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What is Ocean Acidification and What Risks Does it Pose to Marine Life?

Emily Heaslip

On land, we’re familiar with acid rain — precipitation with acidic components, such as sulfuric or nitric acid. Acid rain can be produced by volcanic events — such as the recent natural disaster in Tonga — as well as by the burning of fossil fuels, manufacturing, and emissions from vehicles and heavy equipment.

What many people don’t realize, however, is that these high-pollution activities also have severe consequences for the world’s seas, primarily via ocean acidification. Ocean acidification is the process by which the pH of the ocean is reduced over an extended period of time. As the ocean’s pH drops, its acidity rises, a phenomenon caused in large part by increases in atmospheric carbon dioxide (CO2).

Today, the acidity of the ocean is greater than it has been at any point in the past two million years. This introduces serious risks for marine life, such as coral bleaching, impeded shell growth, and toxic algae blooms. Let’s unpack how ocean acidification works, how it impacts marine ecosystems, and how we can measure and combat its effects using data. 

What is ocean acidification?

The ocean is a “carbon sink,” meaning it naturally absorbs CO2 from the atmosphere. As CO2 is absorbed, a series of chemical reactions in seawater result in an increased concentration of hydrogen ions which, in turn, cause the pH of the seawater to drop. If the amount of CO2 in the atmosphere increases to dangerous levels, however, so will the amount of CO2 that is absorbed by the ocean, a phenomenon we are currently observing. Over the last century, in response to rising levels of atmospheric CO2, the ocean’s pH has dropped by 26%, i.e. it has become 26% more acidic.

Ocean acidification makes it difficult for marine life, such as coral reefs, to build up the calcium deposits necessary to thrive.
Photo credit:
NOAA

Ocean acidification is getting worse each year. Since the Industrial Revolution, the ocean’s pH has dropped from 8.2 to 8.1, and is anticipated to fall by another 0.3-0.4 pH units by the end of this century. While that may not seem like a lot, remember that the pH scale is logarithmic: this means that pH 4 is ten times more acidic than pH 5 and 100 times more acidic than pH 6.

“If we continue to add carbon dioxide at current rates, seawater pH may drop another 120 percent by the end of this century, to 7.8 or 7.7, creating an ocean more acidic than any seen for the past 20 million years or more,” wrote the Smithsonian Institute.

It’s worth noting that ocean acidification doesn’t impact each part of the ocean evenly. Ocean currents and circulation transfer CO2 vertically as well as to different areas of the ocean. In the polar regions, for instance, cold temperatures facilitate atmospheric CO2 dissolution, with the dense water at these higher latitudes dragging down dissolved carbon and storing CO2 more effectively. Climate change, however, is complicating this dynamic, as polar ice caps melt and ocean circulation slows.

[Read more: Understanding Surface Currents vs Deep Ocean Currents]

Impacts of ocean acidification on marine life 

We’ve already seen plenty of evidence that ocean acidification is decimating marine ecosystems. It has had a major impact on both shellfish and coral reefs, each of which needs carbonate ions to make their shells and skeletons. Acidification reduces the availability of carbonate ions, preventing these populations from thriving and disrupting delicate ocean ecosystems. Scientists estimate that over the next 20 years, 70% - 90% of reefs will disappear, with rising sea temperatures — which are also linked to increases in atmospheric C02 levels —  causing corals to lose their algae and bleach. Additionally, ocean acidification makes it difficult for individual corals to build up the calcium deposits necessary to produce larger reef structures.

Phytoplankton and zooplankton
, the tiny plants and animals that form the base of the marine food web, are similarly affected by ocean acidification. These floating creatures become unable to build and maintain their shells, jeopardizing the livelihood of an essential food source for fish, crustaceans, and other larger species.

Ocean acidification and warming ocean temperatures are bad for fisheries, too. Consider the shellfish industry. Warmer oceans lead to toxic algal blooms, which, “produce domoic acid, a dangerous neurotoxin, that builds up in the bodies of shellfish, posing a risk to human health,” wrote the Union of Concerned Scientists. To make matters worse, increasingly acidified waters are devoid of the minerals that shellfish need to grow, another blow for fisheries, many of which have been forced to shut down on the West Coast.

Collecting ocean acidification data

Researchers are working to collect better, more complete ocean acidification data through projects like the one led by Aqualink and Sofar. Thanks to this partnership, research teams can take advantage of the world’s largest real-time ocean data platform to view the recorded water temperature and other data at a global network of coral reefs, an ecosystem that is in the midst of a global crisis. By aggregating this data, researchers are able to pinpoint with greater accuracy where ocean acidification and climate change are taking their toll.

Other new, innovative solutions are being proposed to lessen ocean acidification’s negative impacts. For instance, researchers have found that marine vegetation can help effectively absorb CO2 and reduce acidity in the ocean. Studies in the Florida Keys, Indo-Pacific, Oregon, and Maine have all shown the usefulness of seagrasses, eelgrasses, shell beds, etc. in counteracting ocean acidification; in fact, one project in the Indo-Pacific showed that seagrass meadows should give corals about an 18% boost in growth!

Seagrass, however, is challenging to restore, which is why scientists are also examining the usefulness of other marine plants, such as kelp. Kelp forests could provide the dual benefit of removing and storing carbon from the atmosphere and then, once harvested, serving as a source of income for farmers and food for consumers. Kelp, encouragingly, is already a major ingredient in Asian cuisine.

Understanding the impact of these solutions requires timely, accurate ocean data collection. A unified knowledge base will lead to better strategy and planning in our effort to slow down the rate of ocean acidification. This process starts with more affordable and accessible data collection tools, the driving force behind the development of Sofar’s Spotter & Smart Mooring devices.

To learn more about ocean acidification, check out our blog.

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