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Introduction: coccolithophores Effects on oceanic chemistry Effects on biology

Introduction: coccolithophores Effects on oceanic chemistry Effects on biology Discussion and conclusions. Coccolithophores. Etymology: carrying round stones Characteristics: Free drifting photosynthetic Phytoplankton (phylum Haptophyta)

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Introduction: coccolithophores Effects on oceanic chemistry Effects on biology

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  1. Introduction: coccolithophores • Effects on oceanic chemistry • Effects on biology • Discussion and conclusions

  2. 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

  3. Coccolithophores • 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

  4. Coccolithophores • Occurrence: • Mostly in upper layers of sub polar regions • Nutrient poor and mild temperature waters Satellite image of a bloom in the English Channel off coast of Cornwall (24 July 1999) The Coccolithophore Emiliana huxleyi

  5. 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 Effects on oceanic chemistry

  6. Effects on oceanic chemistry Oceanic absorption of atmospheric CO2: relevant processes

  7. 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%

  8. 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)

  9. 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

  10. 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

  11. 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)

  12. 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

  13. Effects on biology • Photosynthesis (POC) Laboratory Field

  14. Effects on biology • Calcification Laboratory Field

  15. Effects on biology • Calcite/POC Laboratory Field

  16. Effects on biology • Malformation E. Huxleyi G. oceanica 300 ppm 780-850 ppm

  17. 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.

  18. Effects on biology • Also others organisms are affected:

  19. Effects on biology

  20. Changing acidity

  21. Changing acidity • Aragonite saturation of surface waters (light blue: oversaturated, purple: undersaturated)

  22. 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

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