By: Meg Xu
As the human population increases alongside a continued reliance on fossil fuels the ocean faces increased tension. One of the major carbon sinks of the world and the simultaneous host of various complex ecosystems, the ocean is critical to life on earth. Facing increased acidity/decreased pH the ocean faces various problems as carbon emissions continue skyrocketing.
As carbon dioxide dissolves into our oceans it becomes aqueous. This carbon dioxide then reacts with water to form carbonic acid. This highly unstable acid dissociates into bicarbonate and then carbonate. In doing so excess H+ ions are added to the ocean which increases the acidity and decreases the pH.
CO2(g)CO2(aq)
CO2(aq)+H2O(l)H2CO3(aq)
H2CO3(aq)H++HCO3(aq)-
HCO3(aq)-H++CO3(aq)2-
Ocean acidification has comically been called “climate change's equally evil twin”, epitomizing the extent to which this issue has impacted our world. Since the industrial era 525 billion tons of CO2 have been absorbed by the atmosphere– 22 million tons daily. Due to this air pollution our oceans have become 30% more acidic in just the last 200 years. This is a faster change in acidity than what the earth has witnessed in the last 50 million years.
In addition excess H+ ions react with calcium carbonate, an essential component of marine organisms shells. This reaction forms calcium chloride and carbonic acid which then dissociates into more H+ ions.
H++CaCO3(s)H2CO3(aq)+CaCl2(aq)
H2CO3(aq)H++HCO3(aq)-
HCO3(aq)-H++CO3(aq)2-
By 2080 waters will be too acidic for the survival of any coral reefs as carbonate is essential to the building of reefs. A model by Mollica et. al predicts an average 12. 4+/-5.8% decline in coral reefs in the 21th century from acidification alone. This model demonstrates causation between acidity and coral decline as the largest decreases in skeletal density (11.4–20.3%) was driven by the largest pH decreases projected for this region (up to 0.35 units) while reefs with little density decrease were in regions of minimal pH change.
Overall, ocean acidification is a huge issue in our modern world. Despite the chemical complexities of understanding this issue we should not let that deter us from taking action.
Sources:
https://theotherco2problem.wordpress.com/wp-content/uploads/2009/11/ocean-chemistry.gif
https://ocean.si.edu/ocean-life/invertebrates/ocean-acidification
https://ocean.si.edu/conservation/acidification/ocean-acidification-graph
https://mindthegraph.com/blog/ocean-acidification-consequences/
https://www.scientificamerican.com/article/corals-are-dissolving-away1/
