The problem with studies...

You Can't Judge an Alga by its Color | Science Blog

These sort of problems are the biggest problems for figuring out things like Global Warming. The people that write the reports assume that they have perfect data. They assume that everything is pretty simple. The problem is that it is EXTREMELY complex. The lack of iron in some algae leads to them being more green than they are supposed to be. Scientists miss 1-2 billion tons of CO2 per year. (one side note, isn't that a big range? you have the top end double the low end!) . Each bit of data needs to be analyzed down to this level, and I don't know that that is possible. This doesn't even cover how the models are made or what assumptions they make. The data that is generated is not always the truth, as assumptions were made. In this case, they assumed that the algae are homogeneous in their growth rate as a function of color in all of the oceans. This is clearly not the case as growth rate is effected by environmental factors.