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Chemical Oceanography. Lecture 1: Primary Production Lecture 2: Marine Bio-geochemistry and Sedimentation. Lecture 9: Primary Production. The Reactions of Life, Photosynthesis, Respiration and Growth. Phytoplankton: The Plants of the Ocean

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Chemical Oceanography

Lecture 1: Primary Production

Lecture 2: Marine Bio-geochemistry and Sedimentation


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Lecture 9: Primary Production

  • The Reactions of Life, Photosynthesis, Respiration and Growth.

  • Phytoplankton: The Plants of the Ocean

  • Seasonal Plankton Blooms, Thermoclines and Nutrient Cycling

  • Seeding the Open Ocean, IRONEX

  • Chemosynthesis at Hydrothermal vents


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The Reactions of Life, Photosynthesis, Respiration and Growth.

  • In order to live, grow and reproduce all plants and animals need energy, ultimately there are there are only two sources of energy for life on Earth

  • The Sun – plants have evolved to be able to capture and store the energy in sunlight by photosynthesis

  • Geothermal Heat (residual heat from formation of the Earth and from radioactive decay in the core) – can drive chemosynthesis


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Photosynthesis and Primary Production Growth

  • Biologically driven reactions that cycle carbon dioxide, water and oxygen

    CO2 + H2O + sunlight CH2O + O2

    CH2O + O2  CO2 + H2O

  • Many other elements are required, most importantly Nitrate and Phosphate. These nutrients limit growth in ocean and are found to be absorbed in a very constant rate (Redfield Ratio)

    106 CO2 + 16 HNO3 + H3PO4+ 122 H2O+ sunlight (CH2O)106(NH3)16(H3PO4) + 138 O2


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Nutrients Limit Growth Growth

  • Typical CNP Composition of Ocean Water

    (Redfield Ratio 106 C : 16 N : 1 P)

    C 42400 mg/m3 / 106 = 400 units C

    N 480 mg/m3 / 16 = 30 units N

    P 50 mg/m3 / 1 = 50 units P

  • There is ample C, but N and P will be quickly exhausted.

  • There are many other nutrients and micronutrients: Ca (carbonate shells), Si(silica shells), S, K, Na, Cl, Mg, Cr, Co, Cu, F, I, Fe, Mn, Mo, Se, Zn, Ni, Sn, and V.



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Phytoplankton Growth

  • On land plants are the main primary producers– they need to complex bodies for support and to collect light. e.g. forests, grassland etc.

  • In the oceans seaweeds and corals are similar, e.g. kelp forests. – but limited to coasts

  • In the open ocean there is no need for support and the main primary producers and microscopic plankton.


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Cyanobacteria (blue/green algae) Growth

  • Very simple single-celled prokaryotes, earliest life form on earth. Contain chlorophyll to collect light for photosynthesis, form filaments and mats composed of long chains of cells


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Organic tests – Dinoflagellates Growth

  • Single celled eukaryotes, have a strong organic cuticle, collect light using a red pigment, blooms can produce poisonous ‘red tides’


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Silica tests – Diatoms Growth

  • Single Cell Algae, Use silica to grow a transparent frustules (diatoms)), collect light in green chloroplasts (10 –200 m)


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Silica tests – Radiolaria Growth

  • Single Cell Algae, Use silica to grow a transparent tests (radiolaria), collect light in green chloroplasts (0.5 – 2 mm)


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Calcium carbonate Tests – GrowthForaminifera

  • Use CaCO3 to grow tests. foraminifera ‘farm’ symbiotic dinoflagettes for food, also feed on other plankton e.g. diatoms. (0.5 – 2mm)


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Calcium carbonate Tests – GrowthCoccoliths

  • Use CaCO3 to grow tests. Coccoliths are very small but abundant – Chalk! (~30 m)


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Seasonal Plankton Blooms Growthin Temperate Regions


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The Spring Bloom Growth

  • Increasing light levels and high nutrient levels cause phytoplankton to grow


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Summer – Zooplankton Bloom Growth

  • High light levels, but nutrients low, zooplankton take over from phytoplankton


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The Autumn Bloom Growth

  • Winter mixing starting to break down Thermocline – mixing of nutrients into surface waters



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IRONEX: seeding the ocean Growth

  • The open oceans are areas of low primary production

  • But: light and (N, P) nutrients are available

  • Essential micronutrients such as Fe thought to limit plankton growth

  • IRONEX: will adding Fe to the central Pacific Ocean cause a bloom in Plankton?

  • Oct 1993: Fe(III)citrate and SF6 added to a patch of surface water



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IRONEX and Global CO Growth2

  • Hoped that this experiment might provide a way to ‘cure’ global warming.

  • But: A lot of Fe would be needed

  • 99% of organic matter is recycled in upper ocean, more in deep water

  • Cyanobacteria were stimulated, they have no hard shell and do not sink well

  • Bloom was very short lived

  • Not a practical solution…


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Chemosynthesis at Black Smokers Growth

  • Hydrothermal vents discovered in 1977 by ALVIN submersible

  • Geothermal heat causes seawater to circulates through hot volcanic rocks at MORs

  • Fluids becomes very reducing as sulphide, Fe, Mn, Cu, Au, etc. dissolves

  • When hot waters emerges back into the ocean at vents – the cold seawater causes sulphide minerals to precipitate

  • Builds sulphide mineral chimneys

  • Chemical energy is used by chemoautotrophic bacteria



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Chemosynthesis Growth

  • Without light photosynthesis is not possible

    CO2 + H2O + sunlight CH2O + O2

  • But the bacteria found at black smokers can extract energy from the reaction of hydrogen sulphide from the vents and oxygen in the seawater

    CO2 + H2O + H2S + O2 CH2O + H2SO4

  • Respiration can then proceed as normal

    CH2O + O2 CO2 + H2O

  • This reaction is the basis for the food chain

  • Most species have symbiotic bacteria in their bodies

  • These chemoautotrophs are very ancient and some think this environment could hold key to origin of life





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Mussels Growth



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Fish Growth


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Octopus Growth


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