Program
 
Special Session 4: Biogeochemical cycling of trace elements in the ocean: GEOTRACES and beyond
 
 
 
Poster
The conservative behavior of Rare earth elements along the salinity gradient in the Changjiang Estuary-East China Sea interface
SS4-05
Huijun He* , Ocean University of China
Jing zhang, Ocean University of China; University of Toyama
Jie Liang, Ocean University of China
Presenter Email: he-hui-jun@163.com
Rare earth elements (REEs) from the estuary play an important role in their geochemical cycles in the ocean, especially in the continental shelf area. As the biggest shelf marginal sea adjacent to the Pacific Ocean, East China Sea receives a huge amount of freshwater from Changjiang River and provides a good ¡°natural experiment site¡± for the study of REEs behavior along estuarine salinity gradient. In this study water samples were collected along salinity gradient in Changjiang estuary in August 2015 for the measurements of REEs, dissolved organic matter (DOC) and suspended particulate matter concentration (SPM). Laboratory experiments were conducted to mimic the mixing between river water and seawater in order to distinguish the REEs behavior differences as a result of estuarine mixing and resultant physicochemical processes. Results show that the behavior of REEs in various salinity ranges of Changjiang estuary are different. In low salinity range (S<2), REEs are significantly removed, due to colloid flocculation. In middle salinity range (223), REEs behaved conservatively. The main factors that influence REEs were analyzed by normalizing REEs data with DOC and SPM. Combining field observation and laboratory experiments, REEs are mainly controlled by DOC and SPM in low salinity areas (S<10), but DOC, anion and water mass in high salinity areas (S>23). Conclusively DOC, SPM, anion and water mass are main factors that influenced dissolved REEs. Furthermore REEs can be used as water mass tracer to investigate complex water mass mixing and boundary exchange in continental shelf, due to their conservative behavior in high salinity ranges.Acknowledgments: This work was supported by National Natural Science Foundation of China (NSFC-41003052; 41276071; 41530965).