In his letter on ocean thermal energy conversion (OTEC), Graham Cox suggests it could be used to fertilise surface waters with nutrient-rich deep water to promote plankton growth for carbon capture (1 December, p 31).
However, there is a problem. Deep water often contains a lot of dissolved inorganic carbon from sinking organic matter which would be released by the process, and so would greatly reduce, if not eliminate, any benefits.
This was indicated in research by Andrew Yool et al (Journal of Geophysical Research, vol 114, p C08009) and Andreas Oschlies et al (Geophysical Research Letters, vol 37, p L04701).
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