The science has come to prominence only within the last five or six years, and most of the details were not available when the convention was signed in 1992.
"We know that the increasing concentration of CO2 [in the air] is making the oceans more acidic," Mr Benn told BBC News.
"It affects marine life, it affects coral, and that in turn could affect the amount of fish in the sea - and a billion people in the world depend on fish for their principal source of protein.
"It doesn't get as much attention as the other problems; it is really important."
In September, the UN-backed study into
The Economics of Ecosystems and Biodiversity
(Teeb) concluded that the widely-endorsed target of trying to stabilise atmospheric concentrations of CO2 or their equivalent to around 450 parts per million (ppm) would prove lethal to much of the world's coral.
Up to one half of the carbon dioxide (CO2) released by burning fossil fuels over the past 200 years has been absorbed by the world's oceans
Absorbed CO2 in seawater (H2O) forms carbonic acid (H2CO3), lowering the water's pH level and making it more acidic
This raises the hydrogen ion concentration in the water, and limits organisms' access to carbonate ions, which are needed to form hard parts
Mr Benn made his speech during the summit's "oceans day" at a meeting organised by Stanford University and Scripps Institution of Oceanography, both based in California.
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