Growing seaweed to capture carbon dioxide could deplete ocean nutrients and reduce the effectiveness of natural carbon sinks, according to new research. The approach risks increasing atmospheric CO2 in some scenarios rather than lowering it. Two studies highlight significant ecological trade-offs.
Researchers modeled large-scale seaweed cultivation across coastal waters. They found that growing 20 billion tonnes annually would deplete nitrogen, phosphorus and iron, cutting seaweed growth by 95 percent after 25 years while reducing global phytoplankton by up to 8 percent.
Manon Berger at the University of Bern said the technique “could backfire locally” and that “the potential is extremely limited, with large ecological consequences.” Suitable areas without harming phytoplankton cover just 0.05 percent of the ocean.
A separate study examined iron fertilization to boost growth. It showed potential removal of up to 40 billion tonnes of CO2 yearly but would halve ocean plankton, harming marine food chains. Andrew Yool of the UK National Oceanography Centre noted the process would transfer nutrients to depth and “strangle the natural ecosystem.”