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The Role of Temperature
  • Temperature directly influences metabolic rates; rates double with 10°C temperature increase (Q10) 

  • Sea surface temperature: 
    • Tropical: 25 °C
    • Subtropical: 15 °C
    • Temperate: 5 °C (northern limit) 2 °C (southern limit)
    • Polar: <0-2 °C or 5 °C

  • Temperature also stabilizes the water column during summer and prevents phytoplankton being mixed to greater depths (less or no light!)
  • Main gradient in temperature = thermocline; deep in winter, more shallow during summer, deepens in fall again

  • Photosynthesis

    • The formation of organic matter from inorganic carbon (CO2) with light as the primary energy source
    • 6 carbon dioxide + 6 water = 1 glucose + 6 oxygen 

    • 6 CO2 + 6 H20 = C6H12O6 + 6 O2
    • Two reaction steps: 
      • (1) Light reaction: photophosphorylation: production of O2 and energy from H2

      • (Where does the O2 come from, H2O / CO2?) 
      • (2) Dark reaction: carbon fixation: CO2 to glucose
    • Phytoplankton and algal photosynthesis = primary production
    • Organisms that perform photosynthesis = primary producers = autotrophic = phototrophic organisms
    • All phototrophic organisms possess chlorophyll a and several accessory pigments (chl. b, c, carotenoids), which serve as antenna pigments to capture light energy and transfer electrons to the photosynthetic reaction center
    • Each pigment has a distinct absorption spectrum 
    • Photosynthesis most efficient in blue and red light, according to absorption maximum of chlorophyll (action spectrum)
      Light in Lakes and Oceans

Blue light containes more energy per proton than red light
  • 280 – 320 nm: UV-B
  • 320 – 400 nm: UV-A
  • 400 – 700 nm: PAR – Photosynthetically  Active Radiation
  • > 700 nm: IR (Infrared Radiation)
  • Light decreases exponentially with depth
  • Blue light penetrates deepest into the ocean, red light is absorbed fastest (Consequences: Live seems more ‘colorless’ with depth)
    • Optical classes of water (Jerlov):
    • Coastal oceans: stronger light absorption, brownish to greenish due to shift in spectral absorbance
    • Open oceans: clearest water, deep euphotic zone, blue color
      Photosynthesis and Light
    • P vs. I curves (photosynthesis versus light intensity): shows photosynthetic adaptation
    • Gross production = total production; net production = gross prod. – respiration
    • Compensation point: photosynthesis = respiration, 

    • net production = 0
    • Pmax = maximum production; depends on dark reaction (unlimited growth) or limiting resources
    • Initial slope a: photosynthetic efficiency (how good is low light used), also quantum yield f = D P/DI; depends on light reaction
    • Ik: summarizes key characteristics Pmax and a in one term; shade-adapted cells have lower Ik than high-light cells


    Note: Species (1) and (2) have the same Ik despite different Pmax and a. The lower Ik of (1) and (2) as compared to (3) reveals them as shade-adapted species.

    The depth of maximum phytoplankton abundance is a compromise between light and available nutrients; often near the thermocline

    Blown with the winds: Turbulence and upwelling

Water movements by wind and currents affect plankton distributions 
  • Langmuir circulation: lines of concentrations

  • Wind-driven surface flows

  • Eddy formation: Gulf Stream rings

  • Coastal upwelling: Eckman transport