HOW MUCH CARBON DIOXIDE CAN WE LOCK IN THE DEEP OCEANS?

HOW MUCH CARBON DIOXIDE CAN WE LOCK IN THE DEEP OCEANS?

Aaron Dorman, Dec. 16, 2018 –

Natural ocean biology can help remove carbon dioxide from the atmosphere by trapping it in surface algae that sinks to the bottom of the sea. That’s the focus of research by two Columbia University scientists. These studies concluded that iron fertilization of the oceans surrounding Antarctica had occurred in the past to speed up the carbon trap, and that this could be happening again as ice sheets break up and glaciers melt.

And the two researchers with Columbia’s Lamont-Doherty Earth Observatory – Kassandra Costa and Jennifer Middleton- speculate that seeding the ocean with iron could stimulate more carbon uptake.

According to Costa, high-nutrient content in the Pacific sub-Arctic—the area underlying the Alaskan and Siberian coast—represented “unutilized biological capacity” for growing phytoplankton and trapping a portion of atmospheric carbon. Middleton’s research involves the Southern Ocean (or Antarctic Ocean), which is also high in nutrients but lacks one key ingredient to produce abundant carbon-consuming plankton: iron.

Ocean waters absorb much of the airborne carbon dioxide from fossil fuel emission, a carbon sink that has helped moderate air temperature rise across the globe but has fueled storms with warmer waters and is changing coral reef and marine habitats with acidifying waters. But the biological trap would remove the carbon with permanent burial in the sea floor.

The basic science of this process has been understood by climate researchers for several decades now: if less productive parts of the ocean were seeded artificially with iron, the resulting algae blooms could make an impact on removing atmospheric carbon dioxide.

Middleton, who began her post-doctoral research at Lamont-Doherty last December, explained at the annual Comer Climagte Conference in fall that the surface of the ocean is broken up into latitudinal bands, based on their nutrient content that is in turn partly related to geography. In the tropics, dust blows from the continental deserts, like the Sahel and the Sahara into the Atlantic Ocean.

“The record we’re looking at and building of past climate show that there’s likely to be an influence of increased iron and increased biological productivity in carbon export,” Middleton says. “But these are over much longer time scales and the iron being dumped in the ocean is sustained for decades, hundreds or even thousands of years.”

Middleton says that current studies have proven we they can use iron to turn carbon dioxide into organic material in the presence of algae, but it’s less certain how much of that will sink out of the ecosystem. “The modern day studies are useful,” Middleton says, “but we need a little bit more information to know if this is a sustainable long term solution.”

In the past, scientists believe that approximately 40 parts per million of carbon dioxide was sequestered in the deep oceans. A recent study published in Frontiers in Marine Science estimates that fertilizing the oceans now could sequester slightly less than that over a period of about 100 years. The amount of carbon dioxide this process could remove from the atmosphere is limited by other nutrients the algae needs, however, and atmospheric carbon dioxide levels have topped 400 ppm with fossil fuel emissions. Carbon dioxide, a greenhouse gas that holds heat in the atmosphere, is a thermostat for global warming.

Geological record of nutrients in the Northern Pacific. (Photo courtesy of Kassandra Costa)
Increased nutrient content in the Northern Pacific. (Photo courtesy of Kassandra Costa)

Earlier this month, the IPCC delivered another dramatic reminder that the uncertainty over disastrous global climate change is shrinking – and so is the time frame we have to control it. With the necessary atmospheric carbon draw down difficult to achieve in a short period of time, some scientists have pointed to geo-engineering, or human manipulation of the environment, as a solution. Artifially seeding the ocean with Iron is a form of this, though the most common project discussed is seeding the Earth’s atmosphere with aerosols that counteract the warming by greenhouse gasses.

The “grandfather” of climate science, Columbia Univesity’s Wally Broecker who helped helped coin the term “global warming” in the 1970s, says he believes some form of geo-engineering, most likely the atmospheric option, may be inevitable as at least part of the climate change solution.

“I think we are stuck,” Broecker says. “There’s no way in hell we’re going to pull that CO2 out of the atmosphere in a short time scale. There’s no way in hell we’re going to drop fossil fuel energy production by a factor of 10 in any short time.” So what are you going to do? “Is there a magic switch you pull? Boom! We stop raising CO2 and the earth cools and it doesn’t warm anymore? Forget it!”

Glaciologist Richard Alley speaks during the 2018 Comer Climate Conference

Broecker helps organize the Comer Conference each year. Richard Alley, another organizer and glaciologist at Penn State is the author of “Earth: The Operators Manual,” the title of both the book and a PBS mini-series. Alley says he worries about potential adverse effects from ocean iron fertilization, however. “You don’t get very far before you’ve changed the biology of the ocean,” Alley says. “You start running out of oxygen in places, and it starts coming back up—belching out nitrous oxide or something–and you haven’t really solved the problem.”

Despite the novelty of many proposals to engineer the planet as a fix for climate change, Alley believes the best long-term solution remains just stopping emissions of carbon dioxide into the atmosphere. “My personal opinion, from what has come out of the research so far, is that the easiest path really is moving towards a sustainable energy system,” he says.

Alley adds that the build-out of alternative energy systems promises a boom for the economy.

Photo at top: Could waters like these be seeded with iron to grow algae? Photo courtesy of Jennifer Middleton.


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