Ocean acidification
30% anthropogenic CO2 produced in the last 250 yrs has been absorbed in the ocean sink.
Rising temperature reduces ability to absorb.
Tipping point = the critical threshold which leads to irreversible change if passed
Average global surface ocean pH has decreased from 8.2 → 8.1 (30% increase in acidity)
Impacts on marine life:
• Molluscs / crustacea at bottom of food chain unable to build strong shells;
susceptible to predators, reducing biodiversity
• Declining CaCO3 shelled organisms affects C cycle
• Jellyfish thrive in warmer, more acidic conditions. Dominate and disturb ecosystem
equilibrium
• Productive fishing where water upwells with nutrients and CO2 (off the coast of
Peru).
Impacts on fish stocks:
• Larvae vulnerable to acidic water
• Some predatory fish switch prey and show few negative effects
• Other predatory species decline
• Protein dependency up to 50% in LIDCs and EDCs (Gambia, Fiji)
Rising temperatures
Warming oceans and coral reefs:
Corals = marine polyps which live in symbiosis with zooxanthellae algae. Algae release
nutrients by photosynthesis which the polyps feed on and contain pigments which provide
colour.
Conditions:
• 26 degrees
• Salinity 30-32,000 ppm
• Water depth <25m
• Light (clear water)
• Some wave action to oxygenate water
Degree Heating Week = Data collection system by NOAA to show accumulated thermal
stress experienced by coral reefs. 1 DHW = 1 week of sea surface temperatures 1 degree
above expected summer max.
Warming oceans push coral to thermal limit, past this coral bleaching occurs. Salinity
changes increase stress.
Coral bleaching:
Complex process associated with salinity predicted via satellite measurements of sea
surface temperatures and correlated with coral mortality – up to 80% in the Maldives.
Entire coral community bleaching has increased in the past 30 yrs and is evident in the
tropics
