5mp Digital Camera: Sealing leaky Southern Ocean carbon pump boosts ice ages

Iron fertilization of the ocean has been proposed as a way to limit climate warming. The additional iron could stimulate plankton to take up carbon from the atmosphere, but this approach is largely considered to be at least impractical, if not impossible. Despite that, some new research shows just how important this basic process was during past ice ages. It probably won’t help us address the future, but it can definitely help us understand the past.

The new research focuses on the Southern Ocean, which hosts some key processes in the global carbon cycle. Deep ocean currents surface near Antarctica (a process called upwelling), bringing with them lots of nutrients and dissolved carbon dioxide. Finally able to equilibrate with the atmosphere, much of that CO₂ is released from storage.

The nutrients that come with it, however, support rich blooms of phytoplankton that take up CO₂ through photosynthesis. When the plankton die or are eaten, some of that carbon sinks to the deep ocean (often by "riding the fecal express") and back into storage. This process is referred to as the biological carbon pump. In these nutrient-rich waters, iron is the limiting ingredient; phytoplankton will grow until they run out of iron, even if plenty of other nutrients remain.