Ocean acidification

Question 1

How is the history of CO2 assessed?

Answer 1

drill cores from the arctic/antarctic

Question 2

Briefly describe the three main CO2 inputs caused by humans?

Answer 2

•2008 Human emissions 10 billion tons ~ 0.2 kg person-1 h-1

~ 8.7 billion tons from fossil fuels + cement production

~1.2 billion tons from deforestation

• Concentrations now higher than for more than 800 000 a
• Industrial era inputs close to 560 billion tons

~ 50 % remains in the atmosphere

~ 25 % removed by vegetation

~ 25 % removed by oceans

Question 3

How does CO2 and reduced pH correlate?

Answer 3

CO2 reduces pH, carbonate ion (CO32-) concentration & alters the saturation states of biologically important CaCO3 minerals

Question 4

How does CO2 behave in surface sea water?

Answer 4

CO2 gas dissolves in seawater (rapid exchange) and creates carbonic acid.

look up slide 7 + 8

CO2 increases H ion concentration -> reduce pH

as H increases carbonate decreases (important for a lot of marine organisms to build their shells)

Net effect: increasing CO2 in the oceans increases H+ (decreases pH) and reduces CO3 2- concentration

Question 5

How is calcium carbonate effected by ocean acidification?

Answer 5

more acid -> concentration of carbonate reduced

-> lower saturation point -> critical for CaCO3 building organisms

Question 6

What is predicted to happen if the drop of pH continues in the oceans?

Answer 6

a drop of pH that has never been that low (as far as we know)

-Spatially variable due to biological activity (production/respiration) and the effects
of seawater properties (T, S) on CO2 solubility (higher in cooler waters)

-Very low saturation values (1 or less) in polar regions, considerably reduced in
tropical regions

Question 7

What are the biological effects of high CO2 contents in the oceans?

Answer 7

• Unlikely terrestrial plants, oceanic primary producers are generally not limited by inorganic carbon sources
• Changes in pH affect gradients across cell membranes affecting physiological performance (photosynthesis, respiration, growth), availability of trace elements
• Many organisms secret CaCO3 skeleton/shells
• Decreased CO3 reduces saturation state

Currently oceanic  > 2-6 (supersaturated)
• HOWEVER many marine organisms are adapted to a pre-industrial ocean
so have optimal precipitation rates at supersaturated states
• Research in its infancy - really have little idea of the ecosystem-wide affects,

Question 8

Why would it be devastating if calcification would become more difficult for oceanic organisms?

Answer 8

• Calcification is energetically expencive -> organisms would have to invest more energy to build structures less strong
• small changes in saturation impact calcification rates and modify crystal structure
• many key species are calcifying organisms
• However, difficult to predict changes but acidification will reduce resilience making systems more prone to ecosystem shifts*

Question 9

Give an example of how acidification alters key species interactions

Answer 9

• snail produces thicker shell when exposed to chemical cues from crabs
• when pH was reduced, no shell thickening was observed
• compensated with increased movement -> decreased foraging time
• key biological interactions regulate ecosystem function

We simply don’t know enough about organisms physiology, interactions among species and with their environment to predict affects sufficiently

Question 10

Which oceans are believed to undergo the greatest changes due to acidification?

Answer 10

Polar Oceans

• cold temperatures increase CO2 solubility
• saturation states naturally much lower then temperate and tropical regions
• Many key pelagic and benthic species are calcified which are important food sources for higher order predators
• impact accelerates due to the loss of sea ice (more ocean exposed to atmosphere)