M. A. Latif

On the Physical Oceanography of the Turkish Straits

The Bosphorus and the Dardanelles Straits and the Sea of Marmara constitute a system through which exchange of Mediterranean and the Black Sea waters takes place. The two layer flow regime displays temporal and spatial variability on a wealth of scales. An assessment of the volume fluxes for the various elements of the system, based on recent hydrographic investigations, shows that a major portion of the Mediterranean flow entering through the Dardanelles is transported back to the Aegean Sea due to upward mixing induced by internal hydraulic adjustments of the exchange flow in the straits and by wind in the Sea of Marmara proper. The jet-like Bosphorus outflow in the exit region of the Marmara Sea also has a substantial contribution to the overall upward mixing. A mesoscale anticyclonic eddy to the right of the outflow off the Thracian coast is a quasi-permanent feature of the system. Hydraulic controls in the Bosphorus strait result in a maximal exchange, while a submaximal exchange exists in the Dardanelles. The Mediterranean inflow enters the Black Sea on an essentially continuous basis, with only few, short interruptions.

General Circulation of the Eastern Mediterranean

Abstract A novel description of the phenomenology of the Eastern Mediterranean is presented based upon a comprehensive pooled hydrographic data base collected during 1985–1987 and analyzed by cooperating scientists from several institutions and nations (the POEM project). Related dynamical process and modeling studies are also overviewed. The circulation and its variabilities consist of three predominant and interacting scales: basin scale, subbasin scale, and mesoscale. Highly resolved and unbiased maps of the basin wide circulation in the thermocline layer are presented which provide a new depiction of the main thermocline general circulation, composed of subbasin scale gyres interconnected by intense jets and meandering currents. Semipermanent features exist but important subbasin scale variabilities also occur on many time scales. Mesoscale variabilities modulate the subbasin scale and small mesoscale eddies populate the open sea, especially the south-eastern Levantine basin. Clear evidence indicates Levantine Intermediate Water (LIW) to be present over most of the Levantine Basin, implying that formation of LIW is not localized but rather is ubiquitous. The Ionian and Levantine basins are confirmed to form one deep thermohaline cell with deep water of Adriatic origin and to have a turnover time of one and a quarter centuries. Prognostic, inverse, box and data assimilative modeling results are presented based on both climatological and POEM data. The subbasin scale elements of the general circulation are stable and robust to the dynamical adjustment process. These findings bear importantly on a broad range of problems in ocean science and marine technology that depend upon knowledge of the general circulation and water mass structure, including biogeochemical fluxes, regional climate, coastal interactions, pollution and environmental management. Of global ocean scientific significance are the fundamental processes of water mass formations, transformations and dispersion which occur in the basin.

Circulation in the surface and intermediate layers of the Black Sea

Abstract Circulation features of the Black Sea are presented based upon a basin-scale survey carried out in September–October 1990. The circulation pattern for the upper 300–400 dbar consists of a cyclonically meandering Rim Current, a series of anticycloniceddies confined between the coast and the Rim Current, and a basin-wide, multi-centered cyclonic cell in the interior of the basin. In contrast to prior investigations, although the currents are much weaker as compared with those in the upper layer, the intermediate depth (defined here between 500 and 1000 dbar) circulations reveal considerable structural variability. This involves counter-currents, shift of eddy centers, coalescence of eddies, and associated sub-basin-scale recirculation cells separated by the meandering Mid-Basin Current system. A descriptive synthesis of the upper layer circulation, combining the present results with earlier findings, identifies the quasi-permanent and recurrent features even though the shape, position, strength of eddies and meander pattern, and the bifurcation structure of currents vary.

Modeling of Hydraulically Controlled Exchange Flow in the Bosphorus Strait

Abstract Recent hydrographic observations obtained in the Bosphorus Strait illustrate several features of the flow that may be related with the internal hydraulics. A two-layer numerical model indicates that the two-way exchange flow may indeed be subject to a series of internal hydraulic adjustments along the strait due to morphological features such as sills, a contraction and abrupt expansion of the width of the strait. The model identifies three distinct regions of the supercritical flow. The lower-layer flow of the Marmara Sea origin is directed to the north towards the Black Sea in a progressively thinning layer and is controlled by the sill located near the Black Sea entrance of the strait. The upper-layer water of the Black Sea origin flows in the opposite direction and is controlled upon reaching the constricted region located about 10–12 km away from the Marmara end of the strait. The upper-layer flow is then matched to the subsequent subcritical conditions by undergoing an internal hydraulic ju...

Observations of the Mediterranean inflow into the Black Sea

Abstract The Mediterranean inflow issuing from the Bosphorus Strait has been documented to enter the Black Sea essentially confined in a 10-km long channel which is a continuation of the strait over the adjacent shelf. The width of the channel is between 500 and 1000 m. A 3.5-km-long sill, with a depth of 60 m, is situated in the channel at its beginning, just north of the end of the strait. The Mediterranean water flows into the Black Sea essentially on a continuous basis throughout the year, but it may be interrupted for short durations under unusually strong and persistent winds. After exiting from the channel, the Mediterranean inflow spreads in a thin layer above the bottom and continues in a generally northerly direction towards the shelf break.

A synthesis of the Levantine Basin circulation and hydrography, 1985-1990

Abstract The Levantine Basin circulation derived from recent data consists of a series of sub-basin-scale to mesoscale eddies interconnected by jets. The basin-scale circulation is masked by eddy variability that modulates and modifies it on seasonal and interannual time scales. Long-term qualitative changes in the circulation are reflected in the bifurcation pattterns of ther mid-basin jets, relative strengths of eddies and the hydrographic properties at the core of these eddies. Confinement within the Basin geometry strongly influences the co-evolution of the circulation features. Surface measurements, satellite images and the mass field indicate an entire range of scales of dynamical features in the region. The complexity of the circulation is consistent with the basin-wide and mesoscale heterogeneity of the hydrographic properties. The interannual variability of LIW (Levantine Intermediate Water) formation in the region appears correlated with the changes in the circulation. Wintertime convective overturning of water masses reach intermediate depths and constitute a dominant mechanism of LIW formation, especially in anticyclonic eddies and along the coasts of the northern Levantine Basin.

A review of the Levantine Basin circulation and its variability during 1985–1988

Abstract The variability of the Levantine Basin circulation and hydrography is reviewed based on a collection of recent data sets. The major emphasis is placed on the complexity of the associated dynamics. The region is shown to be populated with synoptic and mesoscale dynamic features. In addition to the complexity arising due to the heterogeneity of water masses and the variability of the atmospheric and thermohaline forcing, the confines of the relatively small basin causes the sub-basin-scale gyres to be in close contact with each other, resulting in interacting, basin-wide turbulent features. The bifurcation of the mid-Levantine jet near Cyprus is variable on interannual time-scales, the amount of bifurcation of the fluxes being dependent on the evolution of the circulation in the multi-connected domain and the relative intensities of the sub-basin-scale gyres. During the 3-year observation programme, qualitative changes are identified in the general circulation. The flow encircling Cyprus is partially blocked in the first phase of the experiments. Later, the two basins on the north and east sides of Cyprus are flushed with new water masses carried in the cores of incident eddies, and a new pattern of basin-wide circulation is established, with a major part of the mid-basin jet flowing coherently along the mainland coasts and cyclonically around Cyprus. As a consequence, the general circulation of the Levantine Basin appears considerably different and more complex than the traditional descriptions of it.

Quasi‐steady exchange flow in the bosphorus

Current meter moorings and high-resolution surveys in the Bosphorus reveal important details of the exchange flow. During early September 1994, the flow was quasi-steady and demonstrated strong mixing, particularly in the surface layer after it entered the principal contraction of the strait. Composite Froude numbers in the contraction are lower than expected, consistent with recent modeling that shows friction producing significant deviations from predictions of inviscid two-layer hydraulic theory.

On the Dynamics of the Southern Black Sea

The geostrophic circulation and distributions of the Cold Intermediate and the Mediterranean water masses along the Turkish coast of the Black Sea are described on the basis of hydrographic data collected during 1987–1989 surveys of the R/V Bilim. The regional circulation was found to consist of a meandering rim current conforming mainly on the topographic slope and a series of anticyclonic eddies attached to the shelf break. The eddies, observed in the period of the surveys, seem to be quasi-permanent features and are controlled by the topography and also modified by the barotropic-baroclinic instability of the flow. Further details and structural variability of the circulation were inferred by satellite imagery. The distribution of the CIL waters was found to follow the regional circulation. The characteristics of the CIL are continually modified as it is advected eastward by the rim current and partially entrapped in the anticyclonic eddies. The CIL waters are identified by core temperatures of about 6.5 °C in the Bosphorus exit region and 7.0–7.2 °C in the southeastern part of the Black Sea. The Mediterranean underflow, crossing the the southwestern Black Sea shelf region, is subject to continuous mixing due to interaction with the CIL waters. By the time the Mediterranean effluent reaches the shelf break (at depths of 100–150m), it is identified by a colder and slightly less saline water mass relative to the ambient conditions. This modified water mass then intrudes into the deeper levels of the basin in the form of patches of colder and relatively oxygen-rich water, and leads to the partial ventilation of the subhalocline waters.

Measuring the Sea: Marsili’s Oceanographic Cruise (1679–80) and the Roots of Oceanography

ABSTRACTThe first in situ measurements of seawater density that referred to a geographical position at sea and time of the year were carried out by Count Luigi Ferdinando Marsili between 1679 and 1680 in the Adriatic Sea, Aegean Sea, Marmara Sea, and the Bosporus. Not only was this the first investigation with documented oceanographic measurements carried out at stations, but the measurements were described in such an accurate way that the authors were able to reconstruct the observations in modern units. These first measurements concern the “specific gravity” of seawaters (i.e., the ratio between fluid densities). The data reported in the historical oceanographic treatise Osservazioni intorno al Bosforo Tracio (Marsili) allowed the reconstruction of the seawater density at different geographic locations between 1679 and 1680. Marsili’s experimental methodology included the collection of surface and deep water samples, the analysis of the samples with a hydrostatic ampoule, and the use of a reference wate...