Re: Iron is not enough
"I have always undestood that phosphorus in some soluble form was a limiting element."
Sorry, but your understanding is limited. My Ocean Science lecturers universally defined Iron as the usual limiting nutrient, though in areas Phosphorous may also be limiting, or may be the next limiting nutrient once Iron has been supplied. It may also be that you only need to add a little iron for it to not be limiting, and each area needs a tailored cocktail to get the bets results.
Certainly when I was studying this stuff it was established that it worked quite well, but the cost of actually processing and shipping that iron out there off-set most of the carbon sequestration that took place, which rendered the whole effort somewhat pointless.
Of course if suitable seeding material can be sourced as a waste product of some other processing going on anyway, and it doesn't take much carbon to transport it from it's source to the coast (and sail out to sea), then that changes the equation rather dramatically.
Of course care needs to be taken. Just because an area appears relatively barren of life does not mean it is not supporting certain niche species, and using it as a dumping ground to sequester carbon could - in excess - cause major environmental issues if we continuously bloom areas which should naturally be clear water.
Biting the hand that feeds IT
