Decoupling between particulate carbon and biogenic silica export within North Pacific Subtropical Gyre cyclonic eddies.

Kuanbo Zhou1, Claudia R Benitez-Nelson2, Jie Huang3, Peng Xiu4, Zhenyu Sun1 and Minhan Dai5, (1)Xiamen University, State Key Laboratory of Marine Environmental Science, Xiamen, China, (2)University of South Carolina, School of the Earth, Ocean, and Environment, Columbia, United States, (3)Tsinghua University, Beijing, China, (4)SCSIO South China Sea Institute of Oceanology, Chinese Acaademy of Sciences, Guangzhou, China, (5)Xiamen Univ, Xiamen, China
Mesoscale eddies may mediate the flux of nutrients into the photic zone and ultimately the magnitude and composition of particle export to depth. In this study, we identified 24 mesoscale cyclonic eddies using satellite altimetry that drifted past Station ALOHA in the North Pacific Subtropical Gyre from 1993-2014. Both carbon and silica fluxes varied significantly within (core versus edge) and between individual eddies depending on season and age. Elevated carbon and silica flux anomalies occurred at eddy edges and during the early stages of the eddy life span for carbon (2-4 weeks) and throughout the entire eddy lifespan for silica. On annual timescales, there was little to no significant enhancement of carbon flux (1.1-1.3-fold) relative to non-eddy and non-bloom periods. In contrast, biogenic silica fluxes were elevated by an average of 247±120% (1.2-3.8-fold) and are comparable to nitrogen fixation induced seasonal export pulses that characterize the ecosystem. Our results confirm that mesoscale features in the North Pacific result in more efficient export of biogenic silica relative to carbon regardless of age or location with the eddy. The decoupling between silica and carbon flux within North Pacific eddies implies that these two critical elements, central to marine food webs, differ in their mechanisms of export to depth such as active sinking and passive subduction, that require further investigation.