Kuroshio‐Derived Anticyclonic Eddies Drive Lateral Transport and Transformation of Oceanic Dissolved Organic Matter Along the Continental Slope of South China Sea

Abstract Propagation of anticyclonic eddies (ACEs) facilitates the lateral transport of dissolved organic matter (DOM). However, the transformation of DOM within ACEs and its regulation of lateral fluxes of dissolved organic carbon (DOC) remain unclear. High‐resolution sectional distribution of DOC and humic‐like fluorescent DOM (FDOM H ) were investigated across a Kuroshio‐derived ACE (K‐ACE) on the slope of northern South China Sea (SCS). A two‐endmember isopycnal mixing model revealed higher Kuroshio water fraction (0.59 ± 0.13) in K‐ACE than non‐eddy region. DOC removal (maximum 6%) was identified in the upper 200 m of K‐ACE. The shallower mixed layer (<50 m) also revealed signals of FDOM H photobleaching (8%–34%). However, the substantial production of FDOMH (36%–43%) happened below the mixed layer (50–250 m). The regression slope between net FDOM H and apparent oxygen utilization in this layer was steeper in K‐ACE than in non‐eddy region and dark oceans, suggesting K‐ACEs had higher microbial‐mediated in situ production efficiency and rate of refractory DOM. This enhancement could be attributed to increased biogenic particle export, more Kuroshio‐derived DOM transport, and higher oxygen utilization rate at warmer condition within K‐ACE. Analysis of 27‐year (1993–2020) daily eddy data revealed that K‐ACE‐induced lateral transport DOC flux to the northern SCS slope (1.8 ± 0.2 Tg C yr −1 ) constitutes half of the external DOC flux via cross‐shelf transport, highlighting the importance of K‐ACEs in connecting carbon cycles between west Pacific and the northern SCS slope and even shelf areas.