evsc week 9: Ocean Acidification

Identify the control variables ocean acidification.

Average global surface ocean saturation state with respect to aragonite (Ω).

Identify the planetary boundaries for ocean acidification.

>80% of the pre-industrial aragonite saturation state of mean surface ocean (including natural and seasonal variability).

current status of ocean acidification

about 84% of the pre-industrial aragonite saturation state, meaning the boundary has not yet been crossed, but we are close.

how the ocean acidification boundary is linked with climate change

Both are driven by excess atmospheric CO2. Increased CO2 warms the climate (climate change boundary) and lowers ocean pH (ocean acidification boundary).

how the ocean acidification boundary is linked with biosphere integrity boundaries

Coral reefs and other marine organisms depend on CaCO3 for their shells and skeletons. Ocean acidification threatens these organisms, directly impacting marine biodiversity and ecosystem function, which ties to the biosphere integrity boundary.

Describe carbon dioxide dissolution and solubility (and their chemistry) in the context of the ocean carbon system

1. CO2 (atmosphere) ↔ CO2 (aqueous)

2. CO2 (aq) + H2O ↔ H2CO3 (carbonic acid)

3. H2CO3 ↔ HCO3⁻ + H⁺

4. HCO3⁻ ↔ CO3²⁻ + H⁺

5. CaCO3 ↔ Ca²⁺ + CO3²⁻

6. CO3²⁻ + H⁺ ↔ HCO3⁻

basic idea of the steps - memorize

1 molecule of CO2 (atmospheric) interacts with 1 molecule of H2O, resulting in 1 molecule of CO3 2- and 2 molecules of H+.

• Some of these newly available H+ ions re-combine with CO3 2- to produce HCO3 - (buffering).

• However, some of the CO3 2- used in this buffering process comes from the CaCO3 used by marine organisms.

• Therefore, the addition of CO2 drives the dissolution of CaCO3 .

Explain how the ocean carbon system buffers the ocean against rapid changes in seawater pH

• Added H⁺ from CO2 dissolution can react with carbonate ions to form bicarbonate.

• Bicarbonate can release H⁺ if pH rises.

  • This buffering slows pH changes, but is not unlimited; continued CO2 emissions reduce available carbonate, harming calcifying organisms.

Describe geographic differences in ocean acidification using maps

• Polar regions: More acidic; colder waters dissolve more CO2 → higher acidification.

• Tropics: Less acidic; warmer waters dissolve less CO2 → smaller pH change.

• Implication: Ocean acidification is spatially variable, meaning some ecosystems are more vulnerable than others.

impacts of ocean acidification on humans

• Threatens coral reefs, which support 25% of marine species.

• Reduces populations of shellfish, clams, oysters, lobsters, and crabs – affecting fisheries and food security.

• Economic impact on tourism and coastal protection (reefs act as natural barriers against storms).

• Potential biodiversity loss, affecting marine ecosystem services humans rely on.

List solutions to the ocean acidification issue

• Primary solution: Reduce CO2 emissions (same as for climate change).

• Secondary approaches (supportive):

  • Protect and restore coral reefs and marine ecosystems.

  • Support research on carbon capture and storage technologies.

  • Monitor ocean pH and aragonite saturation to guide adaptive management.

• Key insight: Under a low-emissions scenario (RCP2.6), ocean pH can start to recover by ~2050.

what does the amount of CO2 depend on

depends on partial pressure and how soluble it is - that’s why it’s linked to climate change