Poking the angry beast: The other carbon problem
by Jess Spear
“Pollution of the air or of the land all ultimately ends up in the sea.” - Jacques Cousteau
Article originally published in Issue 3 of Rupture, Ireland’s eco-socialist quarterly, buy the print issue:
When I lived in Florida one of my favourite things to do was to walk along the beach and search for shells. The beaches on the west coast of Florida are bejewelled with giant cockles, slipper shells, lightning whelks, sunray venuses, pen shells, and tiny coquinas in all different colours. There’s even one called a turkey wing that looks just like a turkey wing. While there are considerably fewer shells on the beaches in Ireland, still you find cockles, scallops, and massive razor clams that crunch nicely when you walk on them.
Shells are the skeletal remains of animals that were once eeking out a living (usually in shallow ocean habitats). Some, like the itty bitty coquina, bury themselves in the sand with only a sticky siphon poking out to catch all the microscopic plants and animals in the water. Others, like the lightning whelk, are active predators that use the thin edge of their shell to pry open other shells and eat the animal’s soft parts. And just like the bones in our bodies, these shells are composed of calcium carbonate (CaCO3).[1] When you comb the beach for shells, you’re looking for and collecting the (beautiful) “bones” of these dead animals.
Corals too build a hard exterior. Tropical reef-building corals live in colonies with millions of individual, but genetically identical, polyps building a common home. These homes, built bit by bit, polyp by polyp over hundreds to thousands of years, are sometimes large enough to be visible from space. Coral reefs are home to over 4,000 different fish species and support thousands of other species including sea turtles, birds, and sea mammals. Shallow water corals, of which most of us are familiar, are vibrantly coloured from the algal symbionts living within[2] helping to nourish the coral. Less well known are the deep-sea, cold-water corals. These slow growers, living in mostly dark frigid waters, are also important habitat builders.
Crushed and eroded by waves, the skeletal remains of these organisms become part of the sand. Over millions of years of accumulation, they form limestone much like the Burren limestone formed over 300 million years when Ireland was located near the Equator and covered in a shallow sea. South Florida is entirely constructed of shells of one type or another.
In addition to the corals and clams are all kinds of microscopic animals and plants (or plankton) that also excrete a carbonate exoskeleton. We don’t normally see them because they’re so tiny and because most of their shells end up buried in the deep ocean. However, they can bloom in huge numbers, making trillions of microscopic individuals visible from space, and in some areas their shells wash ashore, making up the bulk of sand on some beaches. Japan has a beach almost entirely constructed of star-shaped Foraminifera shells and Bermuda’s pink sands are coloured by a species of Foraminifera that builds a pinkish-red shell. The famous White Cliffs of Dover are made from the carbonate plates of the coccolithophores, a microscopic algae. Nonetheless, these tiniest of shells play a massive role in marine ecosystems as a key source of food for other animals, as well as in the carbon cycle, helping draw down carbon from the atmosphere and store it in ocean sediments and rocks.[3] In fact, the oceans are the largest “sink” of carbon on the planet.
But the ability of these organisms to build their shells, to eat, respire, reproduce, and add to the complexity of the marine ecosystems in which they live, is under threat. The fossil carbon, dug up and burned over the last 200 years, has not only polluted the air and trapped more heat. It has also dissolved into the ocean, setting off a chain of chemical reactions that have rendered the ocean more acidic.
Not just salt and water
Like climate, the ocean isn’t and has never been static and unchanging. Over millions of years, ocean basins and continents change shape, expand and contract as they glide around on plates atop the mantle of the earth. They collide to form supercontinents and mountain chains and then break apart as new ocean basins are born and others melt back into the earth. The Atlantic Ocean basin is getting bigger. As the seafloor spreads, magma from inside the earth’s mantle rises to the top and cools, forming a chain of oceanic mountains, the Mid-Atlantic Ridge. Meanwhile, the Pacific Ocean basin is shrinking as the Pacific plate is plunging beneath the Philippine sea plate.
As ocean basins grew or shrunk, minerals carried by rivers to the sea and atmospheric gases (such as CO2) dissolving into and out of the ocean over time have modified the ocean’s chemistry. In addition to the salt we can taste (a molecule made of two elements, sodium and chloride, NaCl), ocean water has many other elements and ions (a negatively or positively charged molecule) dissolved in it, such as magnesium, calcium, boron, potassium, and carbonate to name only a few. These minerals are vital to life in the ocean. From the microscopic zooplankton and phytoplankton that feed tiny fish babies to the largest animal to ever inhabit the earth, the blue whale, marine life has evolved to live in the ocean over millions of years, adapting to relatively slow-changing ocean conditions. Upsetting the chemical balance, like pulling on one tiny strand in the ocean web of life, will have disastrous and far-reaching effects.
Chain reaction
Approximately 22 million tons of CO2 dissolve into the ocean every day. This adds to the roughly 525 billion tons of CO2 the ocean has already absorbed since the start of the Industrial Revolution 250 years ago, 30% of all emissions. This additional carbon substantially alters the chemistry of the ocean, making it more acidic (see box).
All those animals constructing such beautiful shells, shells that we spend hours walking up and down the beach searching for, are now under threat. They won’t be immediately dissolving or anything like the bicarbonate and vinegar reactions we’ve seen (see box: Ocean Acidification) - though in some experiments where researchers created ocean pH conditions projected for 2100, some sea butterfly (pteropod) shells dissolved after 45 days. However, they depend on the ocean having adequate calcium and carbonate available. Like us, they draw what they need to build themselves not only from what they eat but also from the water they live within.[4] We consume all kinds of minerals needed to make and repair our bones, muscles, skin, and organs, but we also breathe in and use the oxygen from the air we move through. Ocean acidification makes it much harder for them to live. It would be like forcibly moving you to the top of Mount Everest where there is roughly 30% less oxygen than at sea level.
Ocean Acidification
When CO2 combines with water it makes carbonic acid and releases a hydrogen atom. How much free hydrogen a solution has determines its pH level. You might recall from chemistry class that pH tells you whether a solution is acidic or basic and the lower the pH, the more acidic, the higher, the more basic (or alkaline). Freshwater from the tap usually has a pH of around 7, which is neutral on the pH scale. Common acids like lemon juice have a pH of about 2, just slightly less acidic than our stomach acid and battery acids. On the other side of the scale are the basic (or alkaline) solutions such as bicarbonate of soda, ammonia, and household bleach.
Acids and bases react with one another - sure we’ve all seen the “volcanoes” made with vinegar and bicarbonate of soda or coca-cola and mentos. The coca-cola has carbonic acid in it, all those bubbles are CO2!
The more CO2 that enters the ocean, the more acidic it becomes. The free hydrogen released when CO2 combines with water then goes on to react with the carbonate molecules needed to make and repair shells as the organism grows.
The ocean wouldn’t be classified as an acid on the pH scale, though. Because of all the minerals in it, seawater has a pH above 7 and is technically basic. Nonetheless, the CO2 dissolved into the ocean has decreased the pH from 8.2 to 8.1.
This might seem small, but the pH scale is logarithmic, which means a very large range of change is compacted into a small scale. So each unit of change is much bigger than the number suggests. A common example of a logarithmic scale is the Richter scale used to measure the severity of earthquakes. A 6.0 earthquake is equivalent to 60 million tons of TNT exploding, whereas the next unit, 7.0, represents 20 billion tons of TNT exploding. The decrease of just 0.1 in pH represents a 30% increase in acidity!
Canary in the coal mine
Pteropod showing effects of ocean acidification. Image courtesy of NOAA Fisheries Collection.
The only way to stop the acidification is to stop burning fossil fuels. If carbon emissions continue unabated, model projections indicate the ocean’s acidity will increase at a rate that scientists have called ‘unprecedented’ in the last 300 million years.[5] Changes in pH by 2080 could cause some areas of the ocean, particularly in the upper surface waters, to ‘experience year-round corrosive conditions...by 2081–2100’. But, as with climate change above the water, we can see the horrifying impact now.
Present-day Foraminifera shells are nearly 80% thinner than compared to shells recovered around 140 years ago.[6] Scientists discovered a 14% decrease in coral reef construction in the Great Barrier Reef since 1990.[7] Some of the most vulnerable to ocean acidification are the barnacles and limpets and other organisms living in shallow intertidal rocky areas that are periodically submerged at high tide and exposed at low tide. Oyster die-offs have been reported in hatcheries in Oregon and Washington state due to the extremely corrosive waters upwelling and bathing the oyster reefs.
But the canary in the coal mine for the scariest effects of ocean acidification is the beautiful sea butterfly or pteropod. Pteropod shells are made of a more dissoluble form of calcium carbonate called aragonite (as are corals, clams, and many of the shells you find on the beach). In the Canadian Beaufort Sea, just north of Alaska and Canada, scientists recently discovered ‘hotspots of corrosive water’ where up to 70% of the pteropods’ shells were dissolving.
Fisheries are predicted to take a big hit because shelled animals are an important food source for many species of fish. A decrease in fish stock would jeopardize food security for the three billion people that rely on fish for protein, in addition to the consequences on jobs and living standards in communities that rely on recreational fishing and tourism.
The change in acidity will also affect a host of other biological processes of which we are only now getting a grasp. For example, one study found that young clownfish (pictured right) living in water with a pH predicted for 2050 and 2100 didn’t respond to noises - meaning their hearing was impacted. Another found that the clownfish’s smell was impaired and they became attracted to predators rather than repelled. Compared to global warming, research on ocean acidification is relatively new (approximately 20 years old), with most studies occurring since 2004; that and the fact that we cannot observe the effects means most people are unaware of the drastic changes occurring and their far-reaching implications.
Keep in mind that ocean acidification is not the only stressor to marine life. It’s already coping with marine heatwaves, reduced oxygen levels, overfishing, bottom trawling (scraping the seafloor), fertiliser runoff and plastic pollution. This is yet another disastrous effect of capitalism’s production for profit which deems nature both as a free gift to extract raw materials from at any cost and its dumping ground for toxic waste and pollution; and one more reason to fight for ecosocialist change. As the oceanographer Sylvia Earle said, “[w]e need to respect our oceans and take care of them as if our lives depended on it. Because they do.”
Jess Spear was research scientist at the U.S. Geological Survey, St. Petersburg Coastal & Marine Science Center, and then micopaleontologist at the Burke Museum of Natural History at the University of Washington. You can follow her at @jdubspear
Notes
1. Not all shells are made of carbonate - some are made of silica or glass, like Radiolarians.
2. Bleaching is when the coral expels the symbionts, turning the once colourful reefs white.
3. The limestone used to construct the Great Pyramids in Egypt are made from the shells of a now extinct Foraminifera!
4. Scientists have detected fossil carbon in the skeletons of corals and sponges and found that it tracks changes in pH. This is called the ‘Suess effect’.
5. Orr, J. C. et al. Anthropogenic ocean acidification over the twenty-first century and its impact on calcifying organisms. Nature 437, 681–686 (2005).
6. Fox, L., Stukins, S., Hill, T. et al. Quantifying the Effect of Anthropogenic Climate Change on Calcifying Plankton. Sci Rep 10, 1620 (2020).
7. De’ath, G., Lough, J. M. & Fabricius, K. E. Declining coral calcification on the Great Barrier Reef. Science 323, 116–119 (2009).