The ocean’s biological carbon pump may be shuttling less carbon from the surface to the depths than is assumed in most climate models.
Chelsey Baker of the National Oceanography Centre in Southampton, UK, and her colleagues analysed the amount of particulate organic carbon — microscopic detritus from marine life — in samples taken from 144 locations during eight Atlantic Ocean cruises from 2009 to 2013. The results suggest that the bulk of the carbon in the deep ocean is in the form of small particles, partly because larger ones become fragmented in midwater. But smaller particles sink more slowly than large ones and so are more likely to be chemically broken down before they reach the ocean floor, where they can be locked into sediment.
The researchers suggest that biogeochemical models, which assume a larger proportion of big, fast-sinking particles at great depths, might overestimate long-term carbon storage in the ocean.