Abstract
The Arabian Gulf (also known as the Persian Gulf; hereafter simply the Gulf) is a shallow, subtropical, semi-enclosed sea that experiences the highest average summer sea surface temperatures (SSTs) in the global ocean. While local marine organisms have adapted to these extreme conditions, interannual temperature fluctuations result in occasional marine heatwaves (MHWs) that trigger mass coral bleaching and other ecological impacts. However, the climatic drivers of this variability remain poorly understood. In this study, we investigate the sources and mechanisms behind extreme summer SSTs in the Gulf. Analyzing a regional eddy-resolving ocean hindcast simulation combined with ERA5 reanalysis data, we find that extreme summer surface temperatures are tightly linked to lower-than-normal surface pressure over the Arabian Peninsula and higher-than-normal surface pressure over Iran and Pakistan. These pressure anomalies are typically associated with stronger monsoonal winds in the western Arabian Sea and weakened local winds. Enhanced monsoon circulation leads to (i) increased evaporation over the Arabian Sea and greater moisture transport into the Gulf in the lower troposphere, trapping heat near the surface, and (ii) enhanced subsidence over the Arabian Peninsula and the Gulf in the upper troposphere, inducing further surface heat retention. Meanwhile, weakened local Shamal winds – particularly in the northern Gulf – reduce evaporative cooling and facilitate the accumulation of moist, warm air, amplifying local warming. These regional atmospheric changes are strongly modulated by large-scale climate variability modes, with El Niño–Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) together explaining over 50 % of the observed interannual SST variability in the Gulf. La Niña (El Niño) and the negative (positive) phase of the NAO both favor weaker (stronger) Shamal winds and warmer (cooler) SSTs during the peak summer months over the Gulf. Additionally, La Niña (El Niño) is associated with stronger (weaker) monsoon winds in the southern and western Arabian Sea, leading to stronger and more persistent warming (cooling) anomalies in the Gulf. The influence of these teleconnections is additive, with the warmest summers occurring when La Niña and negative NAO phases coincide. These findings have implications for the predictability of summer MHWs and associated ecosystem risks in the Gulf.