The Levantine basin (LB) in the Southeastern Mediterranean Sea is a high-risk oil pollution hot spot owing to its dense maritime traffic and intense oil and gas exploration and exploitation activities. In February 2021 the Israeli LB shorelines were impacted by an exceptional tar pollution event (~550 tons; average distribution: ~3 kg tar m-1 front beach) of an unknown oil spill source. Here we report on the immediate numerical modelling assessment of the oil spill propagation and tar distribution; operational use of underwater gliders for tracking water column anomalies of dissolved polycyclic aromatic hydrocarbons (PAHs) and turbidity signals; the beached tar composition and amounts and the short-term response of the microbial population along the ~180 km shoreline. This pollution event emphasizes the need for improving the early warning systems for oil spills and implementing continuous operational monitoring at high-risk, ecologically sensitive and valuable resource areas like the Israeli LB waters.

The Gulf of Aqaba (Gulf of Eilat) is a terminal elongated basin that exchanges water with the northern Red Sea via the Straits of Tiran. The gulf's hydrography exhibits strong seasonal variability, with deep mixing in February-March and stable stratification afterward. Recently, using an oceanic model that simulated the seasonal conditions in the gulf, we demonstrated that a relatively large advected heat and water influx through the straits are responsible for most of the observed rises in temperature and increase in volume of the surface layer during the restratification phase (April-August). Here we investigate the restratification process in the surface layer by using the same oceanic model with the aid of passive tracers that allow tracking the water entering through the straits as it flows northward. We show that the time-varying surface hydrography in the northern Red Sea has a significant influence on the seasonal hydrographic conditions in the gulf. The northern Red Sea water warms monotonically during the restratification phase. As a result, new water that enters the gulf during this phase is warmer than the water that entered previously and therefore the stratification is built up gradually layer by layer. The phase difference between minimal salinity (May) and maximal temperature (September) in the northern Red Sea is responsible for the evolution of subsurface salinity minimum level along the gulf. We also explain the transition to a four-layer exchange flow between August and November.

The Gulf of Aqaba (Gulf of Eilat) is a terminal elongated basin that exchanges water with the northern Red Sea via the Straits of Tiran. The gulf's hydrography exhibits strong seasonal variability, with deep mixing during February-March and stable stratification afterward. We use an oceanic model to investigate the annual cycle of the general circulation and hydrographic conditions in the gulf. We demonstrate that on a subannual time scale, the general circulation deviates from the standard depiction of inverse estuarine circulation. During the restratification season (April-August), the exchange flux with the northern Red Sea is maximal and is driven by density differences between the basins, while atmospheric fluxes actually counteract this exchange flow. The observed warming of the surface layer is mainly due to advection of warm water from the northern Red Sea, with a smaller contribution from surface heating. During the mixing season (September-March), the exchange flux and the advection of heat are minimal and atmospheric fluxes drive convection rather than the exchange flow. We estimate the seasonality of the exchange flow through the Straits of Tiran. The seasonal variability in the exchange flow is large and ranges from 0.04 Sv during early spring to 0.005 Sv during early winter.

We investigate the coupling between the dynamics in the Gulf of Aqaba (Gulf of Eilat, northern Red Sea) and the exchange flow through the Straits of Tiran in response to seasonally varying surface fluxes and northern Red Sea hydrographic conditions. Because the gulf is a relatively small basin, winter mixing between the surface and intermediate layers occurs over most places in the gulf including in the vicinity of the straits, and leads to a maximal exchange flow in the strait. During the spring, warming in the Red Sea forces an influx of warm Red Sea water into the gulf, the surface layer is refilled, and consequently the exchange flow in the straits changes from a maximal to a submaximal flow regime. As a result, the dense wintertime water formation in the gulf and the exchange flow through the strait are strongly coupled on seasonal time scales. In addition, the hydrographic conditions in the northern Red Sea undergo strong seasonality. These characteristics prevent the direct application of current theories for strait-marginal sea systems, which commonly assume steady conditions in the "open ocean" side of the strait and/or an annual mean surface flux over the marginal sea. We explain why the exchange of volume and heat between the Gulf of Aqaba (Gulf of Eilat) and the northern Red Sea is larger during spring-summer despite the net surface buoyancy input into the gulf and why it diminishes during fall-winter despite the large buoyancy loss to the atmosphere. The applicability of the results to other systems is discussed.

We used an oceanic general circulation model to evaluate the sensitivity of the hydrography and circulation of the Red Sea in response to reduced sea level and modified atmospheric conditions during the Holocene. With Holocene sea level close to the modern level, the Red Sea was sensitive to changes in atmospheric conditions, and it only shows a relatively mild response to sea level change. Changes in the monsoon system influence the exchange flow through the Strait of Bab el Mandab, the meridional overturning circulation of the Red Sea, and its hydrography. Forced by humid conditions the (modeled) Red Sea temperature increased by similar to 1.5 degrees C, while when arid conditions were imposed, the temperature decreased by similar to 2.5 degrees C. Similar heating and cooling events during the early and late Holocene are seen in a sea surface temperature record from the northern Red Sea (derived from the temperature sensitive TEX86 molecular biomarker), which suggests that humid conditions prevailed during the early Holocene and more arid conditions prevailed during the late Holocene. The gradual decline in Red Sea temperature between these two time periods suggests a gradual decline in the summer monsoon strength. This monsoon trend and the resulting changes in the Red Sea circulation are supported by the distribution of crenarchaea fossil lipids in Red Sea sediments from this period. Monsoon-driven changes in the exchange flow through the Strait of Bab el Mandab affected the crenarchaea population structure, and therefore, their molecular fossil distribution in the sediments of the Red Sea potentially provides an index for the summer monsoon strength during the Holocene.

We investigate density current formation and flow in the northern Gulf of Eilat, Red Sea, using in situ observations and a high resolution, nonhydrostatic general circulation model. These density currents occur in relatively warm water ∼20°C and are probably the warmest in the world ocean. We demonstrate the intrinsic nonlinearity of density currents by comparing two high‐resolution simulations forced by different heat flux. This nonlinearity, which is poorly represented in global models, is shown here to affect the properties of simulated density currents. Such a bias in simulating density currents in global models may lead to significant biases on the larger scale global ocean circulation and water mass distribution.

The Red Sea is connected to the Indian Ocean via a narrow and shallow strait and exhibits a high sensitivity to atmospheric changes and a reduced sea level. We used an ocean general circulation model to investigate the hydrography and circulation in the Red Sea in response to reduced sea level and modified atmospheric conditions occurring during the Last Glacial Maximum (LGM). The model salinity shows high sensitivity to sea level reduction together with a mild atmospheric impact. Sea level reduction affects the stratification and alters the circulation pattern at the Strait of Bab el Mandab, which experiences a transition from a submaximal flow to a maximal flow. The best correlation to reconstructed conditions during LGM exists when the water depth of the Hanish Sill (the shallowest part in the Strait of Bab el Mandab) is 33 ± 10.75 m, which would be affected by a sea level lowering of approximately 105 m. Our results support the reconstructed maximum salinity of around 57 practical salinity units because of a simple model (that takes into account mixing processes along the strait) and comparison of the surface salinity gradient to reconstructions based on isotopic records from sedimentary cores. The salinity and δ18O are sensitive to the mixing process at the strait, and the sensitivity increases as the sea level is further reduced. A local relative sea level reduction of approximately 105 m is also in close agreement with the inference of the LGM low stand of the sea at the location of the sill based on the ICE‐5G (VM2) model.