Investigating the long-term variability of the Red Sea marine heatwaves and their relationship to different climate modes: focus on 2010 events in the northern basin

Abstract. Marine heatwaves (MHWs) have been increasing in frequency, intensity, and duration worldwide, which poses a serious threat to marine ecosystems and fisheries. The Red Sea (RS), a semi-enclosed marginal sea, is highly vulnerable to climate change due to its small volume and slow rate of water renewal. Despite the importance of the RS, MHWs in this region remain poorly studied, and understanding of their spatial and temporal characteristics and forcing mechanisms is limited. This study examines MHWs in the RS over the last 4 decades (1982–2021) and their relationship to large-scale climate modes, with particular focus on the 2010 MHW event in the northern Red Sea (NRS). Analysis of sea surface temperature anomaly (SSTA) trends in the RS revealed a decadal variability, with the highest warming trends occurring alternately in the northern and southern regions. The RS has experienced a significant warming trend over the last 4 decades, which has intensified since 2016. This warming has led to an increase in the frequency and duration of MHWs in the region, with 46 % of events and 58 % of MHW days occurring only in the last decade. The RS exhibits a meridional gradient, with decreasing mean annual MHW intensity and duration but increasing mean annual MHW frequency from north to south. The annual MHW frequency in the NRS peaked in 2010, 2018, 2019, and 2021, while, in the Southern Red Sea (SRS), the highest frequency occurred in 1998 and from 2017 to 2021. The study also examined the correlation between MHWs and climate indices and found that the Atlantic Multidecadal Oscillation (AMO), the Indian Ocean Dipole (IOD), and the East Atlantic/West Russia pattern (EATL/WRUS) were the three dominant modes that correlated with SSTAs and MHWs in the region. The North Atlantic Oscillation (NAO) and the Oceanic Niño Index (ONI) showed weaker and less significant correlations. Finally, the authors conducted a case study of the 2010 MHW event in the NRS, which was the most intense and longest winter event of the year. Using a high-resolution ocean model and atmospheric reanalysis data, it was found that the MHW in late winter 2010 in the NRS extended to a depth of 120 m and was driven by a combination of atmospheric forcings, particularly an increase in air temperature (Tair) and humidity, possibly linked to reduced winds leading to reduced latent heat flux (LHF) and strong ocean warming, creating favourable conditions for MHWs to occur.