Ocean Fertilization — Will It Be a Solution to Climate Change or a Marine Calamity?

Scientists are in a race against time to reduce atmospheric carbon dioxide (CO2) and to try to prevent an increase in temperatures that would make our life on Earth miserable, if not unlivable. All manner of industries have proposed a range of potential solutions, several of which involve the ocean. These are referred to collectively as marine geoengineering and include techniques such as:

· Cloud seeding, whereby ships spray seawater to form reflective clouds

· Utilizing reflective foams or films on the ocean surface to reflect sunlight

· Alkalization, whereby alkaline powder that absorbs CO2 is pumped into the ocean

· Artificial upwelling, or pushing up cold water from the ocean depths to cool the surface

· Injecting CO2 into the ocean’s mid-waters, seabed, or sediment

One promising technique is ocean fertilization, which is the cultivation of plankton to absorb CO2 and then sink to the ocean floor, trapping the CO2 in the seabed.

How Does Ocean Fertilization Work?

In lay terms, ocean fertilization involves intentionally stimulating the natural process of photosynthesis carried out in the ocean by phytoplankton. Phytoplankton are microscopic marine algae that are the base of the marine food chain. They consume CO2, but their production is limited by the availability of micronutrients such as iron and zinc and macronutrients such as nitrogen and phosphorus.

Ocean fertilization involves adding nutrients to the ocean’s surface and employing techniques that propel nutrient-rich deep seawater closer to the surface. The nutrients stimulate phytoplankton blooms that absorb CO2 and release oxygen. Once the blooms die, the carbon-rich debris particles sink to the bottom of the ocean, potentially sequestering their carbon for centuries.

Iron Fertilization Experiments

Many marine geoengineering proposals are purely theoretical. However, there have been small-scale experiments with iron fertilization in each of the major iron-limited regions of the global ocean.

In 2004 the European Iron Fertilization Experiment (EIFEX) sowed iron sulfate over 167 km2 of the Southern Ocean in an iron-poor but otherwise nutrient-rich area. The research team monitored results and found photosynthesis by the resultant algae growth pulled 13,000 carbon atoms from the atmosphere for each iron atom added. They also reported that at least 50 percent of this carbon subsequently sank to below 1,000 meters within the stable eddy of the Antarctic Circumpolar Current. Beyond the eddy, the carbon capture was much less significant.

A 2009 experiment, LOHAFEX, received approval to fertilize a 300 km2 area of ocean in a remote location north of the Antarctic coast. This project met with limited success, however. Too late, it was discovered that the phytoplankton at the location were reliant on dissolved silicon to build cell walls, creating a protective shell — without this dissolved silicon they lacked protection and were therefore easier for other lifeforms to eat, nullifying any carbon-sequestering hopes.

Perhaps the most controversial of iron fertilization experiments was the 2012 Haida Gwaii iron dump in the North Pacific. Californian businessman Russ George deposited 120 tons of iron compound in salmon migration routes in an unsanctioned project purportedly to regenerate salmon fishing stocks. He claimed the exercise resulted in a phytoplankton bloom of 10,000 km2 and that he intended to use the process to produce and sell valuable carbon credits. The international marine community reacted immediately, accusing George of contravening the UN and London conventions on biological diversity and waste dumping, respectively. Both prohibit for-profit ocean fertilization activities. Many experts were also dubious about whether the bloom had been caused by George or had occurred naturally.

What Are the Long-Term Implications of Iron Fertilization?

Iron fertilization remains a highly contentious issue. The concerns around it have resulted in the current moratorium on the practice imposed by the London Convention in 2007. Stimulated blooming was shown to lead to the depletion of other nutrients, such as silica, in the LOHAFEX experiment. We also don’t yet know the long-term repercussions that deficiencies of nutrients like phosphorous or nitrogen will have on ocean health.

Additionally, some phytoplankton produce potent neurotoxins that can travel up the food chain and poison humans and other mammals. So, if fertilization stimulates the growth of the wrong phytoplankton, the consequences could be dire. All phytoplankton consume oxygen on death and decomposition, which results in oxygen-deficient zones within oceans. Further, we don’t know for sure how long the carbon in their remains will remain sequestered. But, on the other hand, stimulating phytoplankton could create the food sources necessary to stimulate our depleted fish stocks.

Ocean ecosystems tend to be highly interconnected, and trying to predict the effects of iron fertilization in both the short and long term is tricky. Plus, maintaining significant carbon drawdown through fertilization will likely require large-scale human, infrastructural, and financial capital. As a result, many experts are insistent that studies should be limited to naturally occurring blooms until we understand more about their longer-term effects. But others, like the staff at Woods Hole Oceanographic Institution, believe that controlled experiments need to continue. In the race to slow climate change, ocean fertilization could be one part of the solution.