1. Introduction: coccolithophores 2. Effects on oceanic chemistry 3. Effects on biology 4....
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Transcript of 1. Introduction: coccolithophores 2. Effects on oceanic chemistry 3. Effects on biology 4....
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1. Introduction: coccolithophores2. Effects on oceanic chemistry 3. Effects on biology4. Discussion and conclusions
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Coccolithophores
• Etymology: carrying round stones• Characteristics:
– Free drifting photosynthetic Phytoplankton (phylum Haptophyta)
– One of the most abundant marine calcifying phytoplankton
– Building of calcium carbonate scales (coccoliths)
Ca2+ + CO32- ↔ CaCO3
Ca2+ + 2HCO3- ↔ CaCO3 + H2O + CO2
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– Favorable conditions cause algae blooms, with a overproduction of coccoliths
– During a bloom the water turns an opaque turquoise (“white waters”)
– Growth is not inhibited by high UV light, such as other phytoplankton species
– Diameter of 5-10 µm
Coccolithophores
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• Occurrence: – Mostly in upper layers of sub polar regions– Nutrient poor and mild temperature waters
Coccolithophores
Satellite image of a bloom in the English Channel off coast of Cornwall (24 July 1999) The Coccolithophore Emiliana huxleyi
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Effects on oceanic chemistry
• Pre-industrial atmospheric [CO2]: 280 ppm• Today atmospheric [CO2]: 380 ppm
CO2 obeys Henry’s law: [CO2](atmosphere) [CO2](surface oceans)
• Dissolution of CO2 into seawater releases hydrogen ions and therefore causes ocean acidification In the past 200 years the oceans absorbed 50% of CO2 emitted by human activities (>500 Gt C02) pH decrease of 0,1 units since pre-industrial times
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Effects on oceanic chemistryOceanic absorption of atmospheric CO2: relevant processes
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Effects on oceanic chemistry
• pH range of seawater: 8,2 ± 0,3 (today)
• Relative proportions of the 3 main inorganic forms of CO2 dissolved in seawater:
- CO2 (aq) (including H2CO3): 1%
- HCO3-: 91%
- CO32-: 8%
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Effects on calcium carbonate and saturation horizons
• Solubility of CaCO3 temperature, pressure (depth): increasing solubility by decreasing temperature and increasing depth
Result of these variables: development of natural boundary in seawater called “saturation horizon”
• Dissolution of CO2 decreases [CO32-], because carbonate
ions react with protons to become bicarbonate (HCO3-)
Equilibrium shifts to the right(Dissolution)
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Effects on calcium carbonate and saturation horizons
• Increasing CO2 levels (and resultant lower pH) of seawater decreases the saturation state of CaCO3 and raises the saturation horizon closer to the surface
• Two main forms of calcium carbonate: aragonite and calcite
Aragonite Calcite
Structure orthorhombic trigonal
Solubility high low
Calcifying species
Corals, pterods, macroalgae
Foraminifera, macroalgae, coccolithophores, crustacea
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Saturation horizon of calcite and aragonite
• Aragonite SH nearer the surface of the oceans because higher solubility than calcite
• Calcifying organisms producing aragonite form of CaCO3 are more vulnerable to changes in ocean acidity
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Ocean acidification vs. chemistry of nutrients and toxins
• Metals exist in two forms in seawater: complex and free dissolved
pH- generally increases the proportion of free dissolved forms (most toxic forms)- release of bound metals from the sediment to the water column- effects on nutrient speciation (phosphate, ammonia, iron, silicate)
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Ocean acidification: past and future
• Ocean acidification is essential an irreversible process during our lifetimes
• Fastest natural change in atmospheric CO2 at the end of the recent ice age:
Δ[CO2]= +80 ppm in 6000 years
Current change occur 100 folder stronger
Changes in ocean pH are outside the range of natural variability They could have a substantial affect on biological processes in the surface oceans
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Effects on biology
• Photosynthesis (POC)
Field
Laboratory
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Effects on biology
• Calcification
Laboratory Field
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Effects on biology
• Calcite/POC
Laboratory Field
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Effects on biology
• Malformation
G. oceanica
780-850 ppm
E. Huxleyi
300 ppm
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Effects on biology
• Negative feedback for atmospheric CO2
Reduced calcification leads to reduced CO2 production from calcification. This results in an increased CO2 storage in the upper part of the ocean.
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Effects on biology
• Also others organisms are affected:
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Effects on biology
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Changing acidity
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Changing acidity
Aragonite saturation of surface waters (light blue: oversaturated, purple: undersaturated)
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Approaches to mitigate ocean acidification
• Addition of alkalinity to the oceans
• Direct injection of CO2 into the deep oceans (CCS-programm: carbon capture and storage)
• Fertilization of the upper oceans with iron
• Preventing accumulation of CO2 in the atmosphere