Guest essay by Eric Worrall
Taiwanese researchers have poured cold water on the possibility of capturing carbon with artificial algae blooms, created by fertilising the oceans with iron. The problem appears to be that the artificial algae bloom depletes other essential ocean nutrients, causing a reduction in algae growth elsewhere in the ocean.
To alleviate the impact of global warming, scientists have proposed a hypothesis of “iron fertilization,” assuming that adding iron into the ocean can boost the growth of algae to absorb the carbon dioxide in the air.
However, researchers in Taiwan have found flaws in this hypothesis.
Working with Columbia University, a NTU research group led by Haojia Abby Ren, associate professor of Geosciences at National Taiwan University (NTU), has poured iron into 12 waters around the globe to perform experiments on the “iron fertilization” hypothesis. It turned out algae only thrives in one-third of the areas tested.
The growth of algae requires nutrients other than iron, such as nitrate and phosphate. With the growing amount of algae, consumption of these nutrients also increases in the area. But when currents carry the algae to other waters, the nutrients become relatively scare elements, making algae hard to grow.
This claim is backed by an earlier study, which suggests that increased iron outflows into the ocean during the last ice age, caused by glaciers scraping iron rich minerals into the sea, did not increase algae growth in equatorial regions, because increased algae growth in subantarctic zones depleted other ocean nutrients.
The abstract of the study;
No iron fertilization in the equatorial Pacific Ocean during the last ice age
The equatorial Pacific Ocean is one of the major high-nutrient, low-chlorophyll regions in the global ocean. In such regions, the consumption of the available macro-nutrients such as nitrate and phosphate is thought to be limited in part by the low abundance of the critical micro-nutrient iron1. Greater atmospheric dust deposition2 could have fertilized the equatorial Pacific with iron during the last ice age—the Last Glacial Period (LGP)—but the effect of increased ice-age dust fluxes on primary productivity in the equatorial Pacific remains uncertain3, 4, 5, 6. Here we present meridional transects of dust (derived from the 232Th proxy), phytoplankton productivity (using opal, 231Pa/230Th and excess Ba), and the degree of nitrate consumption (using foraminifera-bound δ15N) from six cores in the central equatorial Pacific for the Holocene (0–10,000 years ago) and the LGP (17,000–27,000 years ago). We find that, although dust deposition in the central equatorial Pacific was two to three times greater in the LGP than in the Holocene, productivity was the same or lower, and the degree of nitrate consumption was the same. These biogeochemical findings suggest that the relatively greater ice-age dust fluxes were not large enough to provide substantial iron fertilization to the central equatorial Pacific. This may have been because the absolute rate of dust deposition in the LGP (although greater than the Holocene rate) was very low. The lower productivity coupled with unchanged nitrate consumption suggests that the subsurface major nutrient concentrations were lower in the central equatorial Pacific during the LGP. As these nutrients are today dominantly sourced from the Subantarctic Zone of the Southern Ocean, we propose that the central equatorial Pacific data are consistent with more nutrient consumption in the Subantarctic Zone, possibly owing to iron fertilization as a result of higher absolute dust fluxes in this region7, 8. Thus, ice-age iron fertilization in the Subantarctic Zone would have ultimately worked to lower, not raise, equatorial Pacific productivity.
It might still be possible to deplete atmospheric CO2 using algae blooms, but you would have to somehow ensure the blooms received a balanced diet, and didn’t deplete the rest of the ocean of other essential nutrients. Manufacturing some essential fertiliser nutrients, such as nitrates, is extremely energy intensive.
Perhaps we should build more coal power plants, to produce the balanced algae fertiliser required to safely fixate all that carbon.