Global Warming: Seed the ocean with iron?

[rhoenix]

On September 26-27, scientists at the Woods Hole Oceanographic Institution (WHOI) will host an international, interdisciplinary conference on the proposed “iron fertilization” of the ocean as a means to combat rising concentrations of greenhouse gases in the atmosphere.

Several times over the past century, scientists and environmental engineers have proposed spreading slurries of dissolved iron into the oceans in order to “fertilize” the waters and promote vast blooms of marine plants (phytoplankton). Phytoplankton consume carbon dioxide as they grow, and this growth can be stimulated in certain ocean basins by the addition of iron, a necessary micronutrient.

Though common on land, dissolved iron is often rare in the ocean. Some researchers and commercial interests have recently proposed to provide that missing nutrient on a large scale in order to create artificial blooms. Theory holds that if you make such blooms large enough, you could remove excess carbon dioxide from Earth’s atmosphere and carry it down into the deep ocean as organic matter (such as fecal pellets and dead plankton) sinks, thereby reducing the impact of greenhouse gases and global warming.

“There are many critical questions that require both better scientific understanding and an improved legal, economic, and political framework before iron fertilization can be considered either effective or appropriate,” said Ken Buesseler, a senior scientist in WHOI’s Marine Chemistry and Geochemistry Department and a participant in two iron fertilization experiments at sea. “The time is right to bring scientists, policymakers, and commercial interests together to inform each other and the public.”

Scientists took a serious interest in the idea in the late 1980s after oceanographer John Martin famously told colleagues: “Give me half a tanker of iron and I’ll give you the next ice age.” Iron fertilization has since been tested in at least a dozen experiments around the world. The results have varied, but in general, iron fertilizers have been shown to promote plant growth in surface waters. However, many researchers remain skeptical about whether the process removes carbon dioxide from the atmosphere for the long term or just for a fleeting time. Ecological impacts from long-term, large-scale fertilization are also a concern.

The purpose of the Woods Hole conference is to bring researchers, policymakers, industrial interests, regulators, and environmentalists together to share their scientific observations and discuss the range of issues involved in altering the chemistry of the ocean. It is not intended as forum or referendum for specific projects and ventures.

In 20 hours of formal presentations and panel discussions over two days, participants will discuss:

* Efficacy: Can iron fertilization work?
* Research: What do we already know, and what could future studies, models, and experiments tell us?
* Consequence: What will be the intended and unintended impacts?
* Policy: What are the economic, social, and regulatory considerations?

The symposium—“Exploring Ocean Iron Fertilization: The Scientific, Economic, Legal, and Political Basis”-- is being hosted by Buesseler, Scott Doney, a senior scientist in the WHOI Marine Chemistry and Geochemistry Department, and Hauke Kite-Powell, a research specialist in the WHOI Marine Policy Center.

The conference is an invitation-only event, but reporters and editors may view an archived webcast (starting September 27) at http://www.whoi.edu/conference/OceanIronFertilization.

WHOI also will host an open, public colloquium on iron fertilization at 2:30 p.m. on October 19 in the Redfield Auditorium on Water Street in the Village of Woods Hole.

Support for the iron fertilization conference was provided by the Elisabeth and Henry Morss Jr. Colloquia Fund, the Cooperative Institute for Climate Research, the WHOI Marine Policy Center, the Ocean and Climate Change Institute, the Ocean Life Institute, and Woods Hole Sea Grant.

Woods Hole Oceanographic Institution is a private, independent organization in Falmouth, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the oceans and their interaction with the Earth as a whole, and to communicate a basic understanding of the ocean's role in the changing global environment.

This is an interesting idea, and one that sounds plausible to me. Anyone have any other opinions or views?

[Hawkwings]

After the CO2 is at the bottom of the ocean, won't it slowly come back up?

Also, what are the ecological effects of a sudden bloom?

[Mayabird]

One of my profs was on the original study of iron fertilization in the Pacific, and he had a long lecture/rant about the whole hoopla around it.

Yes, they did get a big plankton bloom from iron fertilization. What most popular news articles conveniently leave out is
1) it was very difficult to actually get a concentrated bloom. The first time they tried, currents, wind, and all those other little intangibles meant they never got iron concentrations high enough in one area and it all just spread out to the rest of the ocean. They had to do a lot of work and a lot of weird boat manuevering to get the iron concentrations to work their magic.
2) All that plankton got eaten doublequick. The theory is that it's supposed to sink to the bottom and remove the carbon from the carbon cycle, but since it all got eaten and carried off, it could still return to the atmosphere when the fish that ate the fish dies.

To get any sort of noticable effect, someone would HAVE to fertilize a huge area of ocean to swamp all the native biota and keep them from eating everything and carrying the carbon off just to return to the atmosphere. That someone would ALSO have to make sure the carbon removal at least offsets the emissions that would result from all those ships chugging around dumping their iron in very carefully controlled manners. We don't even know that it would work to offset itself, much less what it could do to the environment if it did work according to plan.

Also, to Hawkwings: yes, it would come up eventually. The ocean has this deep water circulation thing which would eventually bring the carbon back up, and nobody really knows that much about it. Current theories, as far as I've seen, indicate that it could take tens of thousands of years, giving us time to fix things if we really screw up, but I'm by no means an expert in it so I don't really know.

[Mr Bean]

We need to blow up the ocean!

Seriously how about if we pick a rather large lake or inland sea and flood it? Say one of those great lakes. Forget the fishing, just dump half a million tons of iron in and let the plankton do the work?

[Mayabird]

We need to blow up the ocean!

Seriously how about if we pick a rather large lake or inland sea and flood it? Say one of those great lakes. Forget the fishing, just dump half a million tons of iron in and let the plankton do the work?

This is called eutrophication.

In lakes, it typically happens when too much nitrogen gets dumped in. Algae blooms like crazy, the thick green scum. The algae dies and sinks to the bottom, and bacteria go crazy breaking the algae down, sucking up all the oxygen in the lake. Effectively, the lake dies.

It's even happened in the Black Sea. It used to be a freshwater lake, and then the Bosporus broke through and flooded it with seawater. All the plants around the lake got flooded and killed and it all sank to the bottom, where the decay sucked out all the oxygen. Below a couple hundred feet, the whole sea is dead. Anoxic. Probably every ship that sank there since the sea came in is still preserved at the bottom because wood can't decay.

So yeah, doing this in anything inland wouldn't work.

[Surlethe]

This is awesome! We could seed the sea with iron and shoot giant sulfur crystals into the upper atmosphere with giant cannons. We can solve global warming just like that!

Hey, this thought just occurred to me. Instead of going to all the expense, trouble, and potential complications of these schemes, what if we just, you know, cut back on carbon emissions? Like weaning ourselves from our dependence on fossil fuels? What a novel thought.

[nightmare]

Also, what are the ecological effects of a sudden bloom?

Very serious. Algae blooming kills all macrolife, either directly by toxins, or indirectly, by bacteria feeding on decomposing algae and using up all oxygen. Sometimes the bacteria are also poisonous, preventing regrowth. You can pretty much spell "algae blooming" as "mass extinction".

[Sikon]

[...]

This is an interesting idea, and one that sounds plausible to me. Anyone have any other opinions or views?

It is a very interesting idea. But the topic runs into the average ideological tribalism, as it isn't politically correct to suggest using some geoengineering measures in addition to reducing CO2 emissions.

Also, what are the ecological effects of a sudden bloom?

Very serious. Algae blooming kills all macrolife, either directly by toxins, or indirectly, by bacteria feeding on decomposing algae and using up all oxygen. Sometimes the bacteria are also poisonous, preventing regrowth. You can pretty much spell "algae blooming" as "mass extinction".

That doesn't correspond to what is relevant here, which is a matter of increasing the primary productivity of some iron-deprived areas of the oceans to make them more like some other regions with more phytoplankton.

The productivity of the ocean varies a lot:



Iron fertilization could increase the primary productivity of some areas of the ocean currently suffering too much from a shortage of iron as a limiting nutrient, in areas where other nutrients are not so limited. For example, in other words, it could increase the amount of plankton, the basis of the marine food chain, to a degree making a small percentage of the blue areas in the above graph be lighter blue or cyan.

The following is an illustration of the general principle:

In the spring of 2001, two robotic Carbon Explorer floats recorded the rapid growth of phytoplankton in the upper layers of the North Pacific Ocean after a passing storm had deposited iron-rich dust from the Gobi Desert. The carbon measurements, reported in the October 25 issue of Science, are the first direct observation of wind-blown terrestrial dust fertilizing the growth of aquatic plant life.

A group of scientists led by oceanographer James K. Bishop of Lawrence Berkeley National Laboratory's Earth Sciences Division engineered the deep-diving Carbon Explorers to measure particulate carbon in the upper thousand meters of the ocean.

[...]
Two of the specially modified Carbon Explorers were launched April 10, 2001, from the U.S. Coast Guard's icebreaker Polar Star near Ocean Station PAPA, in subarctic waters a thousand miles west of Vancouver Island. The Carbon Observers were programmed to sample the depths and return to the surface three times every two days, regularly sending data to satellites overhead.

[...]
Phytoplankton growth is affected by factors like nutrient concentrations, light, temperature, salinity, and the way the sea water mixes. Earlier studies at PAPA suggested that growth in the region was also limited by a lack of dissolved iron in the water. The Carbon Observers would soon put that assumption to the test.

[...]
Testing the iron hypothesis
In the 1930s oceanographers first began to suspect that terrestrial dust storms play a key role in phytoplankton growth in the so-called high nutrient, low chlorophyl (HNLC) areas of the ocean, whose concentrations of dissolved iron, an essential micronutrient, are much lower than in other regions. By dissolving carbon in seawater and by fixing it as biomass or inorganic particulate matter, phytoplankton regulates carbon dioxide in the atmosphere and thus helps regulate global climate.

In the 1980s, oceanographer John Martin gathered these facts in his "iron hypothesis," which proposed that by fertilizing plankton growth with iron, global warming could be offset. Iron fertilization can indeed cause plankton "blooms" in HNLC waters, as several expeditions including Soiree (the Southern Ocean Iron Enrichment Experiment) in February 1999 and SOFeX (the Southern Ocean Iron [Fe] Experiment) in January and February 2002 have proved by pouring dissolved iron into HNLC areas in the Southern Hemisphere. But prior to the spring of 2001, fertilization by iron transported in terrestrial dust storms had never been observed directly.

[...]
Three days before the launch of the Carbon Observers on April 10, a NASA satellite recorded a large dust storm originating near the Gobi Desert in China and Mongolia; on the day of the launch, the dust cloud was over Japan and heading for the North Pacific. It reached Ocean Station PAPA on April 12, where it kicked up the waves and deposited a large amount of dust.

Although high waves temporarily kept the Carbon Observers from reporting by satellite, data collection continued uninterrupted through the storm. Five days after the storm passed, the floats reported rising concentrations of particulate organic carbon; the concentration almost doubled in the next two weeks.

Bishop notes that "the timing of this natural increase matched the timing of plankton growth after iron was artificially added to Southern Ocean waters during Soiree and SOFeX, a good indication that iron fertilization was the cause in the North Pacific as well."

From here.

This thread has been suffering from a shortage of appropriate data. Aside from the above introductory passage, let's begin with the following extracts from one paper:

The organisms responsible for photosynthesis at the ocean surface are phytoplankton. In addition to CO2 and water, they need nutrients such as phosphorus, nitrogen and iron to produce organic matter. The reaction is presented as follows [...]

This means that each unit of iron can fix 106,000 units of carbon, 16,000 units of nitrate and 1,000 units of phosphate. [In practice, the actual efficiency of adding iron is naturally less than the preceding, which would be more like the theoretical maximum, but there still is an orders of magnitude ratio of the mass of carbon fixed to the mass of iron appropriately used]. The quantity of iron needed is very small compared to the quantity of phosphate or nitrate [and relatively miniscule compared to the total mass of plankton grown]; but without iron, phytoplankton will not survive.

[...]
An observation of the annual phosphate as well as the annual nitrate (see figures 2.3 and 2.4) levels at the ocean surface shows that these nutrients are not uniformly distributed. We have areas where concentrations of nitrate and phosphate are close to zero and others with high concentration. The areas with the highest concentrations are the Southern Ocean and the Subarctic Pacific with 1.5 to 2.0 umol/kg, followed by the Arctic zone with 1.0 umol/kg. Normally, we expect those regions to be biologically very active [...] Curiously, some of them have a very weak population of phytoplankton. This can be seen by observing figures 2.3, 2.4 and 2.5 which shows that the Southern Ocean, the Surbarctic Pacific and the Equatorial Pacific, all regions of high nutrients concentrations, are very poor in chlorophyll (pigmentation due to photosynthesis carried by phytoplankton). Those regions are described as High Nutrients Low Chlorophyll (HNLC). The reason for this is the limited quantity of iron in these regions. This is due to the large distance between them and the large deserts (Kalahari, Sahara and Arabian deserts) which consequently cannot supply enough iron as they do for the rest of the ocean [10]. The North Atlantic is at the same latitude [similar sunlight levels] as the Subarctic Pacific but is supplied with quantities of iron dust from the Sahara desert in Africa. Consequently the North Atlantic is not an HNLC region. Iron comes into the ocean in the form of dust transported by wind and plays a vital role as a micronutrient for photosynthesis and the growth of phytoplankton.

[...]
A few months after the eruption of Mount Pinatudo in 1991 in the Philippines, the environmental scientist Andrew Watson analyzed global data from the eruption and calculated that it deposited approximately 4 × 10^10g [4E7 kg = 40,000 metric tons] of iron dust into the Southern Ocean [12]. The minerals were washed into the oceans, where the iron fertilized the plankton which enabled them to fix and metabolize more CO2. This fertilization event generated an observed global increase of O2 and decline of CO2 in the atmosphere [12], perhaps showing the evidence of Martin’s hypothesis.

[...]
NASA and NOAA estimate a decline of the phytoplankton population in the last 25 years of at least 6%. Simply returning this population to its previous levels of health and activity could therefore annually sequester 2 to 3 billion more tons of CO2 than are being removed today. Iron fertilization targets are areas that have persistently high levels of major nutrients, such as nitrate and phosphate, but are also weakly photosynthetic (HNLC) regions. An important example is the Southern Ocean, which has the largest repository of unused macronutrients in surface water, and plays a key role in the formation of intermediate and deep water [13]. These areas might represent a non-negligible ratio of about 16% of the total surface ocean [14].

From here.

As the article points out, not all areas of the ocean are suitable for iron fertilization. For example, much of the ocean has phytoplankton productivity limited by other limiting nutrients than iron, with many regions already receiving enough iron naturally from dust from land. However, as described, there are large areas where the iron fertilization effect observed from the Mount Pinatudo eruption might be emulated and indeed exceeded.

A key aspect is that the mass of iron required is orders of magnitude less than the amount of carbon fixed. Such would not be just a single tanker of iron by any means, but a few million tons of iron could affect up to billions of tons of carbon dioxide for an economically and energetically efficient high payback ratio. Incidentally, that's why the mass of fuel consumed and mass of CO2 emissions from ships depositing the iron is far less than the amount of carbon fixation from the fertilization, making the process of net benefit. And that's also what can make it exceptionally inexpensive per ton of CO2.

Iron fertilization is far more limited than some other geoengineering options for helping counter global warming, but it can have some benefit.

All that plankton got eaten doublequick. The theory is that it's supposed to sink to the bottom and remove the carbon from the carbon cycle, but since it all got eaten and carried off, it could still return to the atmosphere when the fish that ate the fish dies.

"All" is too simplistic. In recent studies, it has been estimated that just a moderate minority of the total biomass produced ends up sequestered, but that can still be a substantial amount, more than enough compared to the orders of magnitude lesser amount of iron used for a good payback ratio. For example:

We conducted four mesoscale in-situ iron fertilization experiments in the Southern Ocean and the subarctic North Pacific during 2001 and 2004 (Fig.1). Iron fertilization stimulated phytoplankton growth in all experiments. The water mass fertilized with iron was found to turn into absorption area of atmospheric CO2.

[...]
The amounts of biological carbon fixation were estimated quantitatively by the observed results of organic carbon stock and organic carbon flux in each experiment (Table 1). When vertical organic carbon flux at 100 m depth was assumed to be the amount of carbon fixation, the amount of carbon fixation was estimated to be approximately 16% of the increased organic carbon stock with iron fertilization.

From here.

Here's another estimate, with exact figures varying with factors like the particular situation but with this showing the general idea:

This CO2 contributes to the formation of organic matter which is expected to sink to the deep ocean. In fact, just approximately 30% of this carbon-rich biomass sinks below 200 meters into the colder water strata below the thermocline [4]. Part of this fixed carbon continues falling into the abyss and the rest is dissolved and remineralized. However at this depth, the carbon is suspended in the deep ocean and effectively isolated from the atmosphere for centuries.

From here.

What about the rest of the new biomass, the majority which just gets eaten? Naturally fish love eating plankton, but that relates to one of the interesting aspects of iron fertilization. With phytoplankton being the basis of the marine food chain, each additional billion tons of phytoplankton eaten by fish leads to a lot of extra fish being supported, which can be a very major advantage when such would be beneficial to reduce the depletion of the ocean fish population from human fishing.

More food for fish -> more fish -> more fish for people to eat.

As shown, the preceding is not mutually exclusive with iron fertilization having a carbon sequesterization effect because not all of the fixed carbon ends up in the same spot, not 100% being eaten.

Mankind already affects natural carbon fixation all the time, whether planting a tree or destroying a forest, whether increasing or decreasing ocean biomass. It's bad when a bias against implementing intentional beneficial measures makes the net effect consist too much of just the unintentional, accidental, negative effects alone.

There's not exactly a question whether or not mankind will perform geoengineering. Mankind already is doing so. The only question is whether all geoengineering will be the accidental kind or whether some will be more intelligently directed. Mankind already is performing an inefficient, negative form of geoengineering with CO2 emissions, and so far it is just unintentional geoengineering towards a net rise in temperature.

Of course, iron fertilization would not be suitable for being the sole measure against global warming. For example, it lacks unlimited scalability. However, if one avoids simplistic black/white assumptions like treating any countermeasure not the sole solution as worthless, iron fertilization may be beneficial as one of multiple measures, particularly because of the unusual side benefit of increasing the net primary productivity of some areas of the ocean ... allowing more fish.

Such could be combined with other measures. For example, it is possible to artificially increase carbon fixation on land as well as in the oceans: planting new forests, appropriately fertilizing some areas of land, etc.

Of course, mankind needs to switch away from fossil fuels as the energy source, but, realistically, there's the amount of radiative forcing from past emissions and some certain future emissions, which could use a variety of compensatory measures.

[Alyrium Denryle]

Iron fertilization could increase the primary productivity of some areas of the ocean currently suffering too much from a shortage of iron as a limiting nutrient, in areas where other nutrients are not so limited. For example, in other words, it could increase the amount of plankton, the basis of the marine food chain, to a degree making a small percentage of the blue areas in the above graph be lighter blue or cyan.

It is hardly irrelevant. If the goal is to preserve as much as possible the natural ecosystems on this planet, then nutrient polluting the oceans and causing an ecologically disastrous local extirpation of the local multicellular life is not a solution. We would not just cause algae blooms, but also increase bacterial loads and give lots and lots of food to dinoflagellates and create red tides.

I would also not use the words "suffering from a shortage of iron" because that implies that there is something wrong with those oglitrophic parts of the ocean. There isnt.

What about the rest of the new biomass, the majority which just gets eaten? Naturally fish love eating plankton, but that relates to one of the interesting aspects of iron fertilization. With phytoplankton being the basis of the marine food chain, each additional billion tons of phytoplankton eaten by fish leads to a lot of extra fish being supported, which can be a very major advantage when such would be beneficial to reduce the depletion of the ocean fish population from human fishing.

More food for fish -> more fish -> more fish for people to eat.

And what other ecological effects will this have? Artificially sustaining fish populations above and beyond what the environment would support without human interference in their populations does not seem to me tp be a wise decision from an ecological standpoint. Keep in mine I am a non-anthropocentrist and dont really give a damn about the economic impact of a reinvigoration of a fishing industry that causes a crapload of ecological damage independent of their fishing.

[Sikon]

Iron fertilization could increase the primary productivity of some areas of the ocean currently suffering too much from a shortage of iron as a limiting nutrient, in areas where other nutrients are not so limited. For example, in other words, it could increase the amount of plankton, the basis of the marine food chain, to a degree making a small percentage of the blue areas in the above graph be lighter blue or cyan.

It is hardly irrelevant. If the goal is to preserve as much as possible the natural ecosystems on this planet, then nutrient polluting the oceans and causing an ecologically disastrous local extirpation of the local multicellular life is not a solution. We would not just cause algae blooms, but also increase bacterial loads and give lots and lots of food to dinoflagellates and create red tides.

If you claim some additional iron reaching some HNLC areas of the ocean must result in ecological disaster, red tides, etc., where's the proof of your claim when such is not shown by the iron fertilization events mentioned in my post?

I'll even re-quote a few segments to make this more obvious:

In the spring of 2001, two robotic Carbon Explorer floats recorded the rapid growth of phytoplankton in the upper layers of the North Pacific Ocean after a passing storm had deposited iron-rich dust from the Gobi Desert.

[...]
Testing the iron hypothesis
In the 1930s oceanographers first began to suspect that terrestrial dust storms play a key role in phytoplankton growth in the so-called high nutrient, low chlorophyl (HNLC) areas of the ocean, whose concentrations of dissolved iron, an essential micronutrient, are much lower than in other regions.

[...]
Iron fertilization can indeed cause plankton "blooms" in HNLC waters, as several expeditions including Soiree (the Southern Ocean Iron Enrichment Experiment) in February 1999 and SOFeX (the Southern Ocean Iron [Fe] Experiment) in January and February 2002 have proved by pouring dissolved iron into HNLC areas in the Southern Hemisphere.

[...]
Three days before the launch of the Carbon Observers on April 10, a NASA satellite recorded a large dust storm originating near the Gobi Desert in China and Mongolia

[...]
Bishop notes that "the timing of this natural increase matched the timing of plankton growth after iron was artificially added to Southern Ocean waters during Soiree and SOFeX, a good indication that iron fertilization was the cause in the North Pacific as well."

From here.

A few months after the eruption of Mount Pinatudo in 1991 in the Philippines, the environmental scientist Andrew Watson analyzed global data from the eruption and calculated that it deposited approximately 4 × 10^10g [4E7 kg = 40,000 metric tons] of iron dust into the Southern Ocean [12]. The minerals were washed into the oceans, where the iron fertilized the plankton which enabled them to fix and metabolize more CO2. This fertilization event generated an observed global increase of O2 and decline of CO2 in the atmosphere [12], perhaps showing the evidence of Martin’s hypothesis.

From here.

It is a little like someone arguing one can't fertilize one's garden because pouring a thousand gallons of fertilizer on one plant can kill it ... when that is not how one actually carries out fertilization.

I like how this thread contains one anti-geoengineering post saying a problem is the plankton all being eaten by fish, while simultaneously the claims of other anti-geoengineering posts are contradictory to the fish being around, as they try to imply multicellular life is wiped out.

I would also not use the words "suffering from a shortage of iron" because that implies that there is something wrong with those oglitrophic parts of the ocean. There isnt.

It has less productivity than it could have. As an analogy, there isn't anything "wrong" with a barren stretch of land, but converting a few such areas to forests by planting trees is another carbon sequesterization strategy frequently suggested, for good reason.

And what other ecological effects will this have? Artificially sustaining fish populations above and beyond what the environment would support without human interference in their populations does not seem to me tp be a wise decision from an ecological standpoint. Keep in mine I am a non-anthropocentrist and dont really give a damn about the economic impact of a reinvigoration of a fishing industry that causes a crapload of ecological damage independent of their fishing.

If some iron-deprived HNLC areas receive an appropriate infusion of nutritional iron, such can make them more like some other areas of the ocean that already naturally have enough iron received from dust. The latter areas of the ocean have an acceptable ecology from the perspective of many interested in human welfare.

[Mayabird]

Sikon, the iron fertilization experiments have been done on small scales, insignificant to the size of the ocean. Doing enough fertilization to make an appreciable dent in global warming would require seeding a much, much larger area. I've seen estimates that the entire Antarctic ocean would have to be seeded. We just don't have the data to know what the results of such a huge project would be. We don't know much about deep ocean circulation. We know very little about the deep sea away from the hot vents. What we do have is examples of what happens in lakes and seas and of dead zones (which can be huge) at the mouths of rivers that see a lot of fertilization from agriculture.

Not to mention, most fish caught in the sea are thrown away as bycatch. Even if you do support larger fish populations without any drawbacks, those fish are mostly getting thrown away as trash and getting wasted anyway.

And this has nothing to do with ideological tribalism. You're talking to someone here who wants to start large-scale building of nuclear power plants for energy, including nuclear-powered desalination plants for deserts and areas that are undergoing desertification. Plus someone who wants to flood the Qattara Depression for hydroelectricity and nuclear-powered "water the Sahara" schemes. What I have issues with is people treating this like some sort of magic bullet. There are no such things as magic bullets in real life.

[Sikon]

Sikon, the iron fertilization experiments have been done on small scales, insignificant to the size of the ocean.

The effect of the Mount Pinatudo eruption mentioned was over a larger scale than the small experiments, though, and there's a lack of reason not to expect some trends to be similar whether over X or Y square kilometers.

I've seen estimates that the entire Antarctic ocean would have to be seeded.

Up to a few percent of total ocean area, suitable HNLC regions.

Well, strictly speaking, this wouldn't happen overnight anyway, taking years to ramp up, with the way it could occur being through being done on 0.01% of the ocean area before 0.1%, before 1%. Negatives would tend to become apparent early enough during the long process if such were really major, allowing time to counter before becoming too extreme, but the evidence is for benefits tending to outweigh negatives.

We just don't have the data to know what the results of such a huge project would be. We don't know much about deep ocean circulation.

The paper with its five-box model makes some good guesses, more likely than not to have some validity given past observations.

Not doing anything decade after decade is itself equivalent to an action with known major negative consequences.

Mankind would have died out long ago if people really followed a literal interpretation of the precautionary principle, not doing much of anything, including increasing land productivity through agriculture. It is probabilities that matter, for whether probable benefit most likely outweighs probable harm.

What we do have is examples of what happens in lakes and seas and of dead zones (which can be huge) at the mouths of rivers that see a lot of fertilization from agriculture.

That's not the result of an iron fertilization project. That's the result of unintentional concentrated runoff of millions of tons of nitrates into a relatively tiny area, quite different. Appropriate iron fertilization is designed to make some HNLC ocean regions more like some more productive regions.

Not to mention, most fish caught in the sea are thrown away as bycatch. Even if you do support larger fish populations without any drawbacks, those fish are mostly getting thrown away as trash and getting wasted anyway.

Unless there are references showing otherwise, most fish may be an overestimate, at least if one looks at this by mass. A quick check promptly finds one article here suggests possibly around 30 million tons of discards annually, versus around 80 million tons of ocean fish caught annually. But, in any case, it doesn't matter anyway for the main point of this discussion. Frequent human preferences regarding some creatures as inedible or unpalatable would be a separate topic.

And this has nothing to do with ideological tribalism. You're talking to someone here who wants to start large-scale building of nuclear power plants for energy, including nuclear-powered desalination plants for deserts and areas that are undergoing desertification. Plus someone who wants to flood the Qattara Depression for hydroelectricity and nuclear-powered "water the Sahara" schemes.

Good. But the ideological biases of large segments of the public are a rather different subject, with a single individual not being statistically significant for judging them.

What I have issues with is people treating this like some sort of magic bullet.

I haven't seen many people argue that, to say the least.