ABOARD THE AKADEMIK IOFFE, Drake Passage — Located at the southern confluence of the Atlantic and Pacific oceans, the Drake Passage is infamous for its gargantuan waves, powerful winds and intense storms, as well as its place in history. But perhaps equally intriguing is its potential as a venue for a massive geoengineering experiment.The Southern Ocean, which includes the majority of the Drake, is high in nutrients, but low in chlorophyll — an indicator of biological activity. While there are plenty of nutrients like nitrogen and phosphorous in the water column, a relative lack of other nutrients is likely limiting planktonic growth. The primary suspect for the missing ingredient is iron, which makes the area a tempting place to experiment with iron-seeding to stimulate biological activity that would soak up atmospheric carbon dioxide, and potentially help mitigate climate change.But there are also clear dangers in tinkering with poorly understood global systems. "There is no control experiment for a large scale perturbation of the Earth," said MIT engineer Janelle Thompson. "At what point does a scientific experiment become geoengineering?"