Ocean deoxygenation caused non-linear responses in the structure and functioning of benthic ecosystems

The O2 content of the global ocean has been declining progressively over the past decades, mainly because of human activities and global warming. Nevertheless, how long-term deoxygenation affects macrobenthic communities, sediment biogeochemistry and their mutual feedback remains poorly understood. Here, we evaluate the response of the benthic assemblages and biogeochemical functioning to decreasing O2 concentrations along the persistent bottom-water dissolved O2 gradient of the Estuary and Gulf of St. Lawrence (QC, Canada). We report several of non-linear biodiversity and functional responses to decreasing O2 concentrations, and identify an O2 threshold that occurs at approximately at 63 µM. Below this threshold, macrobenthic community assemblages change, and bioturbation rates drastically decrease to near zero. Consequently, the sequence of electron acceptors used to metabolize the sedimentary organic matter is squeezed towards the sediment surface while reduced compounds accumulate c..., Data collected from September 14th to 29th, 2020 on-board the R/V Coriolis II. For more details, please see section 2. Materials and methods in the associated publication., , # Ocean deoxygenation caused non-linear responses in the structure and functioning of benthic ecosystems

[https://doi.org/10.5061/dryad.6djh9w16w](https://doi.org/10.5061/dryad.6djh9w16w)

This dataset includes data from a scientific cruise on board the RV *Coriolis II* along the Lower Estuary and Gulf of St. Lawrence. A gradient of oxygen concentration exist from the gulf and the head of the lower Saint Lawrence estuary and data was collected at different location along this gradient to assess the effect of bottom waters deoxygenation on the functioning of benthic ecosystem.

## Description of the data and file structure

This data set is organized in 23 tabular data files
More information about the sampling procedure and measurement preformed can be found in the method section of the associated publication

### CTD cast data

CTD cast data are included in 11 .cnv files. These files contain continuous profile of data recorded during the down and up cast. Data from the down cast was us...