1. Introduction: coccolithophores2. Effects on oceanic chemistry 3. Effects on biology4. Discussion and conclusions

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

– 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

• 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

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

Effects on oceanic chemistryOceanic absorption of atmospheric CO2: relevant processes

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%

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)

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

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

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)

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

Effects on biology

• Photosynthesis (POC)

Field

Laboratory

Effects on biology

• Calcification

Laboratory Field

Effects on biology

• Calcite/POC

Laboratory Field

Effects on biology

• Malformation

G. oceanica

780-850 ppm

E. Huxleyi

300 ppm

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.

Effects on biology

• Also others organisms are affected:

Effects on biology

Changing acidity

Changing acidity

Aragonite saturation of surface waters (light blue: oversaturated, purple: undersaturated)

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