There's little point getting too distracted with talk on how to reduce human CO2 emissions until we have succeeded in reversing the Arctic sea-ice crash.
However, as geoengineering for this will be an ongoing annual commitment until CO2 is back in the region of 280ppm, we do need a plan to pump carbon out of the atmosphere and the sea (where 60% of the 500 Gton total human contribution is residing.)
Current estimates are 56.4 billion tonnes C/yr (53.8%), for terrestrial primary production, and 48.5 billion tonnes C/yr for oceanic primary production.
It's been learned that the primary ocean production has fallen by nearly half in the last 100 years. The reduction in windblown dust from irrigation and cultivation of arid areas and the prolonging of the growing season of grasses in arid areas by CO2 increases is most likely the biggest cause of this. This has resulted in the amount of natural wind-borne iron-carrying dust falling dramatically, 30% over the past 30 years alone.
- Tropical rainforests have globally 8 million square km with biomass productivity of 2000g Carbon per square meter for a total of 16 Gtons of Carbon per year. Doubling this area would only get near an extra 16 Gtons of annual carbon pulldown after 1 to 2 decades and with studies showing drought stress already turning Amazon and stheast Asian rainforests now net CO2 producers rather than removers no gains might occur at all.
- Temperate forests have globally 19 million square km with biomass productivity of 1,250g Carbon per square meter for a total of 24 Gtons of Carbon per year. Doubling this area would only get near an extra 24 Gtons of annual carbon pulldown after 1 to 2 decades, and then would need a further 20 years to remove the 500 Gton existing carbon debt, and thats assuming that 100 percent of carbon taken in by these trees can be kept away from consumers and decomposers.
- The Oceans have globally 350 million square km with average biomass productivity of 140 gC/m²/yr for a total of 48.5 Gtons of Carbon per year. This is heavily weighted towards coastal areas at present. The open Oceans are 311 million sqkm with average biomass productivity of 125 gC/m²/yr and a total of 39 Gtons of Carbon per year, however, as can be clearly seen on the map below, some 80% of the ocean are so isolated from land sourced nutrient inputs that their productivity is about 1/100 of the most productive oceanic zones.
|map of the earth showing primary (photosynthetic) productivity, from: http://upload.wikimedia.org/wikipedia/commons/4/44/Seawifs_global_biosphere.jpg|
Oceanic desolate zone at 80% of 311 million sqkm is 249 million sqkm. 50 GtonsC/249million = 201 tonsC per sqkm per year = 200g C per sqmeter per year average. With prime coastal Aquatic enviroment like estuarys and coral reefs producing 10x that at 2000+ gC/sqm it would seem very achievable to increase the deep ocean productivity this much.
Doubling the productivity of the oceans could pump down the global 500 Gton Carbon burden in as little as 10 years and is possible, affordable, already very well studied.
In the currently near sterile central oceans the absence of an existing foodchain would ensure most of this Phytoplankton Carbon will die and sink a couple of hundred meters into the tidal mixed layer.
This can be a problem....
The amount of organic carbon needed to completely remove all oxygen from the WHOLE ocean as it is decomposed by bacteria is thought to be 1000 Gton C. Just letting the phytoplankton sink into the tidal mixed zone, which is low in oxygen already, would be a very bad idea. Back to this later.
As can be seen on the front page graphic of: http://www.aslo.org/meetings/Phytoplankton_Production_Symposium_Report.pdf
The benefits of iron fertilization alone are only achievable in the Nutrient Rich Iron Depleted zones of the southern ocean to 35degr sth, the equatorial oceans to 20degr sth and 10degr nth, and the nth pacific from 40 degr nth. These areas can easily be stimulated urgently.
At the low figure of 1 million tonC/1ton Fe we would annualy need 50GtC/1MtC= 50000 tons of iron dust -bugger all.
Antarctic krill have a total fresh biomass of up to 500 million tons. This will increase several times over when we iron fert the southern ocean.
The rest of the desolate zones need nitrogen and phosphorus. Rather than using mined phosphates and CO2 producing urea for nitrogen there are these alternatives:
- Natural volcanic ash. There are concerns about heavy metal contamination from this but as long as we stick to siliceous ash from recycled seafloor volcanism we should be pretty OK.
- Wave pumped chimneys. Tested already, these pump nutrient rich deep benthic water via wave power. We would however need millions of these due to scale limitations imposed by ocean wavelengths.
- Chimneys driven by submarine volcanism. An idea I was looking at 10 yrs ago (dibs on the carbon credits, giggles, could make me a trillionaire) this could quickly fill the oceanic gyres of the desolate zones with all the deep benthic and volcano enriched nutrients needed.
- Good old fashioned blood and bone. Puree krill from the southern ocean and fert the low nutrient desolate zones.
Simultaneous with fertilising the desolate zones we'll need to seed them with the best diatoms and suitable higher temp krill species such as north pacific, common in the sea of Japan. It would be possible to multiply world krill population 100x, to the region of 50 Gtons, making them the biggest living carbon store on the planet
Krill are looking very good for Ocean Fertilization for a number of reasons:
a) Getting phytoplankton produced carbon to seafloor or depth.
- Approximately every 13 to 20 days, krill shed their chitinous exoskeleton which is rich in stable CaCO3.
- Krill are very untidy feeders, and often spit out aggregates of phytoplankton (spit balls) containing thousands of cells sticking together.
- They produce fecal strings that still contain significant amounts of carbon and the carbonate/silica glass shells of the diatoms.
These are all heavy and sink very fast into the deep benthic zone and ocean floor. Oxygen levels are higher down there, and the deep benthic zone is much larger in volume than the rest of the worlds oceans. Besides which, unlike Phytoplankton alone, the spitballs and fecal strings stand a much beter chance of not being decomposed and using up oyxgen. The exoskeletons won't be decomposed at all.
Quote wikipedia: "If the phytoplankton is consumed by other [than krill] components of the pelagic ecosystem, most of the carbon remains in the upper strata. There is speculation that this process is one of the largest biofeedback mechanisms of the planet, maybe the most sizable of all, driven by a gigantic biomass"
b) They can be dried and pressed for krill oil. Krill oil can be used directly for biodiesel or as food suppliments.
c) Dried krill (pressed or not),( and any other biomass) can be pyrolysised for gas, pyrolysis oil for existing power plants, and these can have their flue CO2 fed into algae ponds for negative carbon energy.
- The pyrolysis oil can be used directly for large diesels like ships and heavy machinery.
- The water soluble portion of pyrolysis oil can be used for timber construction adhesive for plywoods, chipboards, and laminated beams etc
- Existing refineries can produce bio-petrols, bio-diesels, and bio-plastics from pyrolysis oil with little modification.
- Pyrolysis also produces biochar, which is terrific fertiliser. Producing soils called Terra Preta that are able to sequester fresh carbon from humus, water and nutrients better than any other soils on the planet, and holding fertility for thousands of years. This is the best and safest way to bury carbon.
e) Krill are the best food for a large number of fish and whale species. Putting carbon into living marine biomass is a safe store, and replacing the carbon that we have lost by depleting those stocks.
f) Krill are very efficient phytoplankton harvesters, sometimes reaching densities of 10,000–30,000 individual animals per cubic metre. They quickly swarm to any plankton bloom in the area.
Using them to harvest phytoplankton, and then using simple krill nets on the worlds fishing fleet, is much easier than getting phytoplankton out of the ocean ourselves, as that requires energy intensive centrifuge separation of large quantities of water.
g) Krill Females lay 6,000–10,000 eggs at one time, and they reach maturity after 2-3 years.
- Obviously they can quickly build biomass to any level we can provide food for. Particularly if we are putting them in fresh habitat where small fish that normally consume lots of tiny immature krill are absent.
If we increased the total biomass of krill to 50 Gton fresh biomass as suggested above, that would be about 10 Gton C, then we could remove this amount of Carbon from the ocean every 2 years, this alone has the potential to remove 100 Gton C from the ocean/atmosphere in twenty years.
As krill are such messy feeders, inefficient digesters and shed carbonate rich exoskeletons every 2-3 weeks, they probably would sink to the ocean floor to relatively safely aggregate into sediments, stable carbonate and undecomposed organic carbon around 100 times as much as that. So burying 500Gton C of CO2 in one year would be possible.
Obviously we only need to increase Krill populations by 10x to get the result we need in about 10 years total including the breed up time.
We'd be best to harvest as much as possible to refertilise and replace the carbon in our soils. Remember that about 600 Gton C of carbon from our soils has gone into the oceans already in the last 2000 years.