What are the impacts of ocean acidification, and what steps we can take to mitigate its effects
What Role does the Ocean Play in Global CO2 levels?
We all have a connection to the ocean —even if we do not live along a coastline. It helps each and everyone of us by generating 50% of the oxygen we need. Without the ocean, there would be no food security or economic progress. The ocean helps us mitigate climate change by tempering the rise of atmospheric CO2. Roughly half of the CO2 absorbed by the earth is absorbed by the ocean. Without the oceans helping to remove CO2 from the atmosphere, CO2 levels would have increased even more than they have in the past few decades.
These benefits are often taken for granted and occur at the expense of ocean health. Oceans play an integral role in moderating the rate and severity of climate change; however, by doing so, ocean health is susceptible to adverse impacts.
What is Ocean Acidification?
These impacts are primarily a result of the influx of atmospheric CO2 from human activities such as burning fossil fuels, land-use change, etc. The influx of human-induced atmospheric CO2 is shifting the ocean's chemical balance by decreasing the pH and the availability of minerals and nutrients to marine life. The shift in chemical balance is known as ocean acidification. This happens when CO2 from the air dissolves in the water and reacts with it forming carbonic acid. This increases the acidity of the water, which can be harmful to sea creatures, creating a ripple effect throughout the food web, as organisms that rely on those species for food may also suffer.
H2O + CO2→ H2CO3 (Carbonic Acid)
Since the industrial revolution, the concentration of atmospheric CO2 has increased, causing the pH of surface ocean waters to drop by 0.1 pH units. While this might not sound like much, the pH scale is logarithmic, which means this change represents an approximate 30% increase in acidity. Based on future projections, if we continue with a business-as-usual approach to CO2 emissions, by 2060, seawater acidity could increase by 120%. What will happen to ocean ecosystems? It’s difficult to predict with certainty. We are however seeing the effects already. For example, the oyster industry in the Pacific has lost nearly 110 million USD in annual revenue due to ocean acidification (Ekstromet al., 2015).
What is the Threat?
Ocean acidification can potentially threaten valuable services to society, such as carbon storage, food security, livelihoods, economic well-being, climate regulation, and coastal protection. The climate-regulating capacity of the oceans is not unlimited; as the oceans acidify, their capacity to act as a carbon sink decreases.
When there's too much CO2 in seawater, it can harm organisms that make shells and skeletons out of a substance called CaCO3. These organisms include phytoplankton, zooplankton, corals, clams, and mollusks. When there's too much CO2, it reacts with the naturally occurring carbonate ions to make more bicarbonate ions. This reduces the amount of carbonate available for organisms that need it to make their shells and skeletons. This can disrupt the food web and ultimately harm marine ecosystems.
It’s possible that about 37% of marine species will be negatively affected by ocean acidification alone, not yet considering any co-stressors. For example, the tiny sea snails (also known as "sea butterflies”) that are important to food webs and eaten by a variety of organisms, from juvenile salmon to whales, have been observed to be experiencing malformations, lower rates of CaCO3 precipitation, and severe levels of shell dissolution.
Coral reefs are also highly sensitive to ocean acidification having adverse effects on skeleton formation and causing skeletal dissolution (not coral bleaching, which is actually due to increased temperatures). Another species potentially affected is salmon, whose calcified structures in the inner ear, necessary for sound detection, do not form properly, leading to various behavioural changes and increasing mortality.
These adverse effects could significantly impact food security, fisheries, and aquaculture industries, as seafood is a critical and highly globally traded dietary component. Under current projections using the highest CO2 trajectory for the year 2100, the global and West Arctic ecosystems (which includes the high Canadian Arctic) fisheries catch are forecasted to decline by as much as 3.4% and 20%, respectively. These forecasted declines in fisheries catch will be accompanied by further declines in employment within these industries.
Is there a ‘good’ side to ocean acidification?
Much like climate change, ocean acidification is a globally disruptive problem with many uncertainties regarding the overall impacts and changes to the ocean that will occur as a result; however, there will inevitably be “winners” and “losers” in ocean ecosystems. The “winners” include non-calcifying species such as jellyfish, algae, and seagrasses that potentially favour more acidic conditions that ocean acidification creates.
However, these species alone are unlikely to be able to support the ecosystems that exist in the ocean today that we depend on. Among the “losers” will be parts of the world whose temperatures and circulation patterns (e.g., upwelling) enable the ocean to absorb more atmospheric CO2. These hotspots include the Arctic Ocean and coastal regions.
If ocean acidification is so important, why aren’t more people discussing it?
Unlike global warming, ocean acidification, until recently, has been highly neglected due to being erroneously viewed as a symptom instead of a problem concurrent to climate change —the “evil twin of global warming.” As a result, ocean acidification is largely absent from policy and management discussions about climate change/However, countries such as Ireland refer to ocean acidification and its implications in their national climate change adaptation plans and strategies.
What Can we do?
Any efforts toward climate change mitigation, such as reducing greenhouse gas emissions (specifically CO2), will also benefit the oceans. The more CO2 released into the atmosphere through human activities, the more acidic the ocean will become, compromising the integrity of marine ecosystems. While policy and management about climate change focus on adaptation, the question remaining unanswered is whether oceans can respond to the rates of ocean acidification in a manner that continues to provide the services that support life. Worldwide ocean acidification monitoring efforts are only beginning, making it impossible to predict the cascading impacts of ocean acidification precisely. In essence, we are experimenting, going into uncharted territory. Given the rapid acceleration of ocean acidification, it is imperative that we take action to reduce CO2 emissions and bolster scientific research to inform effective decision-making.
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Contributors
Researchers
Katarina Duke
Mauro Aiello, Ph.D.
Lead Author
Denis Koshelev
Lark Scientific Financial Support
Axel Doerwald
Graphics
Adri Poggetti
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