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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
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
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
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
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.
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.
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
Organic tests – Dinoflagellates • Single celled eukaryotes, have a strong organic cuticle, collect light using a red pigment, blooms can produce poisonous ‘red tides’
Silica tests – Diatoms • Single Cell Algae, Use silica to grow a transparent frustules (diatoms)), collect light in green chloroplasts (10 –200 m)
Silica tests – Radiolaria • Single Cell Algae, Use silica to grow a transparent tests (radiolaria), collect light in green chloroplasts (0.5 – 2 mm)
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)
Calcium carbonate Tests – Coccoliths • Use CaCO3 to grow tests. Coccoliths are very small but abundant – Chalk! (~30 m)
The Spring Bloom • Increasing light levels and high nutrient levels cause phytoplankton to grow
Summer – Zooplankton Bloom • High light levels, but nutrients low, zooplankton take over from phytoplankton
The Autumn Bloom • Winter mixing starting to break down Thermocline – mixing of nutrients into surface waters
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
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…
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
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
