Newswise — Humanity has a history of hasty changes, often leading to unintended consequences. We've seen this pattern with various innovations such as fossil fuels, AI, plastics, and pesticides. While we tend to innovate without fully considering the consequences, there are instances where we have taken a more thoughtful approach, like in the case of carbon dioxide removal.
With carbon emissions on the rise, many scientists, environmentalists, and policymakers recognize the urgency of directly removing carbon from the atmosphere to prevent catastrophic changes to our environment. One such proposal being evaluated by researchers at UC Santa Barbara involves increasing the ocean's alkalinity to enhance carbon sequestration. By accelerating the geologic processes responsible for removing carbon from the atmosphere, which are otherwise slow but potent, this approach shows promise. The study focused on the impact of this method on two critical plankton groups at the bottom of the marine food chain. The findings, published in Science Advances, indicate that the plankton would thrive under this treatment, offering encouraging results and warranting further exploration of this approach.
Lead author James Gately, a doctoral student at UC Santa Barbara, explains that our increasing CO2 emissions are causing ocean acidification. By introducing alkaline compounds into the ocean, the chemistry of seawater changes, converting CO2 into other carbon compounds such as carbonate and bicarbonate ions. This process enables the ocean to absorb more carbon dioxide while mitigating water acidity, akin to adding an antacid to the ocean.
The foundation of the geologic carbon cycle lies in the process of recycling carbon among the Earth, atmosphere, and ocean over extended periods, typically taking tens to hundreds of thousands of years. However, researchers led by James Gately at UC Santa Barbara are striving to expedite this process through ocean alkalinity enhancement.
The main concern driving Gately and his colleagues is how marine life will respond to large-scale ocean alkalinity enhancement. To address this question, they focused on the impact of this treatment on two crucial plankton groups: diatoms and coccolithophores.
These plankton play a vital role as primary producers, converting sunlight into food and forming the foundation of the ocean's food chain. Professor Débora Iglesias-Rodriguez, Gately's advisor in the Department of Ecology, Evolution, and Marine Biology, emphasizes their significance in the biological carbon pump, a mechanism by which the oceans sequester carbon dioxide from the atmosphere over millions of years. Additionally, these plankton build exoskeletons, transporting substantial amounts of calcium, silica, and carbonate throughout the biosphere.
Annual phytoplankton blooms, including coccolithophores and diatoms, serve as food for small fish and other organisms up the food chain. After the blooms, the dead cells settle on the seafloor, forming carbonate or silica-rich sediment. Over time, this sediment traps carbon from the atmosphere that the organisms absorbed through photosynthesis. Eventually, it can solidify into chert and limestone. Therefore, any negative impacts of ocean alkalinity enhancement on these plankton could have severe consequences.
To investigate the effects of ocean alkalinity enhancement, the research team conducted experiments using water collected from the Santa Barbara Channel. They replicated the natural alkalinity process, where minerals like olivine and various carbonates provide alkalinity over geologic time, by using alternative compounds that dissolve and react more rapidly. After sterilizing the water, they exposed it to air containing approximately 420 parts per million of carbon dioxide, similar to current atmospheric levels. Subsequently, the researchers introduced diatoms and coccolithophores that they had cultured in the laboratory.
The typical alkalinity of the modern ocean ranges from 2,300 to 2,400 micro-moles per kilogram of water. The team conducted two trials, one at 3,000 µmol/kg to simulate long-term alkalinity addition and another at 5,000 µmol/kg to mimic potential hotspots, resembling a treatment site.
Throughout the experiments, the researchers measured various changes in the physiology and biochemistry of the plankton, along with the seawater's chemistry. They were particularly interested in whether the coccolithophores would increase their calcification in response to the treatment, as it would elevate the abundance of calcium ions in the water. Interestingly, the production of calcium carbonate generates CO2, despite containing carbon and oxygen. However, over extended periods, the sequestration effects outweigh this CO2 production, making coccolithophores one of Earth's significant carbon sinks.
Overall, the plankton exhibited a neutral response to the alkalinity treatments, and there was no significant change in calcification. Although the photosynthetic efficiency of the cells decreased slightly, it remained within healthy levels for both treatments. The researchers speculate that this decrease might be attributed to reduced availability of micronutrients, such as iron.
During their research, the team observed that at higher alkalinities, dissolved ions underwent precipitation, transforming into solid compounds. This phenomenon has the potential to deplete nutrients and alkalinity from the solution, which could impact marine life and reduce the effectiveness of ocean alkalinity enhancement. The researchers are already exploring this process through further experiments.
Lead author Iglesias-Rodriguez stated, "When we increased the alkalinity in the water, the physiology of these organisms remained unchanged." Although the initial results are promising, the authors emphasize the need to be cautious about extrapolating these findings to the entire ecosystem, as responses may vary among different species. While studying phytoplankton is a positive step, the team intends to extend their investigations to other organisms and ecosystems.
Presently, the group has embarked on alkalinity enhancement experiments involving entire plankton communities under natural nutrient concentrations. They will assess the responses of individual species as well as the collective community. Ultimately, the team aims to transition their research from the laboratory to real-world field studies. While this prospect is exciting, Iglesias-Rodriguez stresses the importance of proceeding with caution during these endeavors.
Ocean alkalinity enhancement, like many other geoengineering proposals, sparks controversy. James Gately clarified that their research aims to determine the feasibility and potential consequences of this approach rather than endorsing it as a solution.
The urgency arises from the realization that simply reducing emissions is no longer sufficient to limit global warming to within 2 degrees Celsius. To achieve gigaton-scale carbon removal, multiple strategies must be employed, and ocean alkalinity enhancement is just one of them. While Gately acknowledges that none of these technologies alone can single-handedly address climate change, ocean-focused methods hold appeal due to the ocean's capacity to sequester significantly more carbon than the land and atmosphere combined.
However, it is crucial to recognize that geoengineering alone cannot solve the problem unless accompanied by substantial reductions in greenhouse gas emissions. Gately uses the analogy of being in a boat with a hole—trying to scoop out water with a bucket helps, but if the hole remains unplugged, the boat will ultimately sink. In other words, addressing the root cause of the issue, which is reducing emissions, remains paramount.
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