Mesoscale ocean fronts enhance carbon export due to gravitational sinking and subduction.
basic_science · Level V
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- Record sourced from PubMed, PMID 28115723.
- Also identified by DOI 10.1073/pnas.1609435114 and PMC identifier 5307443.
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Abstract
Enhanced vertical carbon transport (gravitational sinking and subduction) at mesoscale ocean fronts may explain the demonstrated imbalance of new production and sinking particle export in coastal upwelling ecosystems. Based on flux assessments from <sup>238</sup>U:<sup>234</sup>Th disequilibrium and sediment traps, we found 2 to 3 times higher rates of gravitational particle export near a deep-water front (305 mg C⋅m<sup>-2</sup>⋅d<sup>-1</sup>) compared with adjacent water or to mean (nonfrontal) regional conditions. Elevated particle flux at the front was mechanistically linked to Fe-stressed diatoms and high mesozooplankton fecal pellet production. Using a data assimilative regional ocean model fit to measured conditions, we estimate that an additional ∼225 mg C⋅m<sup>-2</sup>⋅d<sup>-1</sup> was exported as subduction of particle-rich water at the front, highlighting a transport mechanism that is not captured by sediment traps and is poorly quantified by most models and in situ measurements. Mesoscale fronts may be responsible for over a quarter of total organic carbon sequestration in the California Current and other coastal upwelling ecosystems.