There is one good thing that has come out of Covid. With no tourists causing extra wastewater pollution, sunbathing or swimming off beaches, we are witness to the health of coral reefs and coastal marine ecosystems recovering all around the world. There are a number of reasons for this, and one of them is particularly surprising. We don’t immediately think of cosmetics or sunscreens being toxic to marine life, but the reality is remarkably different.
Many of our cosmetics contain an ingredient called oxybenzone. It is used in products to protect us from the damaging effects of UV light from the sun. Sunblock is probably the wrong name for this cosmetic ingredient, because oxybenzone does not block UV light, it just changes it to a longer, less energetic wavelength that is safer for human skin. But, in changing the wavelength free radicals are released that are really dangerous, especially to corals, algae and plankton, and to a lesser degree, people. The chemical itself is relatively non-toxic, but the way in which it reacts with sunlight, plastic particles and nature makes it just about the most toxic chemical on the planet.
Carbon dioxide in the atmospheres dissolves into seawater to form an acid, and this drops the pH (acidity) of the seawater. There are lots of studies on pH and the pH stability of seawater; it is very well understood chemistry, but in basic terms, the higher the alkalinity the lower the solubility of calcium carbonate, and the more stable the pH.
From the BIOACID group’s work  their data demonstrated for us that a stunning 30% to 50% of Mollusca, Corals, Echinoderms, calcifying macro algae and tropical species are negatively impacted (reproduction) at a pH between pH7.97 to pH8.05. Let’s be clear – Oceanic pH is currently 8.05 and its on its way down and the remaining 50% Corals are already screaming out for help. Coral reefs are incredibly important ecosystems, because along with their symbiotic algae, they cover less than 3% of the Earth’s seabed, but they are the nursery ground for 25% of all marine life. Coral reefs are also totally dependent on what happens to pelagic plankton in the oceans off-shore, and 0.5 billion people depend directly on corals and their fish communities as a source of food, and for their economy. In fact, the very existence of many island and coastal communities depends upon coral reefs. We could potentially lose more than 80% of the world’s coral reefs over the next 10 years.
Why does that matter? Well, we know that the current rate of acidification is over 10 times faster than any time in the last 55 million years, and that during the late Cretaceous period (70 million years ago), ocean chemistry was completely different, with calcium alkalinity five times higher and magnesium concentrations much lower.
This really matters, because our oceans have now flipped this calcium/magnesium balance, and now have low calcium
alkalinity, and high magnesium concentrations. This change in chemistry makes our oceans much more susceptible to change (acidification) and calcium in the form of aragonite dissolves at a higher pH. Magnesium salts are much more soluble than calcium, so the high magnesium concentrations mean that the shells and skeletons of most marine life become more soluble.
In the Cretaceous period, ocean pH was around pH7.5 but remember this was 70 million years ago (when the calcium was high, and magnesium was low) and carbon dioxide concentrations in the atmosphere were actually three times higher and Arctic temperatures 15°C warmer than they are today. But there were no mass mortalities, and the oceans were incredibly productive. Today, ocean chemistry change means they are now 50 times more sensitive to carbon dioxide and acidification because of the drop in calcium alkalinity and the increased concentration of magnesium.
Taking all of the above into account, the GOES Foundation team have concluded that the oceanic tipping point is a pH of 7.95 which we reach by 2045/50 under RCP 8.5 from the IPCC. In the southern oceans it could be 10 years earlier, they are the most productive oceans on the planet, but we could see their collapse by 2035 and this will have ramifications all around the world. Ecosystems will start crashing  and ocean currents will stop or change direction – the Gulf stream has already slowed down by 15%. We may lose the planktonic plants that are the life support system and climate regulator for our planet – it will be run-away climate change. Cyanobacteria, protists and jellyfish will take over the oceans, and may help sequester carbon, but we expect the oceans to become a toxic soup as a consequence.
Dryden H., Duncan D., Brown S. T. & Miranda H., 2021. How to save the oceans and fight climate change. Goes Foundation. Full report.