux of macronutrients If
macronutrients are unavailable then the CO2 flux
is reduced!
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What are the controls on Export Production?

• Ocean nutrient inventory
• 2) Utilization of nutrients in HNLC
• 3) Change Redfield Ratio

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Surface CHL-A
1) Central Gyres
2) Upwelling Regions
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What are the controls on Export Production?

• Ocean nutrient inventory

Nitrogen appears to be the control duringmodern
time. (but was not always this way e.g.
duringlat glacial maxima)
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Modern TIME
N2 fixation
Denitrification
N 25790
N N 16 P (Gruber Sarmiento 1997)
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What are the controls on Export Production?
2) Utilization of nutrients in HNLC
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High Nutrient, Low (Medium) Chlorophyll Regions
Phosphorous
Chlorophyll
Conkright et al., 1994
µm
SeaWiFs

• Why arent the nutrients being completely
  utilized by phytoplankton?

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What are the controls on Export Production?
3) Change Redfield Ratio Do not know much
about this!
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END of Lecture
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Southern Ocean HNLC
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Biologically Mediated Exchange of CO2 Between the
Ocean and Atmosphere
The fluxed of organic carbon must be sustained by
an adeguate flux of macronutrients
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Phytoplankton Blooms
Bands of the dionflagellate Lingulodinium
polyedrum moving onshore over the troughs of a
series of internal waves
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Trophic levels and dynamics
Food Web
Energy
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How about Cyanobacteria?
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Hydrothermal vents and Chemosynthetic bacteria
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