2.9: Oceans - fertilization

Iron fertilization

You might see these approaches referred to as OIF or Ocean Iron Fertilization

Some useful resources:
There is an existing regulatory framework for this called the London Protocol / London Convention:
After a new National Academies Report on “A Research Strategy for Ocean based Carbon Dioxide Removal” came out featuring a recommended $280M investment in research into the science underlying ocean iron fertilization, Science did a news feature on the topic

See also: OceanVisions roadmaps, which so far have mostly been on alkalinity enhancement and macro-algae, but presumably soon will extend into microalgae / OIF
Some proposals seek to induce growth of certain phytoplankton in the ocean, by seeding with various kinds of fertilizers, e.g., iron

Any old iron?
SIR--Martin and Fitzwater suggest that the growth of phytoplankton in ocean waters at high latitudes is restricted today by the limited amount of iron available, and that during recent ice ages the carbon dioxide content of the atmosphere was reduced because there was then more dust in the air. This suggests a possible way to alleviate the anthropogenic greenhouse effect, which is at present a cause for concern. By adding iron compounds to the oceans, a 'technological fix” to remove carbon dioxide from the air might be practicable. JOHN GRIBBIN

The costs would be very favorable in theory. Say the iron costs $1000/ton and one iron atom fertilizing the ocean allows 10,000 CO2 molecules to be captured into biomass. That works out to ~10 cents per tonne of CO2 fixed, 1000x smaller than the approximate theoretical best case cost for industrial direct air capture. Even if the cost were 10x higher than that, it would still be much less expensive than industrial direct air capture or ocean liming.This article suggest 30 cents per tonne CO2 capturedThis low cost also means that the efficiency of permanent sequestration of the fertilized biomass needn’t be anywhere near 100%.

The Lawrence paper says:

“while early studies indicated that CO2 removal by OIF might be capable of far exceeding CDRref, later studies showed that this neglected many limiting factors, so that the removal capacity is likely less than 400 Gt(CO2) by 2100 47. Furthermore, this would likely result in significant side effects in the oceans, like disruption of regional nutrient cycling, and on the atmosphere, including production of climate-relevant gases like N2O 15”.

Something a bit like this happened here, with the algae being eaten by shrimp rather than sinking down deep to sequester their carbon. A later study circumvented this problem by operating in a region where hard-shelled diatoms were stimulated to grow, rather than normal plankton, and these were less easy for the shrimp and such to eat, and thus apparently managed to sink the carbon to the ocean floor. In experiments with iron fertilization, blooms reduced the local partial pressure of CO2.There is some concern that the effects of this intervention may be short lived as a lot of the fixed carbon may just quickly re-enter the atmosphere

On the other hand, this article notes some interesting paleo-climate and ecological twists on iron fertilization that suggest that perturbations to ocean iron may not be so unusual and even that ocean iron may be at lower levels than usual at present:Another worry in my mind about modifying ocean nitrates or iron or so on, though, is that it could be dangerous in terms of changing the habitats for other creatures, like the cyanobacteria, which George Church reports in his Edge essay are finnicky as to their environment.

Moreover, one must be careful as to which nutrients are actually limiting or could become limiting. Ken Caldeira, in a talk, estimates that 1 additional iron atom can lead to ~50k additional carbon atoms incorporated into biomass, but within a few years this depletes P and N, and thus slows down the effect. He estimates that realistic iron seeding could not offset current emission levels.

It looks like Mount Pinatubo’s eruption in the early 1990s may have done ocean iron fertilization naturally and thus briefly stalled CO2 accumulation in the atmosphere. Likewise, recent big Australian wildfires seem to have caused a bloom.Coming back to the issue of side effects, notable ones of concern would include, I think increased nitrous oxide production by bacteria, selection for other microbes that produce greenhouse gasses once iron limitation is lifted, depletion of nutrients and oxygen that are needed by other species or that would later upwell in other locations

This article lays out more objections to iron seeding, including the idea that there is scale dependence and thus that you’d need to do large scale experiments that potentially themselves have side effects, in order to test for side effects in a way that’s realistic.

The key questions for this approach are:

  1. Why does iron fertilization sometimes lead to carbon drawdown and sometimes not?
  2. How can any negative side effects, especially long-term, of such an approach, be mitigated?

Non-iron fertilization

It seems that if one were to pursue ocean fertilization, you would not want to just fertilize with iron, but with a potentially dynamic and adaptive cocktail of different nutrients and do it in an adaptive way where you were measuring, perhaps with meta-genomics, the effects on different populations of organisms when you turn it on or off and then as the populations adjust. In one paper they suggest basically this:

“It has been proposed that fertilizer cocktails of macro- and micronutrients should be manufactured on land and transported by submarine pipe to a region significantly beyond the edge of the continental shelf. The nutrient ratios and the temporal supply rates could be controlled so that biological populations develop that optimize sequestration. Such environmental manipulation is today carried out in a sophisticated manner in terrestrial glasshouses where the physical conditions can be controlled, but, with close monitoring, there is no a priori reason why this should not also be possible in an environment such as the open ocean where control of the physical environment is unlikely to be possible.”

For better or worse, the coccolithophores seem to do OK with ocean acidification. On the flip side, other weird organisms can play a big role in sequestration by making and discarding “mucus houses”. Biology is crazy.Sometimes, there are also counterintuitive effects of biological growth, not all of it good for carbon sequestration. The Caltech course lecture 15, for example, points out that:

“In addition to organic carbon formed in photosynthesis, many organisms build calcium carbonate shells, CaCO3 (e.g. corals). Cocaliths (primary) and foraminifera (heterotrophs) produce large amounts of calcium carbonate and this carbon often drops to the bottom of the oceans. It is perhaps tempting to think that in forming these shells carbon is being driven out of the ocean system and that this would in turn draw down CO2. This is not the case, however. If we look at the expression for the interaction of atmospheric CO2 and DIC, we see that CO3 2- and CO2 are on the left of the expression. Le Chatelier’s principle tells us that if we remove CO3 2- (decrease alkalinity) we will drive CO2 out of the ocean. Growing corals increases atmospheric CO2. Growing cocaliths and foraminifera can pump carbon into the deep ocean depending on the ratio of organic carbon to CaCO3 in the falling matter. This ratio is known as the “rain ratio” and in the modern ocean is thought to be ~ 4.”

Below are some different non-iron approaches we could take.

Nutrient upwelling

Increasing nutrient upwelling through wave driven pumps is another interesting approach to promote more photosynthesis in the oceans. The nutrient upwelling site also explains that primary productivity in the ocean may be in decline due to global warming that has already occurred, proposing nutrient upwelling as a way to counteract this. This also promotes food security by increasing the fish catch. See this podcast on Marine Permaculture.

MacKay has a nice image showing the area of fertilized ocean that would be needed to neutralize Britain’s CO2 output:

Scale of nutrient upwelling for UK cdr

Clay minerals

Mukul Sharma has an interesting approach based on clay minerals which would help biomass to sink but not necessarily stimulate and alter ecosystems in the same way as seeding iron:

“Sharma’s idea is to use clay minerals to reduce the efficiency with which carbon is oxidized near the ocean surface by speedily burying it to great depths. After hitting the water, the minerals, which are dense, charged, and have large surface area, would pick up organic material and then fall quickly to depths low enough to take the carbon out of circulation with the atmosphere. Depending on which minerals are used, the process might also create material that zooplankton mistake for food and then excrete.”

At the same time, one has to ask for this approach: how much clay do you need to make a dent? Does this decrease the solar penetrance of the ocean via a self-shadowing effect? Does this enhanced sinking or recalcitrance mess up other food chains if you don’t add more biomass faster?