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Chemical Oceanography

Chemical Oceanography

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Chemical Oceanography

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  1. Chemical Oceanography Lecture 1: Primary Production Lecture 2: Marine Bio-geochemistry and Sedimentation

  2. 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

  3. 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

  4. Photosynthesis and Primary Production • 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

  5. Nutrients Limit 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.

  6. World Primary Production

  7. Phytoplankton • 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.

  8. Cyanobacteria (blue/green algae) • 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

  9. Organic tests – Dinoflagellates • Single celled eukaryotes, have a strong organic cuticle, collect light using a red pigment, blooms can produce poisonous ‘red tides’

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

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

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

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

  14. Seasonal Plankton Blooms in Temperate Regions

  15. The Spring Bloom • Increasing light levels and high nutrient levels cause phytoplankton to grow

  16. Summer – Zooplankton Bloom • High light levels, but nutrients low, zooplankton take over from phytoplankton

  17. The Autumn Bloom • Winter mixing starting to break down Thermocline – mixing of nutrients into surface waters

  18. Total Annual Biomass Production

  19. IRONEX: seeding the ocean • 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

  20. Chlorophyll Increase

  21. IRONEX and Global CO2 • 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…

  22. Chemosynthesis at Black Smokers • 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

  23. Known Black Smoker locations

  24. Chemosynthesis • 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

  25. Chemoautotrophic Bacteria

  26. Tube Worms

  27. Giant Calms

  28. Mussels

  29. Spider Crabs

  30. Fish

  31. Octopus