Changjiang sediment discharge to the East China Sea at the time scale of months to years

The riverine derived particles play significant roles in sedimentological and geomorphological processes as well as biogeochemical cycles in estuaries. We collected a suite of water and sediment samples from the Changjiang (Yangtze) Estuary and adjacent East China Sea during to observe variations in the particulate ²³⁴Th, ⁷Be, ²¹⁰Pb, and ¹³⁷Cs activities as well as in particle transport, deposition, and resuspension. In the Changjiang Estuary, sedimentary particles in the North Passage experienced net deposition during neap tides whereas those in more seaward areas of the North Passage exhibited net resuspension during spring tides. based on a two-dimensional model of ⁷Be, ²³⁴Th, and ²¹⁰Pb. Using ⁷Be/²¹⁰Pb_ex and ¹³⁷Cs/²¹⁰Pb_ex activity ratios as tracers, we deduced that most of particles in the North Passage were not derived from the direct deposition of Changjiang input particles but were transported there from sediment deposited offshore. These riverine particles would undergo 3-6 years multiple cycles of deposition-resuspension-transport-deposition-resuspension before eventually buried in the shelf or export from inner shelf. The ⁷Be/²¹⁰Pb_ex ratio indicates a southward transport pathway in spring and northeastward transport pathway in summer. Besides, ²¹⁰Pb budget in the inner shelf of the ECS show that a small fraction (at most 14% of annual Changjiang sediment discharge in 2011) of particles could be transported offshore. The ratio of the mobile mud inventory of ²³⁴Th_ex/production in the overlying water column of > 2.5 in south inshore indicates that the sediment focusing resulted in the increased mass flux.