Lecture 11

• Oceans absorb more and more CO2, becoming increasingly acidic - happening at an unprecedented rate
• Solubility cycle: allows the ocean carbon cycle to buffer against changes in pH - but cannot buffer all of it hence leading to a global decrease in ocean pH
• Ocean acidification is more pronounced in northern oceans because CO2 is more soluble in cold water
• How does Ocean Acidification impact biodiversity

  • drops in metabolic rate of organisms
  • drops in immune response to other organisms like parasites or bacteria e.g. Hypercapnia
  • drop in the number of calcium carbonate ions available - issues for corals, molluscs and crabs
  • single-celled organisms that are close to the food web and important to renew ecosystems are affected by pH e.g. coccolithophores - could results in smaller cloud cover and reduce reflectivity of Earth
• Pteropods in PNW: "sea butterflies" that provide food for salmon, herring and other fish - evidence of shells being dissolved/highly damaged

  • more energy needed to maintain and repair their shells
  • decreased ability to avoid predators
  • metabolic effects concerning growth rate, maturity and reproduction
  • increased physiological stress
  • affects food web
• Coral reefs: large, underwater structures formed by groups of small invertebrates that produce calcium carbonate exoskeletons, which accumulate over time
• Control variable: Carbonate ion concentration, average global surface ocean saturation state with respect to aragonite

  • Current value: - 84% of pre-industrial aragonite saturation rate
• Planetary boundary: >or= 80% of pre-industrial aragonite saturation state of mean surface ocean, including natural and seasonal variability
• Saturation rate (Omega): describes the level of saturation of calcium carbonate in seawater. The mineral form of calcium carbonate is called aragonite

  • Omega < 1 - corrosive (undersaturated) for aragonite-based shells and skeletons
  • Omega > 1 - waters are supersaturated with respect to calcium carbonate and conditions are favourable for shell formation
  • Omega > 3 - coral growth benefits (Best)
• Solutions:

  • restore/establish land uses that enhance uptake of atmospheric CO2 by vegetation and soils e.g. wetland restoration
  • Geoengineering? - e.g. fertilising oceans with iron to cause human-made phytoplankton blooms to take up CO2 - only in some areas, detrimental effects unknown
  • cut fossil fuel emissions