Enhanced organic carbon fluxes at mesoscale eddies near the Kuroshio

Mesoscale eddies in the subtropical oligotrophic ocean are ubiquitous and play an important role in nutrient supply and oceanic primary production. However, it is still unclear whether these mesoscale eddies can efficiently transfer carbon dioxide from the atmosphere to deep waters via biological pump because of their transient nature. In 2007, particulate organic carbon (POC) fluxes, measured below the euphotic zone at the edge of warm eddy near the Kuroshio were 136–194 mg-C m⁻² d⁻¹ which was greatly elevated over that (average POC flux = 30 mg-C m⁻² d⁻¹) determined in the nutrient-depleted oligotrophic waters in the Western North Pacific (WNP). In 2010, higher POC fluxes (83–115 mg-C m⁻² d⁻¹) were also observed at the boundary of mesoscale eddies in the WNP. The enhanced POC flux at the edge of eddies was mainly attributed to both large denuded diatom frustules and zooplankton fecal pellets according to scanning electron microscopy (SEM) examination. The result reveals that mesoscale eddies in the warm subtropical water can efficiently increase biological activities and the oceanic carbon export flux.