Modern carbonate sedimentation in an extreme marine environment: The southeastern Arabian Gulf

AbstractWe report salinity and temperature of seawater of the southeastern Arabian Gulf from CTD surveys in August 2024 and March 2025. Uniformly high temperatures exceeding 34 °C in August 2024 down to 30 m water depth and extending up to 80 km offshore have been recorded. Seasonal salinity variations show the effect of cyclonal circulation on the southeastern Gulf and high rates of evaporation, which are also evident in δ18O values of seawater that show a trend with salinity similar to the Red Sea. Sediment cores retrieved along a 115 km long onshore-offshore transect down to 52 m of water depth consist predominantly of medium to fine sand deposited above the effective wave base. Micro-mollusks and benthic foraminifers are the major benthic and nannoplankton and pteropods are the major planktonic sediment producers. According to their oxygen isotopic composition, bivalve shells form predominantly during the warm season, while calcareous nannoplankton appears to precipitate calcite during the cooler season. Carbonate production of the southeastern Gulf is compared with previously published geochemical evidence, and the depositional system of a carbonate ramp is critically discussed. Monitoring of seawater properties and more detailed studies of the major benthic and planktonic carbonate producers are required to understand diversity patterns in relation to the extreme environmental conditions and predicted climate change.