The Me­di­ter­ra­nean differs not only from the open ocean with respect to the feebleness and irregularity of its tides, but it is likewise without a great stream-current keeping in constant circulation the whole body of its waters. The currents which have been observed in various divisions of the Me­di­ter­ra­nean can be ascribed only to local causes. An Italian geographer of the last century, Montanari, has {27} advanced an hypothesis of a great circuit current which entered the Me­di­ter­ra­nean through the Strait of Gibraltar, and, after having washed the shores of Africa as far as Egypt, returned to the west along those of Asia and Europe; but careful observers have vainly endeavoured to discover its existence. They have met only with local currents, produced by an indraught of the waters of the Atlantic, by winds, by the floods of rivers, or by an excess of evaporation. One of these currents sets along the coasts of Morocco and Algeria from west to east; another flows along the Italian coast of the Adriatic from north to south; and a third from the mouth of the Rhone in the direction of Cette and Port Vendres. In fact, the configuration of the sea-bottom, and particularly the shoal between Sicily and Tunis, precludes the existence of any but surface currents in the Me­di­ter­ra­nean.

Amongst the local currents the existence of which has been most clearly established are those which convey the waters of the Sea of Azof into the Black Sea, and those of the latter into the Archipelago. The Don more than makes up for the loss by evaporation in the Sea of Azof, and its surplus waters find an exit through the Strait of Kerch into the Black Sea. Similarly the waters of the Dniester, the Dnieper, the Rion, and of the rivers of Asia Minor, and, above all, of the Danube, which by itself conveys a larger volume of water into the Black Sea than all the others combined, are discharged through the Bosphorus and the Dardanelles into the Archipelago. On the other hand, the Archipelago returns to the Black Sea, by means of a submarine counter-current and of lateral surface currents, a certain quantity of salt water for the fresh water which it receives in excess. This exchange accounts for the salineness of the waters of the Black Sea. The volume of fresh water discharged into it by the Danube and other rivers is so large that in the course of a thousand years its waters would become perfectly fresh, if there did not exist these compensatory highly saline counter-currents.

Analogous phenomena take place at the other extremity of the Me­di­ter­ra­nean. Evaporation there is excessive, owing to the neighbourhood of the burning sands of the deserts, the winds from which blow freely over the sea, absorbing the vapours and dispersing the clouds. The loss by evaporation amounts to at least seven feet in the course of a year, and as the annual rainfall is estimated to amount to twenty inches only, and the volume of water discharged annually by all the tributary rivers of the Me­di­ter­ra­nean, if uniformly spread over its surface, would hardly exceed ten inches in depth, there exists thus an excess of evaporation amounting annually to more than four feet; and this excess has to be made good by an inflow of the waters of the Atlantic, which takes place through the Strait of Gibraltar, whose volume far exceeds that of the Amazon in a state of flood. This inflow of the waters of the Atlantic is felt, as a current, as far as the coasts of Sicily, and, like all other currents, it is bounded by lateral currents flowing in a direction contrary to that of the main current. During ebb the insetting Atlantic current takes up the whole of the strait, but when the tide rises the Me­di­ter­ra­nean resists more successfully the pressure of the ocean, and this struggle gives birth to {28} two counter-currents, one of which skirts the coast of Europe, the other that of Africa between Ceuta and Cape Spartel; the latter is the larger and more powerful of the two. In addition to these, there exists a submarine current, which conveys the highly saline and heavier waters of the Me­di­ter­ra­nean out into the Atlantic.

The quantity of salt held in solution in various parts of the Me­di­ter­ra­nean differs widely, as the submarine ridges and shoals which divide it into separate basins do not permit its waters to mingle as freely as in the open ocean. Owing to the excess of evaporation, the quantity of salt is greater on the whole than in the Atlantic, and this is the case more particularly on the coast of Africa. But in the Black Sea it is far less, and near the mouths of some of the large rivers which enter that sea the water is almost fresh.[8]

The temperature of the Me­di­ter­ra­nean is affected by the same causes which produce its varying salineness, viz. the existence of shoals and banks, which separate it into distinct sub-basins. In the open ocean the currents convey to all latitudes large bodies of water, some of them heated by a tropical sun, others cooled by contact with the ice of the polar regions. But these layers of unequal density are regularly superimposed one upon the other, owing to the differences in their temperature: the warm water remains on the surface, whilst the cold water descends to the bottom. In the Me­di­ter­ra­nean an analogous superimposition exists only to a depth of 110 fathoms, which is the depth of the Atlantic current, flowing into it through the Strait of Gibraltar. If a thermometer be lowered to a greater depth it will indicate no further decrease of temperature, and the immense body of water, remaining almost still at the bottom of the Me­di­ter­ra­nean, has an equable temperature of about 56° F. Observations made at depths varying between 110 and 1,640 fathoms have always exhibited the same result. Professor Carpenter believes, however, that the abyssal waters of some of the volcanic regions have a somewhat higher temperature, which may be due to the presence of lava in a state of fusion.

II.—ANIMAL LIFE. FISHERIES AND SALT PANS.

Another remarkable feature of the abyssal waters of the Me­di­ter­ra­nean consists in their poverty of animal life. No doubt there is some life; the dredgings of the Porcupine and the telegraph cables, which, on being brought to the surface, were found to be covered with shells and polypes, prove this. But, compared with those of the ocean, the depths of the Me­di­ter­ra­nean are veritable deserts. Edward Forbes, who explored the waters of the Archipelago, arrived at the conclusion that their abyssal depths were entirely devoid of life, but he was wrong when he assumed an exceptional case like this to represent a universal law. Carpenter thinks that this absence of life in the depths of the Me­di­ter­ra­nean is due to the great quantity of organic remains which is carried into it by the rivers. These remains absorb the oxygen of the water, and part with their carbonic acid, which is detrimental to {29} animal life. In numerous instances the water of the Me­di­ter­ra­nean contains only one-fourth the normal quantity of the former gas, but fifty per cent. in excess of the latter. To the presence of these organic remains the Me­di­ter­ra­nean is probably indebted for its beautiful azure colour, so different from the black waters of most oceans. This blue, then, which is justly celebrated by poets, would thus be caused by the impurity of the water. M. Delesse has shown that the bottom of nearly the whole of the Me­di­ter­ra­nean is covered with ooze.

The regions of the Me­di­ter­ra­nean immediately below the surface abound in animal life, particularly on the coasts of Sicily and Southern Italy; but nearly all species, whether fish, testacea, or others, are of Atlantic origin. The Me­di­ter­ra­nean, in spite of its vast extent, as far as its fauna is concerned, is nothing but a gulf of the Lusitanian Ocean. Its longitudinal extension and the similarity of climate in its various portions have favoured the migration of animals through the Strait of Gibraltar as far as the coasts of Syria. At the same time, animal life is most varied near this point of entry, and the species met with in the western basin are generally of greater size than those which exist in the eastern. A very small proportion of non-Atlantic species recalls the fact that the Me­di­ter­ra­nean formerly communicated with the Red Sea and the Indian Ocean. But amongst a total of more than eight hundred molluscs there are only about thirty which have reached the seas of Greece and Sicily through the ancient straits separating Africa from Asia, instead of through the Strait of Gibraltar.[9] The diminution in the number of species in an easterly direction becomes most striking when we reach the narrow channel of the Dardanelles and the Bosphorus. The Black Sea, in fact, differs essentially from the Me­di­ter­ra­nean proper as regards temperature. It is refrigerated by north-easterly winds sweeping over its surface, to the extent even of portions of it becoming now and then covered with a thin coating of ice, adhering to the coast. The Sea of Azof has frequently disappeared beneath a thick crust of ice, and even the whole of the Black Sea has been frozen over in winters of exceptional severity. The cold surface waters, together with those conveyed into the Black Sea by large rivers, descend to the bottom, and prove most detrimental to animal life. Echinodermata and zoophytes are not met with at all in the Black Sea; certain classes of molluscs, already rare in the Levantine Sea and the Archipelago, are likewise absent; and the total number of species of molluscs is only one-tenth of what it is in the Me­di­ter­ra­nean. Fish are numerous as far as individuals go, but their species are few. In fact, the fauna of the Black Sea appears to resemble that of the Caspian, from which it is cut off, rather than that of the Greek seas, with which the Sea of Marmara connects it.

In addition to the species which have found a second home in the Me­di­ter­ra­nean, there are some that must still be looked upon as visitors. Such are the sharks, which extend their incursions to the seas of Sicily, to the Adriatic, and even to the coasts of Egypt and Syria. Such, also, are the larger cetacea—whales, rorquals, and sperm whales—whose visits, however, are confined now to the Tyrrhenian {30} basin, and become less frequent from century to century. The tunny-fish of the Me­di­ter­ra­nean are also visitors from the coasts of Lusitania. First-rate swimmers, they enter through the Strait of Gibraltar in spring, ascend the whole of the Me­di­ter­ra­nean, make the tour of the Black Sea, and return in autumn to the Atlantic, after having accomplished a journey of some 5,600 miles. In the opinion of the fishermen the tunnies go upon their travels in three immense divisions or shoals, and it is the central shoal which visits the coasts of the Tyrrhenian Sea, and consists of the largest and strongest fish. Each of the three divisions appears to be composed of individuals about the same age. For mutual protection they swim in troops, for they are preyed upon by enemies innumerable. Dolphins and other fish of prey follow their track, but their great destroyer is man. In the summer the tunny fishery, or tonnaro, is carried on in numerous bays of Sicily, Sardinia, Naples, and of Provence. Enormous structures consisting of nets enclose these bays, and they are ingeniously arranged so as to close gradually around the captured fish, which, passing from net to net, find themselves at last in the “chamber of death,” where they are massacred. Millions of pounds of flesh are annually obtained from these floating “slaughter-houses,” yet the tunny appears year after year in multitudes, and on the same coasts. There may have been a slight decrease in the number, but their closely packed masses still invade the “Golden Horn” of Byzance and other bays, as they did when first they attracted the attention of Greek naturalists.

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