A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration

51733385119_ac259b3ac0_o A Research Strategy for Ocean-based Carbon Dioxide Removal and Sequestration is a report from the USAnian National Academies of Sciences, Engineering, and Medicine. Apparently, they did a report in 2019 to provide a research agenda for advancing [Carbon dioxide removal] and, specifically, for assessing the benefits, risks, and sustainable scale potential for a variety of land- and coastal-based CDR approaches. The study found that, to meet climate goals, some form of CDR will likely be needed to remove roughly 10 Gt CO2/yr by mid-century and 20 Gt CO2/yr by the end of the century. To help meet that goal, four land-based CDR approaches are ready for large-scale deployment: afforestation / reforestation, changes in forest management, uptake and storage by agricultural soils, and bioenergy with carbon capture and storage, based on the potential to remove carbon at costs below $100/t CO2. I missed that, and my prior is that CDR is significantly more expensive that $100/t so perhaps I need to update my priors. Anyway, that was the land report, this is the ocean report. There was a solar geoeng one a half year back, which I barely skimmed, instead concentrating perhaps wrongly on the silly overreactions of some Big Knobs.

What did they consider? Here I'll list their starting points, together with my haven't-read-the-report reactions.

Nutrient fertilization (Chapter 3): Addition of micronutrients (e.g., iron) and/or macronutrients (e.g., phosphorus or nitrogen) to the surface ocean may in some settings increase photosynthesis by marine phytoplankton and can thus enhance uptake of CO2 and transfer of organic carbon to the deep sea where it can be sequestered for timescales of a century or longer. As such, nutrient fertilization essentially locally enhances the natural ocean biological carbon pump using energy from the sun, and in the case of iron, relatively small amounts are needed. 

WMC: seems sane.

Artificial upwelling and downwelling (Chapter 4): Artificial upwelling is a process whereby water from depths that are generally cooler and more nutrient and carbon dioxide rich than surface waters is pumped into the surface ocean. Artificial upwelling has been suggested as a means to generate increased localized primary production and ultimately export production and net CO2 removal. Artificial downwelling is the downward transport of surface water; this activity has been suggested as a mechanism to counteract eutrophication and hypoxia in coastal regions by increasing ventilation below the pycnocline and as a means to carry carbon into the deep ocean. 

WMC: sounds a bit mad to me.

Seaweed cultivation (Chapter 5): The process of producing macrophyte organic carbon biomass via photosynthesis and transporting that carbon into a carbon reservoir removes CO2 from the upper ocean. Large-scale farming of macrophytes (seaweed) can act as a CDR approach by transporting organic carbon to the deep sea or into sediments. 

WMC: also a bit wild-eyed but perhaps possible.

Recovery of ocean and coastal ecosystems (Chapter 6): Carbon dioxide removal and sequestration through protection and restoration of coastal ecosystems, such as kelp forests and free-floating Sargassum, and the recovery of fishes, whales, and other animals in the oceans. 

WMC: sounds rather limited.

Ocean alkalinity enhancement (Chapter 7): Chemical alteration of seawater chemistry via addition of alkalinity through various mechanisms including enhanced mineral weathering and electrochemical or thermal reactions releasing alkalinity to the ocean, with the ultimate aim of removing CO2 from the atmosphere. 

WMC: really?

Electrochemical approaches (Chapter 8): Removal of CO2 or enhancement of the storage capacity of CO2 in seawater (e.g., in the form of ions, or mineral carbonates) by enhancing its acidity, or alkalinity, respectively. These approaches exploit the pH-dependent solubility of CO2 by passage of an electric current through water, which by inducing water splitting (“electrolysis”), changes its pH in a confined reaction environment. As one example, ocean alkalinity enhancement may be accomplished by electrochemical approaches. 

WMC: sounds expensive.

Immeadiately after this is their key take-home message in the form of table S1 on pages 18-21. At least I hope it is, then I can stop reading early. Unfortunately, despite the need they assess for ~20 Gt/y, their "scalability high" is only "more than 1 Gt/y". But happily, that knocks out half of the ideas, leaving only fertilisation, alkalinity, and electrochemical. Coming to cost, of those three only fertilisation comes at under $100, so we have a winner. Well, that was quick.

What do you mean we're not finished? Well, of course not: these are people looking for research funds. Even hopeless ideas will still get something, of course. And at this stage that isn't too silly. Although why they want to shovel the most money at the weird electrochem stuff I don't know.

Although the fertilisation stuff is, as you'd expect, mostly about iron the PR puff says Nutrient Fertilization — This approach adds nutrients such as phosphorus or nitrogen to the ocean surface and mentions iron nowhere, which makes me doubt their good faith. The PR fluff is also careful to avoid any mention of scalability or relative cost of the different approaches.

The recommendations tip-toe around, both to avoid treading on anyone's toes by closing off people's pet ideas, and desperately (and pointlessly) trying to stop the zealots from screaming at them. Recommendation 3, includes "Research agenda that emphasizes advancing understanding of ocean fertilization, seaweed cultivation, and ocean alkalinity enhancement" which is a bit odd; it isn't clear to me why they picked those three.

So, in the end, meh: yes, you shoud do some reseach.


1. Pic by Nordin Catic at the Christmas Head. We're a scratch mixed VIII.


* Such evidence of arrogance, incompetence and poor judgment would reflect badly on any government - the Economist on Bojo the Clown.



Ocean fertilization used to be on the NAS short list of Things To Damn , witness this 2008 Science article. , at the end of which is my published response:


The reason it got bad ink back then was some antic ad hoc experiments that poured rust, rouge and ferrous sulfate over the transoms of tribal fishing boats and a rock star's yacht to promote plankton blooms designed to increase salmon catches as well as sequester carbon

The favor of link activation is requested

William M. Connolley said...

Alas I cannot edit comments here. But your link is https://www.science.org/doi/pdf/10.1126/science.318.5855.1368. Perhaps I should run an expensive beginners class in "how to write <a href=<url-in-quotes>>link text</a>". Meanwhile, I don't get to see your fine letter through the paywall... why don't you post it here, or some other public place so we can all benefit?

Belatedly, I realise that wiki has an IF article which tells me the last open-ocean experiment was 2012, which seems pretty pathetic to me.


Here it is - the paywall doesn't prevent copying the whole text

MAY. 12, 2008
Ocean Iron Fertilization
Russell Seitz

E. Kintisch's article, "Should oceanographers pump iron?" (News Focus, 30 November 2007, p. 1368)
reminds us that controversy surrounds ocean fertilization as a means of offsetting atmospheric carbon dioxide. Biologists are skeptical, because despite the late John Martin's famous assertion, "Give me a half tanker of iron and I'll give you an ice age" (1), many offshore areas sequester little carbon because their waters are perennially deficient in nitrogen and phosphorus as well.

But Martin's wish for a series of massive experiments may have been realized anyway—before he was born. During the decades before oil became the dominant marine transportation fuel, burning coal to raise steam at sea spewed literally megatons a year of iron, nitrogen, and phosphorous into nutrient-deficient surface waters.

Burning coal typically generates ash equal to ~10% of the fuel mass. In modern combustion technology, electrostatic precipitators, bag houses, and scrubbers remove over 95% of particulates. But no effort was made to capture fly ash in early marine propulsion, and about three-fourths was entrained and released with hot flue gases, the rest being incorporated into stack ash, boiler slag, and scoria (2).

Owing to the low energy density of coal relative to oil, the 50,000,000 ton fleet of coal-burning ships operating in the early 20th century (3) consumed many times its displacement in fuel annually. The efficient but ill-fated Titanic consumed 1.5% of its 42,000 tonne displacement daily, and lesser vessels typically combusted their displacement in bunker coal in a matter of months. The scale of marine fuel demand was such that Europe's 1913 export of 213 million tons of bunker coal represented less than half the world total (4).

Coal ash typically contains from 2.5% to 8.5% iron (5). Much occurs as pyrites (FeS2), and sulfate enrichment of ash particles by its oxidation may enhance the bioavailability of fly ash iron. This suggests that early 20th century European maritime activity alone annually released ~0.39 to 2.16 teragrams of iron at sea, with a high and frequently replenished aerosol iron flux along heavily traveled shipping lanes.

But what of nitrogen and phosphorus? Before the Haber process revolutionized nitrogen fixation, one of the most important fertilizers was the ammonium sulfate inevitably co-produced with coal tar in gas works and coke ovens. Since ship's coal typically contains 1 to 3% nitrogen, mostly in polycyclics, the pyrolysis yield of water-soluble pyrroles, pyridine and ammonium compounds from combustion at sea, may also have been in the low-teragram range. Unlike metallurgical coal, the ash of coal mined to raise steam typically contained on the order of a kilogram of phosphorus per ton.

This suggests that the co-deposition of nutrient phosphorus and nitrogen with iron may have at least locally met the N-P-Fe synergy criterion for enhancement of carbon fixation. Given that literal shiploads of fly ash fell at sea for decades, understanding what exactly was combusted along historic shipping lanes may shed light on the risks and benefits of the more modest CO2 sequestration experiments of today, and perhaps add the record of another historic aerosol (6) to the list of those already known to impact climate model estimates of 20th century and future radiative forcing.

Russell Seitz

Cambridge, MA 02138, USA.


1. J. H. Martin et al., Nature 371, 123 (1994).

2. U.S. EPA Radiation Protection (http://www.EPA.gov/rpdweb00/tenorm/coalandcoalash.html).

3. Lloyds Register (http://www.coltoncompany.com/shipping/statistics/wldflt.htm).

4. J. F. Bogardus, Geographical Review 20 (4), 642 (1930).

5. S. K. Gupta, T. F. Wall, R. A. Creelman, R. P. Gupta, Fuel Processing Technology 56 (issues 1–2), 33 (1998).

6. R. Seitz, Nature 323, 116 (1986).

William M. Connolley said...

Interesting. Thank you. Are you aware of anyone subsequently attempting to investigate this?


It has recently come to the attention of the groups that published on the algal blooms fertilized by iron fallout from last year's smokey Austalian wildfires , some plumes and blooms extended as far as the South Atlantic