Increased levels of carbon dioxide in the oceans result in marine water acidification, which has tragic impacts on marine ecosystems and biota. Two recent articles published in the EOS caught my attention as they discuss solutions (with pros and cons) for dealing with oceanic carbon dioxide.
Context: Many oceanographers have been reluctant to conduct mCDR research because:
Removal of marine carbon dioxide may encourage more emissions of carbon dioxide into the atmosphere
It could distract ocean scientists from other research activities
However, some ocean scientists feel the urgent need to conduct mCDR research because of global warming’s potential adverse impacts, from wildfires and desertification to increased hurricanes.
MCDR methods include:
Ocean iron fertilization, artificial upwelling of nutrients, and seaweed cultivation to stimulate plankton productivity on the ocean’s surface
Ocean alkalinity enhancement by spreading lime on the ocean’s surface to increase marine carbon dioxide uptake
Direct removal of carbon dioxide from sea water
Each method has its own challenges, scopes, and demerits. All need to be evaluated and documented.
Monitoring, Reporting, and Verification (MRV): The amount of carbon dioxide removed by a CDR project conducted over a given period is monitored and reported to a third party, who then verifies the results and reports to stakeholders.
Building a common ground: The article mentions a newfound and notable enthusiasm around removing carbon dioxide in oceans witnessed at a September 2022 workshop sponsored by Ocean Carbon & Biogeochemistry Project Office with support from the U.S. National Science Foundation and NASA and held at the University of Rhode Island.
The OCB meeting highlighted common ground for MRV among ocean scientists:
Any MRV framework depends on a particular mCDR method applied; therefore, several MRV guidelines and baselines need to be developed.
MRVs are multidisciplinary and international efforts and require contributions from geoscientists and biologists from around the globe.
MRV data should be transparent, science-based, and publicly available.
MRVs require adequate funding from U.S. government agencies such as the National Science Foundation, Department of Energy, and the National Oceanographic Partnership Program of NOAA.
What’s next: The 2025 OCB workshop will be held on June 3–6 at the NASA Ames Conference Center (Moffett Field, California).
Another group of scientists have suggested a new method to withdraw carbon dioxide from marine waters by using ocean-floor transform faults. Their article was also recently published in EOS.
Transform zones:
Transform faults connect divergent plate boundaries at mid-ocean ridges and are parts of the structures responsible for ocean floor spreading.
Discovery of transform faults in the 1960s was key in the development of plate tectonic theory.
Transform zones are strike-slip faults with adjacent submarine valleys that expose segments of the oceanic crust sliding off the underlying mantle.
What they’re saying:
The scientists suggest drilling into and fracturing submarine valleys adjacent to transform faults.
Enhanced fractures will circulate more seawater into the underlying mafic rocks, such as peridotite.
The infiltrated waters will become more alkaline (pH 10), which will then rise and react with dissolved carbon dioxide in seawater to form precipitate calcite (CaCO3).
Natural analogs: The suggestion is analogous to hydrothermal vents on the ocean floor that have already been in place for billions of years.
The transform faults host low-temperature hydrothermal systems, which withdraw dissolved carbon dioxide by precipitating calcite.
A notable example is the Lost City hydrothermal field located at about 30 N latitude, 15 kilometers west of the Mid-Atlantic Ridge. It was discovered in 2000. The carbonate towers and hydrothermal chimneys of the Lost City resemble a fantastic city—hence the name.
The high pH fluids circulated from the vent originate from the hydration and serpentinization of olivine and similar iron-magnesium rich minerals beneath the seafloor.
Pros and cons:
Earth’s mantle constitutes over 80 percent of Earth’s volume and is made up of ultramafic rocks with low silica and high iron-magnesium elements.
It is estimated that merely 600 cubic kilometers of mantle rock could withdraw all the atmospheric carbon dioxide emitted from burning fossil fuels over the past two centuries.
Like many other large-scale geoengineering proposals, the new suggestion faces technological, financial, and environmental challenges.
For instance, fracturing enhancement of the ocean floor may disturb deep marine habitats and even release large volumes of methane, a stronger greenhouse gas than carbon dioxide.
The method will require detailed, multifaceted assessment.
Thank you to all who submitted answers to last week’s quiz question.
As a reminder, the question was: Obsidian, or volcanic glass, usually has a dark color, often black. Is it a mafic or felsic rock? Briefly explain.
Revathy Venkatesan, Ramiro Bracamonte, and Pete Webb correctly responded to last week’s quiz. Here are some key takeaways:
Despite its dark color (which is usually a mark of mafic minerals and rocks), obsidian is formed by rapid cooling and solidification of felsic magma rich in silica (65–70 percent). It is often black because of a small content (less than 2 percent) of iron and magnesium, which is present in the form of sub-microscopic mineral particles such as magnetite, biotite, and amphibole.
Let’s look at the question for this week’s quiz: What are the top three deepest canyons (gorges) in the world? Please list name, location, and depth. (Hint: The Grand Canyon is not one of them).
Send your response by October 17 to editorial@aapg.org (subject line: Core Elements Quiz)
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