A Stormy Ocean off the coast of Fort Matanzas National Monument
Ocean Acidification
All the world’s oceans are physically connected and together cover about 71% of the Earth’s surface and collectively contain perhaps 352 quintillion gallons of water. The world ocean is the predominant natural feature on the planet, and one would think it would prove impervious to the actions of just one living species. And yet, it is no secret that the oceans are overfished and polluted with the byproducts of human civilization. (Microplastics, the degraded remnants of larger plastic items, are now found in surface waters throughout the globe.) Bad enough, but could the very chemistry of the oceans be changing due to humanity’s influence? The answer is yes.
It is well documented that excess carbon dioxide pumped into the atmosphere since the beginning of the Industrial Revolution has warmed the atmosphere and (along with other greenhouse gases) is responsible for a changing worldwide climate. What may be less appreciated is that every year about a quarter of the CO-2 released into the atmosphere is absorbed by the oceans. In fact, it is estimated by scientists at the National Oceanic and Atmospheric Administration and the Smithsonian Institution that the oceans have absorbed around an excess 525 billion tons of carbon dioxide since 1760 (or currently around 22 million tons per day)!
When carbon dioxide and water mix, the result of their union is carbonic acid. In pre-industrial times, natural CO-2 in the atmosphere combining with ocean water maintained an ocean alkalinity of 8.2 on the pH scale. Since industry began in earnest that figure has fallen to 8.1 units. That may not seem like a lot, but keep in mind the pH scale is logarithmic. For example, pH 4 is ten times more acidic than pH 5, and 100 times more acidic than pH 6 (10 x 10). So a decrease of .1 pH units represents a 30% decrease in alkalinity. (pH 7 is considered neutral, with numbers less than that increasingly acidic, and numbers greater increasingly alkaline, or basic.) The term for the ocean becoming steadily less alkaline, and therefore more acidic, is ocean acidification.
Already this doesn’t sound good, but what is the specific concern about excess carbonic acid in the ocean? Acids, by definition, release hydrogen ions in solution. (An ion is an atom or molecule with a positive or negative electric charge.) Hydrogen ions are very reactive, and in the presence of a carbonate ion (CO-3) two hydrogen ions will bind with it to form a bicarbonate ion. Therein lies the rub: Shell-building marine animals combine relatively unreactive calcium ions in the water with carbonate to form calcium carbonate, the stuff of which their shells are made. However, they can’t liberate carbonate from bicarbonate, and if bicarbonate is all that’s available, they’re out of luck. What’s worse, if carbonate is not available in “free” form for hydrogen ions to bind with, they are reactive enough that they can break existing calcium carbonate apart to “liberate” the carbonate. In effect, sea shells will slowly dissolve in an acidic solution.
Many marine organisms have calcium carbonate shells: mollusks like clams, oysters, scallops, snails, and mussels; crustaceans such as barnacles and crabs; echinoderms including sea urchins and starfish; and even calcareous protozoans like dinoflagellates, cocolithophores, and foraminifera. All these animals are important members of the marine ecosystem, with the protozoans in particular forming part of the oceanic plankton that is the basis of the food web. But perhaps the most concern lies in how ocean acidification may affect coral reefs in the long term. Coral reefs provide shelter for nearly one-quarter of all known marine species, including more than 4,000 species of fish. There are over 1 million species, plants and animals combined, that are associated with reefs in one way or another. Along with rain forests, coral reefs are one of the most biologically diverse ecosystems on Earth. With coral reefs already under threat from a warming ocean, impeding their ability to secrete their vital calcium carbonate shells may be something humanity most regrets in times to come.
Fort Matanzas National Monument is located on the edge of one the world’s most stupendous natural features- the Atlantic Ocean. The Atlantic is the second largest of the Earth’s four oceans, covering about 21% of the globe and containing approximately 22 billion billion gallons of water. Its depth ranges from sea level to 27,841 feet at the Puerto Rico Trench (located north of the eponymously named island). Probably the most distinguishing feature of ocean water is its salinity. Due to the presence of salts and minerals washed into the seas over the eons from terrestrial sources, ocean water has a salinity of 3.5%. This is mostly due to the presence of sodium chloride, but also to minerals like magnesium, sulfate, calcium, potassium, etc. that were once part of rocks which were slowly eroded and carried downstream in rivers to their ultimate destination.
