Arctic Carbon Pump Stalls as Sea Ice Stabilises

The Arctic Ocean has warmed rapidly in recent decades, leading to a stark decline in sea ice. Scientists have long debated how this loss affects the 'biological pump'—the vital mechanism by which marine organisms, such as phytoplankton, capture carbon from the atmosphere and transport it to the deep ocean for long-term storage. A new study utilising satellite data from 2003 to 2022 has identified a distinct 'regime shift' in this process.

Initially, the results seemed promising. Between 2003 and 2012, as sea ice retreated, the biological pump became significantly stronger and more efficient. However, this positive trend did not last. From 2013 to 2022, the pump's efficiency plateaued, coinciding with a period of stabilised sea ice conditions and an increase in overall phytoplankton biomass.

Looking to the future, Earth system model simulations spanning from 1850 to 2100 support the link between ice loss and pump behaviour but offer a sombre prediction. The models project that under nearly ice-free conditions, the biological pump will actually weaken. This potential collapse is associated with shifts in the community structure of phytoplankton—the microscopic plants at the base of the food web. These findings underscore a critical vulnerability: the Arctic's capacity to sequester carbon is far from guaranteed as the climate continues to change.