Planet Care

363: Iron fertilisation


Our planet is warming.


The more daring scientists are taking a more radical approach to cooling the earth’s climate, such as dumping iron dust into the ocean, hoping to grow algae blooms that suck up carbon. Iron fertilization is the intentional introduction of iron to iron-poor areas of the ocean surface to stimulate phytoplankton production.

This is intended to enhance biological productivity and/or accelerate CO₂ sequestration from the atmosphere. Iron is a trace element necessary for photosynthesis in plants. It is highly insoluble in sea water and in a variety of locations is the limiting nutrient for phytoplankton growth. Large algal blooms can be created by supplying iron to iron-deficient ocean waters. These blooms can nourish other organisms.

Consideration of iron’s importance to phytoplankton growth and photosynthesis dates to the 1930s when English biologist Joseph Hart speculated that the ocean’s great “desolate zones” (areas apparently rich in nutrients, but lacking in plankton activity or other sea life) might be iron-deficient.

Little scientific discussion was recorded until the 1980s, when oceanographer John Martin renewed controversy on the topic with his marine water nutrient analyses. His studies supported Hart’s hypothesis. These “desolate” regions came to be called “High Nutrient, Low Chlorophyll” (HNLC) zones.

John Gribbin was the first scientist to publicly suggest that climate change could be reduced by adding large amounts of soluble iron to the oceans. Martin’s 1988 quip at Woods Hole Oceanographic Institution, “Give me a half a tanker of iron and I will give you another ice age”, drove a decade of research. Perhaps the most dramatic support for Martin’s hypothesis came with the 1991 eruption of Mount Pinatubo in the Philippines.

Environmental scientist Andrew Watson analyzed global data from that eruption and calculated that it deposited approximately 40,000 tons of iron dust into oceans worldwide. This single fertilization event preceded an easily observed global decline in atmospheric CO₂ and a parallel pulsed increase in oxygen levels.

Beginning in 1993, thirteen research teams completed ocean trials demonstrating that phytoplankton blooms can be stimulated by iron augmentation. Controversy remains over the effectiveness of atmospheric CO₂ sequestration and ecological effects.

In Spring 2004, an international team on board the 386 ft 10 in (117.91 m) RV Polarstern (meaning pole star) of the Alfred Wegener Institute for Polar and Marine Research (AWI) in the Helmholtz Association, Bremerhaven, fertilized a part of the closed core of a stable marine eddy in the Southern Ocean with dissolved iron, which stimulated the growth of unicellular algae.

The team followed the development of the phytoplankton bloom for five weeks from its start to its decline phase. The maximum biomass attained by the bloom was with a peak chlorophyll stock of 286 Milligram per square metre higher than that of blooms stimulated by the previous 12 iron fertilization experiments.

According to Dr. Victor Smetacek and Dr. Christine Klaas from the Wegener Institute, this was all the more remarkable because the EIFEX bloom developed in a 3330 ft  (1000 m) deep mixed layer which is much deeper than hitherto believed to be the lower limit for bloom development.

In early 2009 a further dumping of 20 tons (18 tonnes) of ferrous sulphate by Victor Smetacek, called LOHEFEX (LOHA is Hindi for iron, FEX stands for Fertilization EXperiment) was suspended by the German Federal Ministry of Education and Research (BMBF) demanding that an independent assessment into the environmental impacts of the experiments be carried out before the ferrous sulphate is dumped in the Southern Ocean.

Greenpeace and other environmental organizations demanded from the start that LOHAFEX be stopped, saying that pouring iron into the ocean amounted to pollution and violated international agreements. Some scientists feared the unintended side effects of the project. The German Government sent the proposal for scientific and legal reviews that were supportive of the project and the experiment was allowed to continue.

Other trials have continued. In 2012, the Haida Salmon Restoration Corporation (HSRC), financed by a First Nations community from the British Columbian archipelago, Haida Gwaii, conducted a small scale Ocean Fertilization experiment where 120 tons (109 tonnes) of iron compound were deposited in the migration routes of pink and sockeye salmon in the Pacific ocean West of Haida Gwaii over a period of 30 days.

The project resulted in a 14,000 mi² (35,000 km2)  plankton bloom that lasted for several months and was confirmed by NASA satellite imagery. The HSRC scientific team collected a significant amount of oceanographic data using autonomous underwater vehicles (Slocum Gliders), Argo Drifters, Multi-Spectral Sonar, Surface Seawater samples, Phytoplankton Tows and other methods.

The Desarc-Maresanus project, led by Professor Stefano Caserini, Professor of Mitigation of Climate Change at Politecnico di Milano, in collaboration with the Foundation Euro-Mediterranean Center on Climate Change (CMCC) with support of Amundi, consists in discharging alkaline products (i.e. limestone or slaked lime) in the sea, increasing the pH of the water favoring a greater absorption of CO2 from the sea surface.

This is known as ocean alkalinisation and has been carried out by ships whose great turbulence caused by the propeller and by the ship’s wake great improves dispersal.

In 2019, researchers at the University of Hawaii and University of Southern California published a report which stated that following the previous year’s eruption of Kilauea, the incredible volume of lava that spewed from the ground as not only a source of destruction but of creation.

It looked at the massive algae bloom in the Pacific ― so big it could be seen by satellite ― that was triggered by millions of cubic ft. of lava pouring into the ocean off the Big Island and found that it actually created a nutrient-thick soup across a wide expanse of ocean that helped algae to thrive. The nutrients did not come from the lava itself, they found, but because the lava was heating up subsurface water and pushing nutrients deep in the ocean up to the surface. The Pacific Ocean is actually quite nutrient-poor, which makes the algae bloom all the more unique.

Discover Solution 364: Nesting boxes

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