Image from Ecofriend
Common sense tells us that if our kitchen sink is overflowing we should quickly turn off the tap before mopping up the floor. Despite this notion, it’s unclear whether the world will be able to cut ever-growing carbon emissions in half by the end of this decade in order to reduce the impacts of our warming climate. Rather than addressing emissions directly, public and private attentions shift to the controversial solutions in the field of geoengineering. Instead of solely emitting less, geoengineering suggests a manipulation of the climate in order to reduce the effects of climate change. Continuing the metaphor, geoengineering would be like adding different sponges to the overflowing sink, allowing the water to flow but reducing the likelihood of a mess. There are many different implementations of this idea such as solar radiation management, however, in this article I will focus on ocean iron fertilization (OIF) and how phytoplankton are a proposed solution to climate change.
Phytoplankton are microscopic marine plants that, like all other plants, use sunlight and carbon to photosynthesize. When these aquatic eukaryotic organisms die or get consumed, they carry the carbon they sequestered throughout their life to the bottom of the ocean in a process known as marine snowfall. The carbon is then locked away through mineral carbonation, stored for millions of years, and can only be returned to the atmosphere by periodic volcanic eruptions. This process is vital as a carbon sink when you consider that phytoplankton are responsible for capturing an estimated 37 billion metric tons of CO2 annually, the equivalent to about four times the amount sequestered by the Amazon rainforests’.
Phytoplanktons’ value is not limited to their ability to capture carbon, they also act as producers that form the foundation of most marine food webs. Phytoplankton is eaten by zooplankton, which in turn is eaten by jellyfish, then sea turtles, and so on until most marine organisms are affected. One study emphasized the importance of phytoplankton as a food source by showing that many marine invertebrates timed their breeding cycles with phytoplankton densities through direct coupling.
So, how are some proposing we capitalize on these microorganisms to help solve climate change? Research has shown that iron is the best macronutrient for phytoplankton growth and that by adding iron directly into the ocean, through iron seeding, phytoplankton populations will increase in tandem with their ability to sequester carbon. Iron would be intentionally poured in locations where nutrient concentrations are preventing phytoplankton from thriving. More phytoplankton means more carbon kept out of the atmosphere, thereby helping mitigate against climate change. Some early experimental models suggest that every one ton of iron added to the ocean could remove 30,000 to 110,000 tons of carbon from the air. Carbon emissions solved with biology doing most of the heavy lifting.
Unfortunately, the complexity of climate change cannot be solved with a simple solution.
Not all phytoplankton types are good, not all amounts are good for the environment, and the ocean is already very, very, good at its job.
One study reported that 60 to 80 species of phytoplankton are toxic, 90% of which potentially don’t sink and store carbon as well as others. For example, Pseudo-nitzschia produces toxic levels of domoic acid that can lead to mass mortality in various marine mammals, birds, and humans. When people consume shellfish exposed to domoic acid they are at risk for Amnesic Shellfish Poisoning (ASP), which can be life-threatening. Another study conducted over a 15 year period attributed a loss of approximately 500 million dollars in the US economy because of toxic phytoplankton affecting tourism, commercial fishing, public health, and environmental management costs.
When phytoplankton mass-reproduce on the ocean's surface, called blooms, they can occasionally create dead zones beneath them. Algal blooms cover the water surface, with millions of phytoplankton cells occupying any one gallon of water, preventing sunlight or oxygen from penetrating below. The phytoplankton eventually die off and sink to the seafloor, allowing oxygen to flow. However, the process of mass-decomposition requires all the surrounding oxygen and a hypoxic zone occurs. Light and oxygen are necessary for almost all marine life and so, as its morbid name suggests, dead zones created areas in which almost nothing can survive.
Iron concentrations in the ocean are so limited that it's a treasured nutrient to many species. One study published in 2020 found that most phytoplankton would not be able to utilize additional iron because the ocean already provides the correct amount of nutrients that maintain a self-reinforcing and self-sustainable balance of resources. Even if more iron was added to low-nutrient zones, the iron would likely drift to the seafloor unused since various nutrients, temperatures, and other conditions would not support the phytoplankton growth.
Despite these drawbacks, many are drawn to geoengineering techniques in order to clean up the mess of global carbon emissions. Many companies like Climos and Planktos Inc are hoping to make a profit off of carbon neutrality services based on iron fertilization. As it stands, iron fertilization is a controversial idea that is largely based on theoretical models and small-scale implementations. Before it becomes a tool to fight climate change on a larger scale, it must be discussed and researched in depth so that its pros and cons can be carefully considered. We must also ask ourselves if we’re using geoengineering as an excuse to keep up old habits and continue emitting without facing the consequences. There are no shortcuts or solutions without costs in the long run of climate change mitigation, and we must consider our options for carbon sinks while remembering to turn off our kitchen faucet.