Important Groups of Phytoplankton Bear Some Strategies for Removing Carbon Dioxide from the Ocean - ScienceDaily -

Important Groups of Phytoplankton Bear Some Strategies for Removing Carbon Dioxide from the Ocean – ScienceDaily

Humanity has a long record of making big changes with little thought. From fossil fuels to artificial intelligence, plastics to pesticides, we love inventing our own problems out of the box, only to find that we’ve created different ones. So it can be refreshing to hear about cases where we’ve taken a step back to trading before committing to a radical new idea, such as removing carbon dioxide.

As carbon emissions continue to rise, many scientists, environmentalists and policy makers have called for action to remove carbon directly from the atmosphere. They argue that such geoengineering approaches are necessary to avoid catastrophic changes to our land, atmosphere and sea.

Researchers at the University of California, Santa Barbara, are evaluating the effects of one such proposal, which includes increasing ocean alkalinity to enhance carbon sequestration. The goal is to speed up the geological processes that remove carbon from the atmosphere, which are very powerful but very slow. The team investigated how this affected two of the most important groups of plankton in the ocean at the bottom of the food chain. Their findings, published in Science advancesindicate that plankton will fare well under the treatment, a positive finding that encourages further investigation of this promising proposal.

We also add CO2 “Adding an alkaline is basically like adding an antacid to the ocean,” said lead author James Gately, a UC Santa Barbara doctoral student. Alkalinity, or basic compounds, changes the chemistry of seawater, shifting carbon dioxide.2 In other carbon compounds, such as carbonate and bicarbonate ions. This enables the oceans to absorb more carbon dioxide while reducing the acidity of the water.

In fact, this mechanism forms the basis of the geological carbon cycle, which recycles carbon between the land, atmosphere, and oceans over long periods of time. “Normally, this process takes tens to hundreds of thousands of years to happen,” Gately said. Our goal is to speed up this process.”

The driving question for Gately and colleagues is how will marine life respond to enhanced ocean alkalinity on large scales? To get the answer, they looked at how this treatment affected two major groups of plankton: diatoms and coccolithophores.

Both groups are important primary producers, converting sunlight into food and serving as the basis of the food chain in the ocean. “They play a key role in the biological carbon pump, the way the oceans lock carbon dioxide away from the atmosphere over millions of years,” said Professor Deborah Iglesias Rodriguez, Gately’s advisor in the Department of Ecology, Evolution and Marine Biology. These plankton also build exoskeletons, which means they transport huge amounts of calcium, silica, and carbonates around the biosphere.

Annual phytoplankton (eg, coccolithophores and diatoms) thrive small fish etc. along the food chain. After flowering, the dead cells fall to the sea floor, forming a sediment rich in carbonates or silica. Over time, these sediments sequester carbon from the atmosphere that organisms have assimilated through photosynthesis. Eventually, seafloor sediments can become rocks and limestone. If enhanced ocean alkalinity affected any of these plankton, the consequences could be dire.

The team added nutrients and alkalinity to the water they collected from the Santa Barbara Canal. Minerals such as olivine and various carbonates typically provide alkalinity over geological time, but Gately and his colleagues mimicked this process with other compounds that melt and react more quickly. Then they filtered the water to sterilize it before it was released into the air with 420 parts per million (ppm) of carbon dioxide, which is roughly equivalent to the carbon dioxide in the modern atmosphere.2 concentrations. A few days later, the team added diatoms and coccolithophores that they had grown in the lab.

The alkalinity of the modern ocean is between 2,300 and 2,400 small moles per kilogram of water. The scientists ran one experiment at 3,000 μmol/kg to simulate long-term alkaline addition and another at 5,000 μmol/kg to simulate potential hot spots, such as the treatment site.

The authors measured a range of changes in planktonic physiology and biochemistry, as well as seawater chemistry. They were particularly curious about whether the coccolithophores would increase their calcification, since the treatment would increase the abundance of calcium ions in the water. Ironically, the production of calcium carbonate actually produces carbon dioxide2, although the compound contains carbon and oxygen. Over long periods of time, the sequestration effects win out, making coccolithophores one of the largest carbon sinks on Earth.

Finally, plankton had a neutral response to alkaline treatments, and calcification did not change significantly. The photosynthetic efficiency of the cells decreased slightly, but remained within healthy levels for both treatments. The authors speculate that this decrease may be due to a decrease in the availability of micronutrients, such as iron.

In fact, the team observed that dissolved ions turn into solid compounds, or precipitate, at higher alkalinity levels. This process can remove nutrients and alkalinity from the solution, which can affect marine life and reduce the effectiveness of improving ocean alkalinity. The team is already investigating the process in new experiments.

“Finally, when we increased the alkalinity in the water, the physiology of these organisms did not change,” said Iglesias Rodriguez. While the results are encouraging, the authors caution against extrapolating to the ecosystem scale, because responses can vary across species. “Phytoplankton is a good start, but we need to test this in other organisms and ecosystems as well.”

The group has already begun performing alkalinity improvement experiments on entire planktonic communities under normal nutrient concentrations. They will measure the response of individual species as well as the community as a whole. Eventually the team plans to take the research out of the lab and into the field. “It’s very exciting, but we need to work with caution,” said Iglesias Rodriguez.

Like many geoengineering proposals, improving ocean alkalinity is a controversial topic. “We’re not saying this is a good idea, we’re trying to determine whether or not it is,” Gately said.

The problem is that it is too late to rely simply on reducing our emissions if we want to keep warming below 2°C. Expanding decarbonization to a gigaton scale will require several approaches; Improving the alkalinity of the ocean is just one of them. “None of these technologies are silver bullets for climate change,” Gately said, but the oceans sequester more carbon than the land and atmosphere combined, which makes ocean-focused approaches attractive.

However, geoengineering alone cannot solve the problem unless society reduces greenhouse gas emissions. “If we’re in a boat with a hole in it, we can use a bucket to try and draw water,” Gately added. “But if we don’t plug the hole, we’ll drown.”