Ocean pH and Acidification Quiz

Ocean pH & Acidification

• The pH scale is logarithmic, meaning a 0.1 decrease in pH represents a 30% increase in acidity.
• Pre-industrial levels of acidity increased by 16% by the year 2100.
• By 2100 there will be a decrease of 0.3 to 0.4 units in pH, a 100-150% increase in acidity, and a 50% decrease in carbonate ion levels.
• Ocean water is slightly alkaline, but this alkalinity decreases with depth.
• Upwelling brings lower pH surface waters to the surface.
• pH is defined as the negative logarithm of hydrogen ion concentration.
• Increasing CO2 in seawater lowers ocean pH.

Chemical Reactions

• Carbon dioxide (CO2) dissolved in seawater reacts with water (H2O) to form carbonic acid (H2CO3).
• Carbonic acid dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3−).
• Hydrogen ions increase, driving down pH and making the water more acidic.
• Carbonate ions (CO32-) are formed, making the water more alkaline.

Carbonate Saturation Depth

• Ocean acidification impacts the carbonate saturation depth.
• The saturation depth is the depth at which the concentration of carbonate ions is low enough for calcium carbonate to dissolve.
• Ocean acidification decreases the carbonate ion concentration, causing this depth to occur shallower in the water column.

Impacts on Biological Organisms

• Organisms that produce calcium carbonate shells or skeletons are most affected by ocean acidification.
• Calcification responses vary among organisms.
• Some crustaceans, urchins, certain algae, and corals are affected by decreasing Ω (saturation state), while shellfish also show some impacts.
• Ecological implications of these impacts are not yet fully understood.

Impacts on Food Webs and Fisheries

• Ocean acidification impacts the lower levels of the food web (e.g., coccolithophores, pteropods, and copepods).
• If organisms at the lower trophic levels cannot survive, it will have negative impacts up the food web to species, such as Pacific Salmon.
• Valuable commercial fisheries depend on species that are sensitive to ocean acidification.
• Predators that feed on calcifiers are also impacted when the food source is impacted.

Future Estimates

• Increased atmospheric CO2 levels are projected to cause ocean acidification.
• Ocean pH will decrease by 0.3−0.4 units in the coming decades.
• Ocean acidity is expected to increase by 100-150% by 2100.
• Carbonate ion concentration will decrease by 50%.

Potential Impacts on Fisheries

• Valuable fisheries depend on commercial, shellfish, and predator species that feed on calcifiers.
• Commercial landings and values for U.S. commercial fisheries were down 5.3% in 2018.
• Estimated values of the major fish species in this industry are also decreasing.