Friday, June 22, 2007

Eating their way to carbon neutrality

At work we got to talking about the incredible size of blue whales. The relevant stats are at

At the bottom of this document it talks about how much krill these things would have eaten. Krill live at the surface, perhaps 1 meter, so 15 billion cubic meters of ocean is something like 15000 square kilometers, which is the area of maximally krill-swarmed antartic water that the blue whale population would have filtered through each year, before we killed nearly all of them. I don't know how fast krill populations reproduce, but it seems like that's enough consumption to materially affect the local environment.

Compare 136 million metric tons of krill per year eaten by all those whales (blue, fin, humpback and sei) to about 700 million metric tons of oil a year consumed by the United States. Obviously krill don't have quite the energy content of crude oil, but the notion that the numbers are even comparable is just boggling.

The document suggests that krill have energy content of 3.8 MJ/kg, which is considerably lower than the approximately 25 MJ/kg of crude oil. Each day a blue whale would eat 3 tons of krill and gain 400 kg, so if the weight gain was mostly fat and not water, the whales would have to be converting nearly all the swallowed krill energy into fat. Later that would be burned off into CO2, so my guess is that these whales were gigantic hydrocarbon burners, consuming energy equivalent to 3% of U.S. oil consumption.

Almost all those animals are gone now, so I wonder what is happening to all those krill down near Antartica right now. Nature abhors a vacuum.

Thursday, June 07, 2007

Fertilizing the ocean with iron

John Martin suggested seeding the South Pacific with iron ("The Iron Hypothesis") to increase the photosynthetic activity there. (Here's a clip of Richard Barber describing the idea.) If this increase is to sequester CO2, some of the carbon fixed from the atmosphere has to fall into the deep ocean rather than being respired by animals. Generally, live animals don't fall into the deep ocean, but excrement (referred to as "marine snow") does. So far as I know, nobody knows the carbon content or overall rate of this marine snow, and certainly nobody has any idea how it might change if you dumped a bunch of iron into the water.

One thing is clear though: dump iron into any of a number of spots in the ocean and you get a massive increase in biological activity. More phytoplankton, more zooplankton, and according to one report, more larger fish from surrounding areas swarming in to eat the bounty. This makes sense to me: these productivity spikes have probably been happening for millions of years from dust storms. Fish can probably smell the extra nutrients or some other related effect, and I'm sure the effect is like a temporary oasis in a desert.

What is less clear, but certainly possible, is that the increase in productivity at the base of the food chain leads to an increase farther up. That's interesting to me because I don't eat a lot of zooplankton myself, but I do enjoy tuna, salmon, and a number of other pelagic fish which are all under pressure from commercial fishing. I'd certainly support my tax dollars going to a study to find if iron seeding increased the productivity of a fishery. If it did, you'd think the commercial fishermen would be more than willing to take some iron fertilizer out with them on each trip.

Fishery fertilization might significantly improve the global human food supply, both in quantity and quality. If it works, you'd have fairly wide-scale and sustained fertilization, which would make the carbon sequestration (and other) effects of fertilization much easier to study. After a decade or two of that, you might have enough information to know whether more massive fertilization might help with the global warming problem.