Southern Ocean trace gas experiment shows deep water mixing is slow, with implications for carbon storage

Scientists behind the DIMES experiment released a trace gas into the Southern Ocean and tracked it for years to measure how slowly deep water mixes across density layers. The Southern Ocean is a key route for moving heat, nutrients, and carbon between the surface and the deep sea, so the mixing rate matters for understanding how much carbon the ocean can absorb and hold. The results show that vertical mixing is slower than many models assumed. That means water masses that take up carbon dioxide at the surface may stay isolated from the deep ocean for longer, which changes how we estimate the ocean's capacity to store carbon over decades to centuries. For people working on carbon accounting or climate policy, the finding is a reminder that ocean carbon uptake is not a simple sink. The timing and physical pathways matter when projecting how much CO2 the ocean will keep out of the atmosphere.