Back of Envelope Calculations
Here are some "back of an envelope" calculations to put the ideas presented above into a global perspective.
The calculations on Carbon Sequestration were based on WOCE data for the East Pacific where there is a large amount of nitrate and phosphate present at depth in the ocean. Using WOCE sections P18 and P21 it turns out that the nitrate bearing waters extend 5000 km N-S, 7000 km E-W and have a depth range of 1500m giving the total volume of the nitrate bearing waters of 5 x 10^16 m3. The average concentration of nitrate is about 35 µMol / kg which leads to a total mass of nitrate of 114 Pg (1 Pg = 10^15 g, pronounced "petagram").
For tropical waters at about 21 degC, carbon is removed from the atmosphere at about the same molar rate as the nitrate brought up by the Nutrient Megapump. Hence that East Pacific nitrate mass has the potential to remove about the same amount of CO2 from the atmosphere, i.e. about 100 Pg. The total amount of CO2 in the atmosphere is around 700 Pg which means that the East Pacific nitrate mass has the potential to reduce atmospheric carbon by about 14 percent.
And that is using only one part of one ocean! Using other nitrate masses in other parts of the ocean we could perhaps remove all of the atmospheric CO2 and trigger another ice-age.
There is very little likelihood of that happening however. The Nutrient Megapump brings up 220 m3/s which is 7.3 X 10^9 m3/year. Using the total volume calculated above it would take 5 x 10^16 / 7.3 X 10^9 or about 7 million years for total CO2 removal to happen using a single Nutrient Megapump. Even with 1000 Nutrient Megapumps it would still take 7000 years. So there will be plenty of time to study consequences and to take corrective action.
So there is no need to worry about ice-ages as an unintended consequence of deploying Nutrient Megapumps.
The "Tampering" Argument
One of the most persistent arguments voiced against the Nutrient Megapump is the idea that we are "tampering with Nature". This is not a scientific argument, it is a religious one. It requires an answer nevertheless.
Every time someone ploughs a field or undergoes a triple bypass procedure, they are tampering with Nature. Mankind has always been tampering with Nature, most profoundly since the invention of firestick farming and agriculture. It is now happening to such a degree that people are genuinely worried about the consequences . . . So why don't our critics want us to "tamper" Nature back to how it was, or to how they think it "should be"?
The answer lies in the intent. Instead of planetary scale effects happening by accident as it were, we intend to deliberately change the planet by an effort of human will. This modern sentiment still arouses humanity's deepest fears about "hubris" and confronting the gods, as it has in the past. It would remind many of Nietzsche and the Nazis. But history shows that it is societies that overcome these fears and get on with it, in this case nutrient mega-pumping, who will ultimately be the most successful biologically. The rest will remain trapped in their superstitions.
It has always been this way when any new machine has come along; when there is a quantum leap in technology rather than a steady evolution. These fears are soon forgotten as people get used to the new machines and practices and find that their benefits outweigh their shortcomings. Hence our no longer requiring motor vehicles to be preceded by a man displaying a red flag.
Furthermore, the construction and deployment of Nutrient Megapumps would not be a sudden process. As more and more of them come online, scientists will be watching for environmental impacts, not because of some law that requires an EIS to be carried out, but because the effectiveness of the Nutrient Megapump as a money maker will be at stake. As problems crop up they will be fixed, just as they were in every other new technology. The megapump will be a boon for oceanographers and marine biologists.
Ocean acidification, excessive atmospheric CO2, diminished marine ecosystems and depleted fisheries are not the only problems that will be fixed by the Nutrient Megapump. Even seafloor HydroThermal Vent (HTV) ecosystems would benefit, via generous Environmental Flows:
Nutrient Megapumps have many economies of scale, so will generally be huge. They will thus generally harness only most energetic 1-10 Giga-Watt (GW, 10^9W) HTVs, such as the 1.7 GW TAG field in the mid-North Atlantic. Such HTVs are too powerful for much nearby life, but powerful enough to allow richer than natural, HTV ecosystem gardens fed by environmental flows, surrounding seafloor bases of Nutrient Megapumps. Such gardens could be accessible to researchers and others, for viewing and so on, say via a lift from the surface tower.
Hunter-Gatherers and Farmers
If this project is successful, and Nutrient Megapumps start to be deployed in ever larger numbers, it will represent a sociological shift similar to the invention of agriculture. As it stands now, fishing is still an activity of hunter-gatherers. Only nowadays the hunters have GPS and depth sounders and vessels that stay at sea for a year at a time with nets as big as skyscrapers. There is huge, destructive competition for the resource. It is a classic example of Gareth Hardin's "The Tragedy of the Commons". Despite all the fisheries regulations and all the pious international committees, the rape of the oceans still goes on.
Introducing Nutrient Megapumps into this scenario revolutionizes it and makes fishing the oceans much more like farming. There will be an investment to look after. Over-fishing becomes foolish not merely unfortunate because it depreciates the value of the investment. The legal and political issues discussed in the previous section can and must be overcome.
Using geothermal energy to mix the ocean offers the possibility of the ocean becoming the new prairie, the new steppe.
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