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On 27 June, a 1-2-m high wave struck the beaches of Odessa, the third largest Ukrainian city, and the neighbouring port-town Illichevsk (northwestern Black Sea). Throughout the day, prominent seiche oscillations were observed in several other ports of the Black Sea. Tsunamigenic synoptic conditions were found over the Black Sea, stretching from Romania in the west to the Crimean Peninsula in the east. Intense air pressure disturbances and convective thunderstorm clouds were associated with these conditions; right at the time of the event, a 1.5-hPa air pressure jump was recorded at Odessa and a few hours earlier in Romania. We have utilized a barotropic ocean numerical model to test two hypotheses: (1) a tsunami-like wave was generated by an air pressure disturbance propagating directly over Odessa (“Experiment 1”); (2) a tsunami-like wave was generated by an air pressure disturbance propagating offshore, approximately 200 km to the south of Odessa, and along the shelf break (“Experiment 2”). Both experiments decisively confirm the meteorological origin of the tsunami-like waves on the coast of Odessa and imply that intensified long ocean waves in this region were generated via the Proudman resonance mechanism while propagating over the northwestern Black Sea shelf. The “Odessa tsunami” of 27 June 2014 was identified as a “beach meteotsunami”, similar to events regularly observed on the beaches of Florida, USA, but different from the “harbour meteotsunamis”, which occurred 1-3 days earlier in Ciutadella (Baleares, Spain), Mazara del Vallo (Sicily, Italy) and Vela Luka (Croatia) in the Mediterranean Sea, despite that they were associated with the same atmospheric system moving over the Mediterranean/Black Sea region on 23-27 June 2014. [ABSTRACT FROM AUTHOR]

The system composed by the two narrow Straits, Dardanelles and Bosphorus, and the Marmara Sea is known as the Turkish Straits System (TSS). The scientific questions on the role of the TSS in coupling the adjacent basins of the Mediterranean and Black Seas with highly contrasting properties and in a region of high climatic variability can only be answered by model predictions of the processes that determine the integral properties of the coupled sub-systems. This can only be achieved if the entire TSS is modeled as a finely resolved integral system that appropriately accounts for the high contrasts in seawater properties, steep topography, hydraulic controls, fine and meso-scale turbulence, nonlinear and non-hydrostatic effects, thermodynamic states and an active free-surface in the fullest extent, based on well represented fluid dynamical principles. In this study the MITgcm (MIT General Circulation Model) is used at very high resolution to study this extreme environment that needs to be represented as a whole and with the full details of its highly contrasting properties. The capability of MITgcm to represent the two-layer exchange dynamics both in the straits and in the Marmara Sea is examined. The non-uniform grid and the vertical resolution implemented have demonstrated to be suitable to capture the fine scales within the two Straits and also to well represent mesoscale in the Marmara Sea. The response of the currents and density structure over the water column to different net flow is also examined through the setup of experiment with varying net barotropic volume fluxes. [ABSTRACT FROM AUTHOR]

The Mediterranean Sea circulation has been simulated by means of three different implementations of the MITgcm (MIT General Circulation Model). The three model domains extend over the same model domain and share the same surface forcing and lateral boundary conditions. The first model has been implemented at a horizontal resolution of 1/12° with 72 vertical z-levels, while the remaining two models use a nonuniform curvilinear orthogonal grid, having a maximum horizontal resolution of about 1/200° in the Strait of Gibraltar, degrading eastward down to a regular grid with a 1/16° resolution, and 72 vertical levels. The last two models differ in the inclusion/exclusion of tidal forcing. Comparison with observed data shows that the overall surface and intermediate circulation simulated by the 1/12° model reproduces the main features of the basin-scale circulation reasonably well. From the comparison of the two additional higher resolution experiments performed with and without tidal forcing, it appears that the tidal forcing has a not negligible impact on the simulated circulation. [ABSTRACT FROM AUTHOR]

The Eastern Weddell Ice Shelves (EWIS) are believed to modify the water masses of the coastal current and thus preconditions the water mass formation in the southern and western Weddell Sea. We apply various ocean warming scenarios to investigate the impact on the temperature–salinity distribution and the sub-ice shelf melting in the Eastern Weddell Sea. In our numerical experiments, the warming is imposed homogeneously along the open inflow boundaries of the model domain, leading to a warming of the warm deep water (WDW) further downstream. Our modelling results indicate a weak quadratic dependence of the melt rate at the ice shelf base on the imposed amount of warming, which is consistent with earlier studies. The total melt rate has a strong dependence on the applied ocean warming depth. If the warming is restricted to the upper ocean (above 1,000 m), the water column (aside from the mixed surface layer) in the vicinity of the ice shelves stabilises. Hence, reduced vertical mixing will reduce the potential of Antarctic Bottom Water formation further downstream with consequences on the global thermohaline circulation. If the warming extends to the abyss, the WDW core moves significantly closer to the continental shelf break. This sharpens the Antarctic Slope Front and leads to a reduced density stratification. In contrast to the narrow shelf bathymetry in the EWIS region, a wider continental shelf (like in the southern Weddell Sea) partly protects ice shelves from remote ocean warming. Hence, the freshwater production rate of, e.g., the Filchner–Ronne Ice Shelf increases much less compared with the EWIS for identical warming scenarios. Our study therefore indicates that the ice-ocean interaction has a significant impact on the temperature-salinity distribution and the water column stability in the vicinity of ice shelves located along a narrow continental shelf. The effects of ocean warming and the impact of increased freshwater fluxes on the circulation are of the same order of magnitude and superimposed. Therefore, a consideration of this interaction in large-scale climate studies is essential. [ABSTRACT FROM AUTHOR]

Lake Vostok, isolated from direct exchange with the atmosphere by about 4 km of ice for millions of years, provides a unique environment. This inaccessibility raises the importance of numerical models to investigate the physical conditions within the lake. Using a three-dimensional numerical model and the best available geometry, we test different parameter settings to define a standard model configuration suitable for studying flow in this subglacial lake. From our model runs we find a baroclinic circulation within the lake that splits into three different parts: Along a topographic ridge in the northern part of Lake Vostok, bottom water masses are transported eastward, diverging away from the ridge. In the lake’s surface layer, the flow in these two vertical overturning cells has opposite directions. In the southern part of the lake, where freezing occurs across about 3,500 km2, two opposing gyres split the water column vertically. The general flow is stronger in the southern basin with horizontal velocities in the order of 1 mm/s. The strongest upwelling, found in the eastern part of this basin, is about 25 μm/s. We estimate the lower limit of the overturning timescale to be about 2.5 years vertically and 8.6 years horizontally. The basal mass loss of ice from the ice sheet floating on the lake is 5.6 mm/year (equivalent to a fresh water flux of 2.78 m3/s, or a basal ice loss of 0.09 km3/year). This imbalance indicates either a constant growth of the lake or its continuous (or periodical) discharge into a subglacial drainage system. [ABSTRACT FROM AUTHOR]

Abstract: In recent years it has been documented that deep-water coral reefs of the species Lophelia pertusa are a major benthic habitat in Norwegian waters. However, basic information about the biology and ecology of this species is still unknown. Lophelia live and thrive under special environmental conditions of which factors such as temperature, water depth, water movement and food supply are important. The present work explores the hypothesis that Lophelia forms reefs in places where the encounter rate of food particles is sufficiently high and stable over long periods of time for continuous growth. This is done by relating the distribution of reefs with the results of numerical ocean modelling. Numerical simulations have been performed with an idealized bottom topography similar to what is found outside parts of the Norwegian coast. In the simulations the model is first forced with an along slope jet and then with an idealized atmospheric low pressure. The model results show that the encounter rates between the particles and the water layer near the seabed are particularly high close to the shelf break. This may indicate that many Lophelia reefs are located along the shelf edges because the supply of food is particularly good in these areas. A sensitivity study of the particle supply in the area close to the seabed for increasing latitude has also been done. This shows that the Ekman transport in the benthic layer tends to create a steady supply of food for benthic organisms near the shelf edge away from the equator. [Copyright &y& Elsevier]

Abstract: Sigma coordinate ocean models, or models based on more generalised topography following coordinate systems, are presently widely used in oceanographic studies. Terrain following models are attractive because of their abilities to resolve the surface and bottom layers. However, the internal pressure gradient estimation is problematic in such models, and artificial pressure gradients may create artificial flow. In fine resolution studies where topography and stratification is well resolved, the artificial flow due to erroneous pressure gradients is small because the errors typically converge to zero with the square of the grid size. In coarse resolution studies, however, there may still be large erroneous pressure gradients that may create strong artificial flow. To avoid this, larger horizontal viscosities than one would like to apply from physical considerations, are applied in most studies so far. This means that smaller scale phenomena in the flow will be poorly represented. The response of the flow to the pressure errors in long time simulations with low horizontal viscosity is very important. In this study it is demonstrated that the choice of the time stepping method may affect the growth of the erroneous flow considerably. Increasing the implicit nature of the time stepping method, will generally reduce the growth. Recently many oceanic model studies have been performed with models that allow non-hydrostatic pressure effects. In the present study it is shown that when allowing the flow to adjust to non-hydrostatic pressure, the growth of the flow due to internal pressure errors may be strongly affected. [Copyright &y& Elsevier]