Transport and depositional process of soil organic matter during wet and dry storms on the Têt inner shelf (NW Mediterranean)

River floods and storm waves are major processes for the dispersal and deposition of terrestrial organic matter (OM) in river-dominated coastal areas. A “wet storm” is connected to a flood with a high river discharge, while a “dry storm” is not associated with a flood. To better understand the sedimentation dynamics of terrestrial OM, especially soil OM, at the land–ocean interface during wet and dry storms, we studied sediment trap and core material collected on the Têt inner shelf (NW Mediterranean) using multiple organic proxies in combination with hydrodynamic parameters. The proportion of soil OM to the total OM in the trap material calculated based on the BIT (Branched and Isoprenoid Tetraether) index was higher during both wet (~ 40%) and dry (~ 30%) storms than during non-storm periods (~ 10%). However, only surface sediments (1-cm thick layers) recovered after December wet and moderate storms in 2003 showed enhanced soil OM percentages compared to the deeper sediments deposited during the last century. Given that the wet storm eroded 4-cm of seabed at the study site, flood-induced fresh soil OM was not deposited on the Têt inner shelf during the wet storm. However, the following moderate storm caused resuspension of flood-associated soil OM which was previously trapped nearshore. Accordingly soil OM was transported to the Têt inner shelf and stored there until the dry storm occurred.