The interannual variability of the exchange flow between the Red Sea and the Gulf of Aden through the Bab-al-Mandeb strait is examined based on a high-resolution, nonhydrostatic hindcast model simulation covering a 19-year period (1995–2013), using the MITgcm (MIT general circulation model). The model is validated against moored profiles and along-strait cruise observations collected during the period from June 1995 to November 1996 and 19-year sea surface temperature satellite observations. The model well reproduces the properties of the water masses at the strait over a wide range of spatiotemporal scales, including the typical two- and three-layer seasonal patterns and the related intraseasonal-to-interannual cycles. The seasonality of the exchange flow is predominately determined by the time-varying surface winds, with a higher correlation over the Gulf of Aden, reflecting the importance of local Gulf of Aden processes for the exchanges at the strait. The alternation of the two seasonal patterns is driven by a combination of the buoyancy-driven mean circulation with the wind-induced transport. The onset/offset of the two patterns is estimated to take place one-to-two weeks after the respective monsoon-driven wind reversal. Model results indicate that the onset dates and durations of both patterns exhibit a considerable interannual variability. Additionally, the duration of the summer (winter) exchange pattern presents a significant increasing (decreasing) trend of ~1.45 day/year (~1.22 day/year) over the 19-year period. Significant interannual variabilities and trends are observed in terms of the total volume of water, salt mass, and stored heat of the exchanges. Budget analysis of these trends suggests that the duration of the two exchange patterns is more important in determining the interannual variability and the related trends than the intensity of the exchange, or the variations in mean salinity or temperature of the exchanged water masses.

Mesoscale eddies are a dominant feature of the Red Sea circulation, yet their three-dimensional characteristics remain largely unexplored. This hinders our understanding of about eddy-induced transport in the basin. This study analyzes 14-year outputs from a high-resolution eddy-resolving model to investigate the three-dimensional signature of the Red Sea eddies, their contribution to the air-sea flux, and the eddy-induced transport of heat and salt. Eddies are mostly active and energetic in the central and northern Red Sea. Their associated variability explains ∼8% of the total variance in the surface heat flux, and particularly, ∼39% in the salt flux. The asymmetric eddy structure and meridional gradient drive significant transport of heat and salt across the basin. A negative feedback mechanism is identified that relates the eddy intensity and the meridional steepness of the mixed layer depth in the basin.

This study investigates the impact of extreme heat wave events on long-lived massive corals (Porites spp.) from the central Saudi Arabian Red Sea using trace element (Sr/Ca, Li/Mg, Mg/Ca, U/Ca, B/Ca, and Li/Ca) records preserved in the coral skeleton for the period between 1992 and 2012. Prior to 1998, the trace element records show strong correlations with sea surface temperature. However, during the prolonged high temperature phase associated with the 1998 El Niño event, the seasonal trace element signals were disrupted, which also coincided with a reduction in extension rates. This disruption in normally highly correlated seasonal trace element ratios-sea surface temperature relationships was unusually long, lasting for approximately 2 years in the inner-shelf reef site and nearly 4 years in the outer-shelf reef site. Although the seasonal signal of trace element ratios in both cores eventually stabilized, for the inner-shelf core the amplitude and absolute values in most trace element ratios remained significantly different compared to pre-1998 levels. This suggests that prolonged thermal stress can induce subtle but potentially long-lasting physiological changes that affect the elemental composition of the coral's calcifying fluid. The lack of indication of stress in the core records during later bleaching events (2003, 2005, and 2010) suggests that some of these physiological changes could have induced increased thermal tolerance, particularly for inner-shelf corals, lending support to the capacity for corals to acclimatize.