Carbon dioxide generally dissolves in water. This is why the oceans are responsible for absorbing about 30-50% of the CO2 produced from burning fossil fuels. Cold water is better at dissolving and absorbing gasses like CO2 compared to warmer water, which is why a large amount of it gets dissolved in the ocean’s chilliest waters. This is generally speaking.
Now, with ocean temperatures on the rise, rather than absorbing co2, oceans are beginning to release it. According to Or Bialik, a geoscientist at the University of Münster in Germany, it’s the same thing that happens in a bottle of soda that is carbonated with carbon dioxide. “You usually keep it cold, so the dissolved gasses will stay dissolved. If you leave it in your car for a while and try to open it, all the gasses are going to pop out at once, because when it warms, the capacity of the fluid to hold CO2 goes down.”
With this development, came the formation of carbonate crystals in the Mediterranean Ocean. Experiments done by Bialik and team proved Aragonite, a type of calcium carbonate, was forming abiotically. These crystals are generally used in marine animals as part of their protective shell. However, in addition to the rising sea temperatures creating dissociated crystals, the calcium carbonate within marine shells are simultaneously breaking down as a result of varying pH.
The absorption of carbon dioxide creates carbonic acids, which introduces free hydrogen ions that form with carbonate ions, resulting in fewer carbonate ions for the shells of marine organisms, therefore, these organisms have smaller shells. The ocean’s pH ranges from 7.5 to 8.4, but increasing carbon dioxide levels correlates with a decreased pH, which interferes with marine organisms’ ability to form calcium carbonate shells. Essentially, if the pH is lowered, then the calcium carbonate shells of marine organisms will break down because they act as a buffer to stabilize increasing acidity in the water.
These are interesting, contrasting phenomenons that are further explained in Matt Simon’s Wired Article on the Mediterranean forming carbonate crystals. “As these crystals form, they release CO2. So much so, Bialik calculates, that they account for perhaps 15 percent of the gas that the Mediterranean Sea emits to the atmosphere.
As the sea warms up and loses its CO2, both from the water belching it up and from the proliferating crystals, its acidity actually goes down. This is the opposite process from the one that’s causing widespread ocean acidification: As humans spew more CO2 into the atmosphere, the oceans absorb more of it, and the ensuing chemical reaction raises acidity. Acidification makes it harder for organisms like corals and snails (which are known collectively as calcifiers), to build shells or exoskeletons out of calcium carbonate. But as the Mediterranean warms and releases its absorbed carbon back into the atmosphere, it gets more basic, reversing that acidification.”
For more on this topic visit The Mediterranean Sea Is So Hot, It’s Forming Carbonate Crystals.
For a more in-depth summary on the evaluation of pH, temperature and calcium carbonate breakdown, take a look at my AP Environmental Science lab report: Ocean Acidification Lab
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