This study investigates long-term (1955-2022) changes in Sea Surface Temperature (SST) and upper-ocean Heat Content (OHC) in two adjacent but dynamically distinct basins: the semi-enclosed Persian Gulf and the open Gulf of Oman, connected to the Indian Ocean. Understanding heat storage mechanisms in basins with contrasting geometries is critical for regional climate predictions.



Subsurface temperatures were extracted from the NOAA World Ocean Atlas 2023 at 0.25° resolution across seven decadal periods. Due to data continuity, analysis for the Persian Gulf was limited to 1955-2014, while for the Gulf of Oman it extended to 2022. SST data were obtained from the Climatic Research Unit at 1° resolution. OHC was computed for four depth intervals (0-25, 25-50, 50-75, and 75-100 m) using the standard thermodynamic equation, with linear trends estimated by Ordinary Least Squares.



The findings reveal fundamental differences between the two basins. In the Persian Gulf, warming is strongly concentrated in the upper layers. The temperature trend in the 0-25 m layer is +0.052°C yr⁻¹, corresponding to an OHC increase of 1.62 W m⁻² per decade. With increasing depth, the warming rate diminishes rapidly, becoming weak below 75 m. This pattern reflects shallow depth, strong stratification, high evaporation, and limited mixing in this semi-enclosed basin.



In contrast, the Gulf of Oman exhibits vertically coherent warming. Although the surface warming rate (0.024°C yr⁻¹) is half that of the Persian Gulf, positive temperature and OHC trends extend to 100 m depth. Lower temperature variability and high decadal correlations between SST and OHC across all depths indicate effective vertical mixing and strong connectivity with the Indian Ocean.



Spatially, both basins exhibit a south-north OHC gradient, with maximum values in southern offshore regions and minimum values along northern coasts influenced by upwelling. Decadal correlations between SST and OHC in the Persian Gulf are high in upper layers but drop sharply below 75 m (r = 0.34), indicating decoupling of deep layers from surface signals. In the Gulf of Oman, correlations remain high (r > 0.9) throughout the water column.



In conclusion, despite their proximity, these basins follow fundamentally different heat accumulation pathways. The Persian Gulf acts as an amplifier of short-term thermal variability with surface-focused warming, while the Gulf of Oman functions as a long-term heat reservoir with depth-penetrating warming. These differences, rooted in basin geometry and circulation regime, have direct implications for regional climate feedbacks, marine heat extremes, and sensitive ecosystems such as coral reefs. The study underscores the importance of analyzing both SST and OHC to understand ocean-atmosphere climate interactions in southwestern Asia.