Program
 
General Session 2: Marine & estuarine biogeochemistry
 
 
 
Poster
Hydrological and biogeochemical controls on absorption and fluorescence of dissolved organic matter in the northern South China Sea
GS2-71-S
Chao Wang* , State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen 361005, P. R. China
Presenter Email: marineswang@163.com
Absorption and fluorescence of dissolved organic matter (CDOM and FDOM) were determined in the oligotrophic regime of northern SCS and WPS to assess the impacts of such margin–open ocean interactions and mesoscale processes on the DOM dynamics. DOM in the upper water of northern SCS showed higher absorption and fluorescence intensities, larger molecular weight (MW), lower photodegradation and recent autochthonous contribution (BIX) than the WPS. The isopycnal mixing model results showed that humic-like FDOM in the upper northern SCS were mainly modulated by conservative mixing with the intruded Kuroshio current, while protein-like substances were more affected by in situ biological activities. DOM in the warm eddy-core showed extremely similar optical properties to the Kuroshio, provided a powerful biogeochemical evidence that warm eddy could shed from the Kuroshio bend through the Luzon Strait. Instead, DOM in the cold eddy-core showed higher humic-like FDOM abundance and larger MW than the eddy-edge and other regions in the northern SCS, due to the upwelling of humic-rich deeper water and enhanced primary production inside the eddy. Moreover, cold eddy could capture more sinking particles and finally increase the accumulation of bio-refractory DOM in the dark ocean. The ratio of two humic-like FDOM (peak C:M) rapidly decreased along Kuroshio intrusion into the SCS, dramatically enhanced/ reduced in the warm/cold eddy-core and slightly increased during the remineralization in the deeper layer. Hence, the optical properties of DOM would be good tracers of the impact of hydrological and biogeochemical processes on the DOM dynamics in the ocean.