Open Oceans: Pelagic Ecosystems II

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Open Oceans Pelagic Ecosystems II
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Measuring Primary Productivity Inferences

• Each direct measures of GPP has disadvantages
• Computer models integrate different parameters to
  estimate rates of productivity through the water
  column and over time
• Model components (Field et al. Science
  281237-240)
• chlorophyll concentration
• water depth in photic zone
• fraction of water column where photosynthesis is
  light-saturated
• surface temperature

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Results of productivity model
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Some patterns

• average primary productivity in the oceans is 50
  g C/m2/yr
• 300 g C/m2/yr considered relatively high rate of
  primary productivity 
• low rates of primary productivity typically 20 to
  30 g C/m2/yr 
• What accounts for this variation?

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Comparing the makeup of water and plankton

• Mean Elemental Ratios of N, and P
• Organisms 16.0N / 1P
• Sea Water 14.7N / 1P
• On average, seawater lacks sufficient organic N
  to take advantage of the available phosphorus

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Limited water mixing further limits nutrient
availability
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Testing models measuring plankton in open oceans

• Techniques for studying plankton consumers
• Plankton levels may be dropping (NASA study)

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Changes in Productivity
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From productivity to food webs A size-based
pelagic food web
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Grazing pressure
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Limits Flows of NPP
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Marine Snow
krill
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A spatially realistic pelagic food web
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What are links among trophic levels in pelagic
systems?
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Large phytoplankton vary with depth
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Nutrient distribution with depth
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Distribution of food web biomass
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The global nitrogen cycle
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Influences on biologically useful Nitrogen
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Diatom mats can migrate vertically
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Consequences of active transport of NO3
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Links to oceanic nekton