oa Tidal Oscillations Pump the Seaward Transfer of Terrestrial Organic Matter Deposited in the Estuary

Tidal oscillations, as one of major driving forces in large river-dominated estuaries, severely alter hydrologic and sedimentary environments of estuaries. Although it can be expected that tidal oscillations do impact the seaward transfer of deposited terrestrial organic matter (tOM) throughout estuaries, it is difficult to be on-site evidenced. In this study, seaward cross-section and sample suits over the tidal cycle in the Yangtze River estuary were designed to probe tidal constraints on tOM export using molecular chemistry of dissolved organic matter (DOM) as a bridge. Results reveal that high abundance of heteroatomic molecules in DOM pool of tidal samples and the occurrence of molecules different from those in the river samples could be indicative of DOM released from sedimentary tOM. While CRAMs or common molecules between the muddy and coastal zone samples further demonstrate the seaward transport of some refractory DOM from previously deposited tOM within estuaries. This study suggests that DOM compositions at the molecular level can be a powerful tool to trace the transfer of sedimentary tOM along the river-estuary-coast continuum, and tidal oscillations play an important role in respect to sedimentary tOM export to the ocean and much more attention must be caused in the future.