Tracing global biogeochemical cycles and meridional overturning circulation using chromophoric dissolved organic matter

Basin‐scale distributions of light absorption by chromophoric dissolved organic matter (CDOM) are positively correlated (R 2 > 0.8) with apparent oxygen utilization (AOU) within the top kilometer of the Pacific and Indian Oceans. However, a much weaker correspondence is found for the Atlantic (R 2 < 0.05). Strong correlation between CDOM and AOU indicates that CDOM is created as a byproduct of the oxidation of organic matter from sinking particles. The observed meridional‐depth sections of CDOM result from a balance between biogeochemical processes (autochthonous production and solar bleaching) and the meridional overturning circulation. Rapid mixing in the Atlantic dilutes CDOM in the interior and implies that the time scale for CDOM accumulation is greater than ∼50 years. CDOM emerges as a unique tracer for diagnosing changes in biogeochemistry and the overturning circulation, similar to dissolved oxygen, with the additional feature that it can be quantified from satellite observation.