Acid Oceans? & Oyster Shells

What’s Natural?

Guest post by Jim Steele

Published July 14, 2020 in the Pacifica Tribune

(I wrote a white paper for the CO₂  Coalition, providing more details and references to peer reviewed science regards how marine life counteracts ocean acidification. That paper can be downloaded here )

Search the internet for “acid oceans” and you’ll find millions of articles suggesting the oceans are becoming more corrosive due the burning of fossil fuels, and “acid oceans” are threatening marine life. Although climate modelers constantly claim the oceans’ surface pH has dropped since the 1800s, that change was never measured, as the concept of pH was not created until the early 1900s by beer-makers.

In 2003 Stanford’s Dr. Ken Caldeira coined the term “ocean acidification” to generate public concern about increasing CO₂  . As New Yorker journalist Elizabeth Kolbert reported, “Caldeira told me that he had chosen the term ‘ocean acidification’ quite deliberately for its shock value. Seawater is naturally alkaline, with a pH ranging from 7.8 to 8.5—a pH of 7 is neutral—which means that, for now, at least, the oceans are still a long way from actually turning acidic.” Nonetheless Caldeira’s term “ocean acidification” evoked such undue fears and misunderstandings, we are constantly bombarded with catastrophic media hype and misdiagnosed causes of natural change.

For example, for nearly a decade the media has hyped the 2006-2008 die-off of larval oysters in hatcheries along Washington and Oregon. They called it a crisis caused by rising atmospheric CO₂  and the only solution was to stop burning fossil fuels. But it was an understanding of natural pH changes that provided the correct solutions. Subsurface waters at a few hundred meters depth naturally contain greater concentrations CO₂  and nutrients and a lower pH than surface waters. Changes in the winds and currents periodically bring those waters to the surface in a process called upwelling. Upwelling promotes a burst of life but also lowers the surface water pH.  Not fully aware of all the CO₂  dynamics, the hatcheries had made 3 mistakes.

First, they failed to recognize not all oyster species are well adapted to the low pH of upwelled water. The larvae of native Olympia oysters naturally survive intense upwelling events along the Washington coast because that species “broods” its larvae. The larvae initiate their shells protected inside their parents’ shells where pH is more controlled. However, the Olympia oysters were over-harvested into near extinction in the 1800’s.

So, fishermen imported the Japanese oyster, which is now the mainstay of the Washington and Oregon fisheries. Japanese oysters did not evolve within an intense upwelling environment similar to Washington’s coast. Each Japanese oyster simply releases over 50 million eggs into the water expecting their larvae to survive any mild changes in pH during initial shell formation. Hatcheries didn’t realize the Japanese oyster’s larvae had a 6-hour window during which the larvae’s initial shell development and survival was vulnerable to low pH.

Second, because cooler waters inhibit premature spawning, hatcheries pumped cool water from the estuary in the early morning. As measured in coral reefs, photosynthesis raises pH during the day, but nighttime respiration drops pH significantly. By pumping early morning water into their tanks, they imported estuary water at its lowest daily pH. Finally, they failed to recognize natural upwelling events transport deeper waters with naturally low pH into the estuary, further lowering the pH of water pumped into their tanks.

Now, hatcheries simply pump water from the estuary later in the day after photosynthesis has raised pH. Scientists also developed a metering device that detects intrusions of low pH waters, so hatcheries avoid pumping water during upwelling events. As for most shellfish, once the shell is initiated, a protective layer prevents any shell corrosion from low pH conditions. Problem easily solved and crisis averted!

The simplistic idea that burning fossil fuels is causing the surface ocean to become more acidic is based on the fact that when CO₂  interacts with water a series of chemical changes results in the production of more hydrogen ions which lowers pH. Unfortunately, all catastrophic analyses stop there. But living organisms then reverse those reactions. Whether CO₂  enters the surface waters via the atmosphere or from upwelling, it is quickly utilized by photosynthesizing plankton which counteracts any “acidification”. A percentage of the organic matter created in the sunlit waters sinks or is actively transported to depths, further counteracting any surface “acidification’. Some organic matter sinks so rapidly, CO₂  is trapped at depths for hundreds and thousands of years. The dynamics that carry carbon to ocean depths largely explains why the oceans hold 50 times more CO₂  than the atmosphere.

To maintain marine food webs, it is essential that upwelling bring sunken nutrients back into the sunlight to enable photosynthesis. Upwelling also brings stored CO₂  and low pH water to the surface. Wherever upwelling recycles nutrients and lowers surface pH, the greatest abundance and diversity of marine life is generated.

Jim Steele is director emeritus of the Sierra Nevada Field Campus, SFSU and authored Landscapes and Cycles: An Environmentalist’s Journey to Climate Skepticism.