Hydrographic transformation of the Persian/Arabian Gulf outflow over rough shelf bathymetry in the Gulf of Oman

Hypersaline overflows from marginal seas contribute to global ocean circulation and climate variability. The Persian/Arabian Gulf (P/AG) contributes dense, saline, oxygenated deep outflow into the Arabian Sea's Oxygen Minimum Zone (OMZ). Here, we present high-resolution hydrographic mapping of the United Arab Emirates-Oman margin in the northwestern Arabian Sea, integrating conductivity-temperature-depth profiles, multibeam bathymetry and remotely-operated vehicle imagery. The P/AG outflow forms a thin (10–30 m) bottom-attached layer that, on crossing an abrupt bathymetric step, undergoes a hydraulic transition and thickens to 200 m over the rough, irregular seafloor of the unstable shelf, where dilution and loss of bottom contact occur. Near-bottom salinity, oxygen, and pH decrease systematically downstream in association with enhanced mixing. Distinct benthic assemblages coincide with attached versus detached flow sectors, consistent with differing near-bed hydrodynamic regimes. These observations indicate that the bathymetric step/hydraulic transition is responsible for the near-field plume transformation followed by the lower effect of bathymetric roughness. Because outflow density depends on Gulf warming and evaporation, modest climatic shifts may alter outflow dynamics, its detachment depth, pathway geometry, and intermediate-depth ventilation of the Arabian Sea OMZ.