Floating Oases of Sinking Carbon

While reading Lovelock back in March - The Revenge of Gaia - one area he talks about got me thinking.

He states that the ocean surface layers, when they are hotter than 10 degrees C, are largely unmixed with the nutirent-rich lower layers, and so microscopic life is virtually absent - vast areas of ocean are barren unless storms or coastal run-off changes the situation.

Thus when the ice ages retreat, and the planet warms during an interglacial, the area of ocean that contributes to carbon sequestration is reduced.

Now that we are heating the planet beyond the interglacial maximum, the cool areas of ocean are shrinking further, and limited to regions with restricted sunlight. As a result, the loss of algae is exacerbating global warming.

Two things occured to me.

1. We should be grateful for more hurricanes as it promotes microbial lifespans in the tropical oceans.
2. There must be a way to pump nutirent-rich water to the surface and create oases of life that sequester carbon and (in theory at least) generate cloud-cover that cools the planet.

So another thought-invention:
A weighted tube, manufactured as cheaply as possible.
The heat difference between the bottom and top is used to drive a motor.
The motor drives a pump, which pumps cold water up from 200 meters below the sea surface to the top.
The cold nutrient-rich water feeds algae all year round as it floats around the oceans.

Drop a few billion of them into the oceans and we can cool the planet down again.

Variants - as pumping water takes a lot of energy, the heat difference might not be enough.

• Instead, the wave energy at the top might be harnessed to drive a pump, as the bulk of the machine will be below the waves and can be made to stay static relative to them.
• Alternatively, tether them to the sea bed (where it is shallow enough) and mount a wind turbine on top to drive the pumps.
• Pump air downwards to bubble up and create an upwelling current. Has the added benefit that some of the air will dissolve in the water.

I found out a couple of days later that a scientist has already studied a similar concept and published his paper here. This uses a fixed coastal installation, but if a small, self-propelled unit can be manufactured cheaply enough, then they can be used to 'buy' carbon credits and will pay for themselves.

As always, comments and criticisms welcomed.