Tracking decadal shifts in nutrient regimes and hydrography in the Persian Gulf from 1977 to 2022

This study compares nutrient and hydrographic conditions in the Persian Gulf based on two major surveys: the Atlantis II expedition (1977) and the PGE2201 cruise (2022). It reveals substantial shifts in depth-averaged nutrient concentrations, with a 4.3-fold rise in dissolved inorganic nitrogen (from ∼0.92 to 3.97 μmol/kg), a 1.4-fold decrease in phosphate (from ∼0.36 to 0.24 μmol/kg), and a 1.7-fold increase in silicate (from ∼1.11 to 1.73 μmol/kg) over 45 years. Sea surface temperature in the northern Gulf increased at ∼0.49 °C per decade- significantly higher than the global ocean average-accompanied by reduced oxygen concentration and increased salinity. Limiting nutrient regimes also changed, transitioning from nitrogen-limited in 1977 to mixed nitrogen- and phosphorus-limited in 2022. These shifts likely result from a combination of regional climate variability, anthropogenic inputs, dust deposition, stratification, sediment interactions, and exchange with the Gulf of Oman. The findings highlight the urgent need for sustained monitoring and adaptive management to protect the Persian Gulf's ecological integrity amid intensifying environmental pressures.