The Mediterranean, like the global ocean, is composed of a series of adjacent water masses interleaving with each other both in the horizontal and the vertical. The temperature, salinity, and density vary dramatically from one water mass to the next. Scientists can even pinpoint where these water masses come from and where they are headed.
by P. Malanotte-Rizzoli, A. R. Robinson, W. Roether, B. Manca, A. Bergamasco, S. Brenner, G. Civitarese, D. Georgopoulos, P. J. Haley, S.
Kioroglou, H. Kontoyannis, N. Kress, M. A. Latif, W. G. Leslie, E. Ozsoy, M. Ribera d'Alcala, I. Salihoglu, E. Sansone, and A.Theocharis
During the last decade, oceanographers have focused much attention on the Mediterranean Sea. One reason for the growing interest is that the Mediterranean affects the Northern Atlantic Ocean much more than previously realized. The warm, salty Mediterranean water tongue exits the Gibraltar Straits and spreads throughout the North Atlantic at all depths between 1000 and 2500 meters. The second reason for the surge in interest is the well-recognized role of the Mediterranean Sea as a laboratory for studying ocean processes that are important to global climate.
The Mediterranean Sea is essentially divided into two basins, the eastern and the western. The basins are separated by the shallow Sicily Straits, which prevent the water masses from the deep and bottom layers of the two basins from mixing. Although many theories have been proposed about the Mediterranean circulation and the origin of these water masses, many questions remain unanswered.
Deep/intermediate water masses are produced by heat loss and evaporation fluxes at the air/sea interface in wintertime under favorable wind conditions. In winter, cold, dry air blowing from the mainland over the water produces two effects. First, it causes heat loss from the ocean, which reduces the temperature of the surface layer. Second, it induces evaporation from the sea; that is, the dry wind is enriched with moisture taken from the surface water, which therefore increases its salinity. The surface water mass, becoming colder and saltier, becomes denser. When the wind effect is so strong that the surface water mass becomes denser than the underlying water, convection follows—but it can penetrate only to intermediate levels (300–500 meter depth) or to very deep levels, 1000–2000 meters. This convection process produces a vertically well-mixed water column. When the wind stops, this water mass sinks to the depth where it is neutrally buoyant with the surrounding waters and constitutes the newly formed intermediate/deep water mass.
There may be a direct pathway of the Mediterranean water mass to the northern polar seas along the coast of Europe. This northbound route occurs on all of the isopycnals—surfaces of constant density—in the above depth range along with the classical westward route. On the other hand, the Mediterranean outflow's link to the North Atlantic Deep Water may be indirect. If this is the case, Mediterranean water mixes with the North Atlantic Central waters which, via the Gulf Stream and the North Atlantic Current, feed the Nordic Seas. Be it direct or indirect, it is clear that the Mediterranean water mass crucially affects North Atlantic Deep Water.
The Eastern Mediterranean is particularly important for studying global ocean processes. The Mediterranean salty/warm water mass exiting from Gibraltar is formed in the Eastern Mediterranean along the route of the water that connects the western and eastern basins in the uppermost 300-meter layer. Cold, light Atlantic Water flows in at Gibraltar. This water mass spreads eastward as it undergoes progressive modifications, becoming warmer and saltier and reaches the Eastern Levantine as Modified Atlantic Water. Here intense evaporation in the wintertime and associated heat loss under surface winds change the Modified Atlantic Water into a different water mass, the Levantine Intermediate Water, which is saltier, denser, and sinks to intermediate depths of 300 to 500 meters.
The Levantine Intermediate Water moves from the Northeastern Levantine, crosses the entire Mediterranean, and exits from Gibraltar. The water masses formed in the Northwestern Mediterranean (the Lions Gulf) contribute very little to the water leaving Gibraltar. They remain confined in the western basin in the layers below 2000 meters. Thus the Eastern Levantine Sea is the "engine" that drives the upper Mediterranean.
Physical Oceanography of the Eastern Mediterranean, a program sponsored by the United Nations, has studied the Eastern Mediterranean since 1985. Researchers with the program studied circulation and physical pro- cesses from 1985 to 1990, resulting in three unexpected findings.
They discovered a water mass in the deep-bottom layers of water that originates in the Southern Adriatic and spreads into the Eastern Levantine, the Eastern Mediterranean "conveyor belt." Also found were interacting motions that define the general circulation of the region, such as jets and strong currents that produce eddies that detach and fill out the basin interior. And two convective regions with related water mass formation were found. The first is a deep convection cell in the Southern Adriatic, where the Eastern Mediterranean Deep Water was formed between 1985 and 1987. Second, a convective region, more extensive than previously recognized, surrounds the Levantine Rhodes gyre where intermediate convection leads to the LIW formation.
In 1990, the program evolved into an interdisciplinary project that studied biology and chemistry as well as ocean mixing. Fieldwork began with a basin-wide survey carried out in October 1991 by research vessels from Greece, Israel, Turkey, and Italy. A second survey was carried out in March 1992 in the Ionian and Cretan Seas by two of the research vessels. The information collected by the two cruises is helping to study the inorganic nutrients and biological properties of the basin.
A major experiment was carried out in winter 1995 to study how the Levantine Intermediate Water forms. The figure below shows the area covered during the survey by Germany's R/V Meteor in January and February 1995. Large dots indicate hydrographic and tracer stations where the physical, chemical, and biological parameters were measured.
The two diamond-shaped regions between the islands of Rhodes and Cyprus show where the Levantine Intermediate Water is formed. This is where intensive fieldwork was conducted during four surveys carried out upon research vessels from Turkey, Italy, Greece, and Israel in 1995. The black lines in the figure show where the Meteor traveled, and the colors indicate the temperature of water at 125 meters depth on one day at sea in the Eastern Mediterranean.
The first major result that emerged from the preliminary analysis was completely unexpected: the Eastern Mediterranean deep waters were in an entirely new configuration. Up until 1987, oceanographic observations showed that the major source of deep water in the basin was the Southern Adriatic Sea. The winter 1995 observations show instead that the deep water mass of the entire basin is formed in the Aegean Sea, and that it exits through the straits that separate the various islands surrounding the Aegean Sea (see figure). Because this water is higher in salinity and density, it spreads at great depths, displacing the older water of Adriatic origin upward and to the west. The Eastern Mediterranean is a "small" laboratory for processes occurring in the global ocean, where similar changes in the Atlantic conveyor belt have been hypothesized to have occurred in the geological past, but have never been observed in present times.
Source: Eos, August 6, 1996, p. 305.
I first became interested in science at age 9 when I decided I would become a mathemathics teacher, as math was my favorite subject.
In high school I discovered physics and realized that physics investigates the basic principles that govern the world in which we live, from the micro (atomic) scale to the macro (cosmological) scale. Mathematics is simply the language of physics. I earned an Italian Doctorate, which is roughly equivalent to a Master's degree in the United States, in theoretical (elementary particle) physics from the University of Padua.
In 1970, after working for a year at the University of Padua as a postdoctoral associate, I went to work in Venice in a research laboratory of the Italian National Research Council to study the"Venice problems," which are double in nature. Geologically, there are lots of subsidence in Venice due to the collapse of underground aquifers depleted of water by industrial pumping; oceanologically, high water connected to storm surges of the Adriatic Sea is a problem. Having grown up in Venice, I was familiar with the effects of high water. During the famous flooding of November 1966, I was trapped at home for 3 days! My first job at the lab was to construct a numerical model to predict the storm surge, and that is why I became a physical oceanographer.
As I had had no basic training in oceanography, I earned a Ph.D. at the Scripps Institution of Oceanography in San Diego, Calif., while keeping my job in Venice—a long commute. From 1975 to 1978, I spent half the year working in Italy on the Venice problems and the other half at Scripps working toward my Ph.D. thesis on a completely different topic.
In 1980, I was offered a position at MIT. I obviously was interested, even though this meant giving up a tenured job in Italy to start all over again from the beginning and emigrating for good. I have been at MIT ever since, and I am now a full professor.
I am currently interested in theoretical modeling of the ocean general circulation on different scales, from the ocean basin scale (Northern Atlantic) to a regional scale (Gulf Stream System) to enclosed seas (Mediterranean and Black Seas).
My advice to students is, always do and study what excites you the most, be ready to accept intellectual challenges, and always aim to higher goals and achievements.
This is the only way to achieve the highest intellectual satisfaction. Never start a vast project with half-a-vast idea ... .
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