Earth’s Oceans are vast and beautiful worlds that cover 71% of our planet, but their inner workings still remain very much a mystery; an estimated 95% of the Ocean is still left to be explored. Its greatest depths and countless “webs” and symbiotic relationships between species, remain some of the most exciting frontiers of scientific research today.
Regardless of how much remains to be discovered, the Ocean is a Vital Common Resource for human beings, shared by all, much as the atmosphere is (Alexander Von Humboldt eloquently referred to the Atmosphere as “The Air Ocean”). Many scientists, anthropologists and historians are in agreement that if it were not for the relative stability of the Oceans over the past several thousand years, human civilization would have never taken hold and flourished. In parallel with primitive terrestrial agricultural systems, the Ocean’s bountiful stock of nutritious protein, along with unusually stable sea levels (paleoclimatic data shows that through Earth’s history there has very rarely been an extended time of such minimal sea level change), likely allowed civilizations and cultures to be founded and to grow formidable in MesoAmerica, Africa, Asia, Mesopotamia, and more, all around the same time period 5-7,000 years ago. Even now, 50% of people live within 30 miles of the coast, and one in seven people still depend on the ocean as their primary source of protein.
As is the case with much of the Earth’s landmass, human beings have managed to permanently transform the Oceans, from its complex ecosystems and rich biodiversity, to its actual chemistry! What once seemed like a limitless and unalterable fixture of this planet, the Ocean is now in a battle to adapt itself to the ever increasing influences of our species.
The world’s Oceans are vast carbon sinks, helping to absorb excess carbon dioxide in the atmosphere and limiting the impact of atmospheric global warming caused by fossil fuel emissions. Along with carbon captured from forests, other vegetation, and freshwater sources on land, approximately 50% of the carbon dioxide released into the atmosphere in the last 200 years since the Industrial revolution (where carbon dioxide has increased from around 180 parts per million to over 400 parts per million) has been absorbed. While this “buffer” has benefits in mitigating the effects of Climate Change, what’s being felt below the surface is far from beneficial.
This absorption of carbon dioxide from the atmosphere leads to the acidification of the ocean, which has widespread consequences. Paired with other climatic changes, such as rising ocean temperatures, rising sea levels and stronger storms, many of the Oceans ecosystems and food webs are at tremendous risk. This in turn poses a major risk to the health and food security of a large portion of the world’s poor, and also has far reaching consequences for the diets and economies of developed nations. Ocean Acidification, as it is referred to, results from the chemical reaction of Carbon Dioxide (C02) absorbed from the atmosphere, and water (H20). They combine to form Carbonic Acid (H2CO3), which itself rapidly releases a Hydrogen Ion, or Proton (H+), leaving a Bicarbonate Ion (HCO3-). Bicarbonate Ions also often lose a proton (H+) to become Carbonate (CO3 2-), which is a naturally occurring and essential building block in the Ocean. Acidity is defined by the pH scale (0-14), which measures the concentration of protons in any given substance.
Projecting an Acidic Future
Through the reactions described above, the Oceans are building up more free protons and becoming more acidic (lower pH). Since the start of the Industrial revolution at the end of the 19th century, pH levels of the Ocean have dropped from approximately 8.2 to 8.1. While 0.1 doesn’t seem like a lot, because pH is a logarithmic scale, this actually translates to an approximately 30% increase in acidity of the Oceans. By 2100, based on carbon dioxide emissions projections and estimated Ocean absorption capacity for carbon dioxide, it is estimated that the pH of the Oceans will drop by another 0.2 to 0.5 in pH. This will have wide ranging consequences, including the dissolution of certain calcifying organisms that are essential to the survival of marine ecosystems.
This isn’t the end of the story though, and the responses that the Ocean and its species are having to increasingly excessive absorption of carbon dioxide and acidification are only beginning to be understood. One clear response, however, is an attempt by the Ocean to get back to a sort of equilibrium by reversing the last part of the above process, recombining Carbonate Ions (CO3 2-) with a proton (H+). This consumption of Carbonate Ions has profound repercussions for marine species. Specifically, the removal of Carbonate from the ocean to help balance the rising acidity leaves less Carbonate available to combine with naturally occurring dissolved Calcium (Ca 2+) in the Ocean to form Calcium Carbonate (CaCO3) (Scientists describe this as the lowering of the “saturation state” of carbonate in seawater). Calcium Carbonate, in its two most notable forms Aragonite and Calcite, are the building blocks for calcifying organisms, from Coral that need it to build their skeletons, to Molluscs and Crustaceans who need it to build their shells. It is important to mention that Aragonite has a saturation state at a much higher ocean depth than Calcite, and is much more susceptible to Ocean Acidification, so those species who form their shells and skeletons with Aragonite, such as Coral, most Mollusks and Pteropods, are much more at risk.
To state it more directly, excess Carbon Dioxide in the atmosphere leads to Ocean Acidification, and Ocean Acidification both lowers the pH of the Oceans and decreases the availability of fundamental building blocks for marine ecosystems like coral reefs and also for shellfish. Marine life had already been stressed to the limit in many areas due to overfishing and runoff from land-based pollution. Runoff of fertilizers, herbicides, pesticides and animal waste from Industrial farms, including aquacultures, actually cause localized increases in the acidity of coastal Ocean waters in a process called eutrophication, which also can lead to the deoxygenation of large areas of Ocean that are then termed “dead zones,” as little to no life can live there.
Many coastal waters also go through cycles known as “upwelling,” where deep Ocean water richer in carbon (from sedimentation of phytoplankton and other organic compounds especially) is cycled up to the surface and surface water is pushed down to the depths, increasing the acidity of surface waters periodically. How localized pollution and natural upcycling interact with global ocean acidification and in turn exacerbate the overall problem for ecosystems, needs to be better understood, but coastal waters, where many Coral reefs and commercial fisheries exist, are particularly susceptible to the problems of Ocean Acidification. Coral reefs in particular also suffer from other effects of Climate Change. From rising Ocean temperatures that cause “thermal stress” and is the primary cause of “coral bleaching” and the spread of infectious diseases in Coral, to stronger storms that cause direct destruction to corals, and sea level rise, which increases sedimentation and can suffocate coral. According to a report published by OCEANA about Ocean based food security around the world, “About a quarter of all marine fish species live on coral reefs and about 30 million people around the world depend on these fish as an important source of protein.”
The relationship between Ocean Acidification and the rising temperatures of Oceans is also only beginning to be fully understood. It is known that colder waters absorb more Carbon Dioxide, meaning the polar regions are the first to go through major alterations of Ocean chemistry due to carbon dioxide absorption and acidification. But ocean temperatures are rising due to climate change, and those rising temperatures are also most pronounced in polar regions, so because of this there is less ability for the Ocean to absorb carbon dioxide. While rising Ocean temperatures are a potentially positive thing in terms of mitigating Ocean Acidification, the limited ability of the Ocean to absorb carbon dioxide means more carbon dioxide will stay in the atmosphere, causing more atmospheric warming, higher ocean temperatures still, and even less ability to absorb carbon dioxide. This is called a positive feedback loop in regards to climate change and rising temperatures, though it may save the Oceans from an exponentially increasing level of acidification.
In addition, rising Ocean temperatures are already forcing the migration of many tropical fish populations that can only live within a certain temperature range, towards the poles (or to deeper depths), where they will then experience more acidic waters and new forms of biological stress. These migrations are also putting poor tropical fishing communities at risk of losing their principal sources of protein.
The influence of Ocean Acidification is already being felt in fundamental marine ecosystems like Coral Reefs, and directly on mollusk and other shellfish populations, as well as on several fundamental species for marine ecosystems such as pteropods and some plankton that form the bases of many complex food webs. Pteropods, for example, which are tiny sea snails often referred to as “sea butterflies,” form the base of food webs in the Arctic. They are extremely susceptible to both dissolution of their aragonite-based shells in acidic waters and are unable to grow or regrow their shells due to lowered carbonate saturation states. They are essential in the food chain of commercially important fish such as Salmon, Mackerel, Cod and Herring, whose populations are greatly at risk now if pteropods continue to die off because of increasing acidification of the Oceans. Mollusks such as Oysters and Clams have shells made of aragonite, and have populations already directly suffering as a consequence of Ocean Acidification. Mollusks are important food sources both for humans (especially in certain developing tropical nations like Aruba) and certain large commercially important fish like Halibut, Flounder and again Herring and Cod. The higher acidity of the ocean is also likely to have direct impacts on many marine species in ways outside of shell formation and food sources.
From interfering with echolocation in various animals such as whales (because changing pH of the Oceans will change the acoustic properties of the Ocean), to altering reproductive and metabolic function in many species, the consequences could be far-reaching. To this point, however, these areas of research are very young and inconclusive as it is not known how quickly each individual species can adapt to these changes in the Ocean’s chemistry.
However, It has been documented by researchers that the current rate of acidification of the Ocean is faster than any time in the past 300 million years of earth’s history, and around 10 times faster than the latest Mass Extinction event (The Paleocene-Eocene extinction event around 55 million years ago). This means that the changes may be far faster than the species’ are able to adapt to. More awareness, attention and funding needs to be given to these phenomena to form a better understanding of the impact our species is having on the Ocean. One thing is certain, however; when it comes to halting Ocean Acidification, there is no quick fix. Oceans take thousands of years to adjust to chemical perturbations and temperature changes, and the most innovative and ambitious geoengineering proposals to address climate change do little to alleviate Ocean Acidification (one example, capturing carbon dioxide from the atmosphere and pumping it into the depths of the Ocean for sequestration, would likely only make the deep Ocean more acidic).
Other proposals, like increasing phytoplankton populations and photosynthesis by adding iron to the Oceans will likely also just acidify the deep Ocean more as the phytoplankton sinks to the sea floor. Carbon Dioxide emissions are the direct cause of Ocean Acidification, and there must be an effective and escalating policy in reducing their emissions if we are to protect this Vital Common Resource from unalterable and potentially catastrophic changes.
Resources and Further Reading
Chomo, Victoria. De Young, Cassandra. “Towards sustainable fish food and trade in the face of climate change.” International Centre for Trade and Sustainable Development (ICTSD). March 2015.
Chu, Jennifer. “Ocean acidification may cause dramatic changes to phytoplankton.” MIT News Office based on study in Nature Climate Change. July 2015.
Doney, Scott. Fabry, Victoria. Feely, Richard, et al…”Ocean Acidification: The Other CO2 Problem.” Washington Journal of Environmental Law and Policy. 2009.
Fabry, Victoria. Feely, Richard. Orr, James. Seibel, Brad. “Impacts of ocean acidification on marine fauna and ecosystem processes.” ICES Journal of Marine Science. April 2008.
Feely, R. Bednarsek, N. et al…”Limacina helicina shell dissolution as an indicator of declining habitat suitability owing to ocean acidification in the California Current Ecosystem.” Proceedings of the Royal Society B. June 2014.
Greger, Michael. “Why Would Eating Fish Increase Diabetes Risk?” July 2015.
“How does Climate Change affect coral reefs?” NOAA.
“How Much of the Ocean Have We Explored” NOAA.
Huelsenback, Matthew. “Ocean-Based Food Security Threatened in a High CO2 World: A Ranking of Nations’ Vulnerability to Climate Change and Ocean Acidification.” OCEANA. September 2012.
Humphreys, Matthew. “Climate sensitivity and the rate of ocean acidification: future impacts, and implications for experimental design.” ICES Journal of Marine Science. May 2017.
“Ocean Acidification: How CO2 Emissions and False Solutions Threaten Our Oceans.” Food and Water Watch. June 2015.
Parry, Jane. “Pacific islanders pay heavy price for abandoning traditional diet.” World Health Organization. July 2010.
Spalding, Mark. “Ocean Acidification, Seafood and Food Security.” The Ocean Foundation and SeaWeb. Presentation at February 2016 Seafood Summit.
Valdez, A. Menni, C. et al…”Omega-3 fatty acids correlate with gut microbiome diversity and production of N-carbamylglutamate in middle aged and elderly women.” Nature: Scientific Reports. August 2017.
