The aim of this work was to document the seasonal and inter-annual dynamic of dissolved oxygen and ancillary data (T, S, Chl-a, turbidity, pH) along a cross-shelf transect off the Gironde estuary. This work has been motivated by recent simulations that suggest the occurrence of seasonal bottom deoxygenations in this River-dominated Ocean Margin (Riomar); but unfortunately there were no data sets to test this hypothesis until now. Profiles of temperature, salinity and dissolved oxygen were performed in the water column of the West Gironde Mud Patch off the Gironde estuary (from 45°46.383’N – 1°28.925’W to 45°35.524’N - 1°50.689’W) during seven cruises on the R/V Côte de la Manche (doi: 10.18142/284 ; 10.17600/18000861) between 2016 and 2021 (October 2016, August 2017, January 2018, April 2018, July 2019, April 2021, October 2021). Turbidity was measured in January and April 2018, July 2019 and October 2021, Chl-a in October 2016, August 2017, January 2018, April 2018 and July 2019 and pH in October 2021. This dataset had permitted to validate the occurrence of bottom deoxygenations when the water column is stratified.

In the context of EMPHASE project (ANR-FRQ), two fields campaigns were carried out to determine the settling velocity and properties of suspended sediments during a semi-diurnal tidal cycle, as well as hydrodynamic conditions and water properties. The two sampling stations Bordeaux (Garonne Tidal River) and Fort Medoc (Gironde EStuary) were representative of two regions: a tidal river dominated by fresh water and an estuary affected by salty or brackish waters, inside the same land-sea continuum. Quasi in-situ measurements of settling velocity were carried out with a recently-patented instrument named System for the Characterisation of Aggregates and Flocs (SCAF).