Unit 03 Chemical Equilibrium
Wolfe, W. H., Martz, T. R., Dickson, A. G., et al. (2023). A 37-year record of ocean acidification in the Southern California current. Communications Earth & Environment, 4, 406.
Read The Original ArticleThis is an open-access research article examining a 37-year record of ocean chemistry.
The purpose of this study was to investigate long-term changes in seawater chemistry associated with ocean acidification. Researchers analyzed measurements from the California Cooperative Oceanic Fisheries Investigations program. The dataset included decades of measurements of seawater inorganic carbon chemistry. Using variables such as total alkalinity and dissolved inorganic carbon, the researchers examined changes in pH, carbon dioxide, carbonate ions, and calcium-carbonate saturation.
The researchers found a clear long-term acidification trend at the study site. From 1984 to 2021, surface-water pH decreased by approximately 0.0015 ± 0.0001 pH units per year. The researchers also observed seasonal changes influenced by temperature and dissolved inorganic carbon. The study concluded that long-term measurements are extremely important because regional ocean chemistry may behave differently from broad global predictions. The results provide direct evidence that ocean carbonate chemistry is changing over time.
When more atmospheric CO₂ enters the ocean, the concentration of dissolved CO₂ increases. According to Le Châtelier's principle, an equilibrium system responds to an imposed change. The connected carbonate equilibria respond in ways that ultimately increase the concentration of H⁺ ions.
Because the pH scale is logarithmic, a seemingly small numerical pH change still represents a significant chemical change in hydrogen-ion concentration.
pH = −log[H⁺]
Marine organisms such as corals and some shell-forming organisms use calcium carbonate. Changes in carbonate-ion availability can therefore affect calcium-carbonate formation. The study's measurements included carbonate-related variables and calcium-carbonate saturation states.
Ca²⁺(aq) + CO₃²⁻(aq) ⇌ CaCO₃(s)
Step 1
CO₂(g) ⇌ CO₂(aq)
Atmospheric CO₂ enters the ocean.
Step 2
CO₂(aq) + H₂O(l) ⇌ H₂CO₃(aq)
Dissolved carbon dioxide reacts with water.
Step 3
H₂CO₃(aq) ⇌ H⁺(aq) + HCO₃⁻(aq)
Carbonic acid produces hydrogen ions.
Step 4
HCO₃⁻(aq) ⇌ H⁺(aq) + CO₃²⁻(aq)
Another equilibrium exists between bicarbonate and carbonate ions.
Catholic Graduate Expectation
Ocean acidification demonstrates that chemical changes can connect people and ecosystems across the world. Carbon dioxide released in one location does not necessarily remain there. The atmosphere and oceans form interconnected global systems.
This creates an ethical responsibility to consider how human activity affects ecosystems and future generations. Changes in ocean chemistry can affect organisms, biodiversity, fisheries, and communities that depend on marine ecosystems.
A responsible citizen uses scientific evidence when making environmental decisions. Protecting ocean ecosystems reflects stewardship of creation and recognizes that environmental resources should be protected for both present and future generations.
Key Takeaway
Ocean acidification is a real-world demonstration of Le Ch\u00E2telier's principle because increasing CO\u2082 changes several connected chemical equilibria in seawater.