Sediment geochemistry of the Thetis hypersaline anoxic basin (eastern Mediterranean Sea)

• Permanent anoxia in Thetis basin generates specific cycling of trace elements.
• Microbial sulphate reduction in brines and sediments drives trace metal cycles.
• Thetis sediments do not offer reliable analogues to past anoxic basins.

The Thetis basin is a deep hypersaline anoxic basin in the western part of the Mediterranean Ridge (eastern Mediterranean Sea). It is characterised by highly sulphidic NaCl-saturated brine with one of the highest values of salinity reported from similar basins (S ~ 348‰). The strong pycnocline at the seawater–brine interface induces permanent anoxic bottom conditions driving depositional processes and distribution patterns of redox-sensitive metals in the sediments. This work presents a high-resolution dataset of sedimentological, mineralogical and geochemical features and planktonic foraminifera distribution, derived from the exploration of a 52 cm long box-core sampled in the Thetis sediments. Basing on direct comparisons with available data from other hypersaline records and ancient anoxic organic-rich deep-sea records (sapropels and black shales), we aim to explore the potential of these anoxic basins as natural laboratories to better understand the mechanisms driving geochemical patterns in recent/ancient anoxic sediments.