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Transient Enhancement and Decoupling of Carbon and Opal Export in Cyclonic Eddies
Author(s) -
Zhou Kuanbo,
Dai Minhan,
Xiu Peng,
Wang Lei,
Hu Jianyu,
BenitezNelson Claudia R.
Publication year - 2020
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2020jc016372
Subject(s) - eddy , biogeochemical cycle , eddy covariance , decoupling (probability) , flux (metallurgy) , atmospheric sciences , settling , oceanography , environmental science , phytoplankton , geology , chemistry , ecosystem , physics , nutrient , meteorology , environmental chemistry , ecology , biology , turbulence , control engineering , engineering , organic chemistry , environmental engineering
Given their ephemeral nature, eddies have proven difficult to study, with contrary results from field observations that typically sample at the center during a specific stage of an eddy lifespan. Using the natural occurring radionuclide 234 Th, we examined particle fluxes within two cyclonic eddies (CEs) at different evolutionary stages (mature stage eddy, C2, and a decay stage eddy, C1) in the oligotrophic western South China Sea (SCS). Using a 1‐D steady state model, 234 Th derived particulate organic carbon (POC) and opal fluxes at 100 m were determined. Both POC and opal fluxes were significantly higher at the eddy edges relative to the eddy cores, with integrated eddy POC and opal fluxes of 6.2 (2.1) mmol C m −2 day −1 and 1.5 (0.28) mmol Si m −2 day −1 in C2 (C1). When compared to non‐eddy regimes, both POC (by 2.6‐fold) and opal fluxes (by 7.5‐fold) in C2 were enhanced; they were reduced and decoupled (0.9‐fold and 1.4‐fold) in C1. The difference in enhancement of particle fluxes and the coupling/decoupling between POC and opal flux likely reflects changes in phytoplankton community structures resulting from eddy evolution. Scaling these results to the entire SCS basin suggests that CEs contribute <4% of the net POC flux but >15% of the opal flux. Therefore, CEs may regulate the biogeochemical cycling of silica to a much greater extent than carbon in the ocean.