This new paper on ocean micronutrients has revived my interest in a matter I raised in Science in 2006, as can be seen below
Fabrice Lambert
@fabricelambert.bsky.social
New paper alert!
We know CO2 drawdown is sensitive to iron micronutrient input. But how sensitive is it to the solubility of iron in mineral dust? Here is a sensitivity analysis using a carbon-centric EMIC for LGM and PI conditions.
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2025PA005132
MAY. 12, 2008
Ocean Iron Fertilization
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 flux of 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 that 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.
References
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).