Plenty more fish in the sea (pt. 1)

I’ve arrived at the first stop on my quest, Eazrah’s nearest galactic neighbour, Planet Crooter.

I was greeted warmly by the inhabitants here and have spent a few days speaking with them about the current state of both our planets' climates, and what action is being taken to control them. They told me about a form of geoengineering here called iron fertilization, though many inhabitants claim it is not really geoengineering at all. I’ll explain why later on.

This is the idea:

1. Iron powder is dissolved into the oceans

(The focus is kept on regions of “high-nutrient, low-chlorophyll” (HNLC) surface water. HNLC means there are lots of nutrients necessary for life in the water, but there’s not much chlorophyll – a pigment crucial for phytoplankton and algae to photosynthesize – indicating there’s not much photosynthesis or plant growth going on. As the water is rich in other nutrients, it’s thought that iron (of lack thereof) limits phytoplankton growth.)

2. Influx of iron into the water stimulates tiny organisms – phytoplankton and algae – to grow into colonies (they call it a plankton bloom, see figure 1)

3. The growth of these organisms effectively sucks organic carbon out of the water...

4. ... meaning less carbon can travel from the water back into the atmosphere. There's also a greater capacity for carbon dioxide to dissolve into the ocean from the atmosphere

5. When the phytoplankton and algae die they sink to the ocean floor, trapping carbon on the ocean bed. This part is the carbon sequestration

Figure 1. The natural-coloured top image is a spectacular plankton bloom off Kamchatka. The bottom image shows scientist-estimations of chlorophyll concentrations in this area. Regions of high chlorophyll concentration correspond with densely plankton-populated water. (Images by Robert Simmon and Jesse Allen, based on MODIS data, via NASA)

I'll explain a little more...

Some scientists speculated that a lack of iron was limiting biological activity in HNLC regions. In an early experiment Coale et. al. (1996) tested this out in a HNLC part of the Pacific Ocean. They saw that when iron was dissolved into the water, algae and phytoplankton populations did indeed start to grow. They also saw a significant drawdown of carbon from the surface water, suggesting iron fertilization had potential as a method of carbon sequestration.

Boyd et. al. (2000) then tested out the same thing in the Southern Ocean. They saw that although there was some increase in algae and phytoplankton, they couldn’t prove there was much carbon sequestration occurring. But then in 2009, Pollard et. al. (amongst others) did confirm carbon sequestration as a result of (natural) iron fertilization in the Southern Ocean.


Mixed results really: it seemed like iron fertilization did stimulate plankton growth, but it was unclear whether it would lead to significant carbon sequestration.

Then came the largest-scale “experiment” of iron fertilization. But it wasn’t performed out of scientific endeavour. A businessman, set on earning money from carbon credits, convinced a small marine restoration organisation, Haida Salmon Restoration Corporation (HSRC), to release 100 tonnes of iron sulphate into the north-eastern Pacific Ocean to boost salmon populations. (The idea being that a plankton bloom would boost fish populations, including salmon.)

In terms of salmon, the “experiment” was a success. But from a geoengineering perspective, it seemed there was little carbon sequestration as most of the phytoplankton were eaten by fish before they had a chance to die, sink to the seafloor and lock carbon away.

The move was also controversial with environmentalists here: there are plenty of reasons why anyone using iron to artificially create plankton blooms should be careful. From risking depleting surface-water oxygen, to accidentally encouraging toxic phytoplankton or algae species blooming.


So far I'm not too impressed with iron fertilization. The evidence suggesting it leads to carbon sequestration is weak, but some evidence does exist so I think it deserves more attention. Maybe the benefits of iron fertilization are more significant over a longer time scale? I’ll stay on Planet Crooter a little longer to find out.