Some Physicogeographic Facts

The Po.

This river has in general an easterly course. Together with the Volano, Adige, and Brenta Rivers, it has formed a large common delta between the Lagoon of Venice in the north and the Lagoon of Comacchio in the south. The existence of five ancient mouths of the Po are evidence of the migrations of this river. We do not have sufficient data to identify chronologically the activity periods of these mouths with any climatic periods. All the same, there is some reason to assume that the river tended to deviate equatorward during cold periods and poleward during warm periods. For example, during the second cold period (antiquity), the mouth of the Po was not far from the Comacchio lagoon, that is, more toward the south than at present. The famous Etruscan port of Spina, which reached its high point in the fourth century B.C., was situated on the southern branch of the Padus (as the Po was then called).

With the onset of the warm period the mouth of the Po moved toward the pole, and the southern branches became silted up. Moreover, whereas in antiquity the site of the city was quite high up above the sea, during the early Middle Ages it gradually sank down below sea level, under the influence of the eustatic factor and as a result of the "water-overflow" effect. The city of Spina lost its importance as a major trading center and gradually went into a decline. By the first centuries A.D. there was only a small village on the site.

Northern part of Mediterranean.

The northern Mediterranean is situated in approximately the same latitudes, and in the same general locality relative to the oceans and continents, as the Azov-Black Sea basin. Consequently, the long-term level fluctuations in the part of the Mediter ranean north of the Gibraltar parallel are synchronous with those in the Azov-Black Sea basin, the amplitudes of the fluctuations being greater in the direction of the pole.

The course of the level variations in the northern Mediterranean during the last 2500 years is indicated by the behavior of the world's oldest "tide gauge," the temple of Serapis. This temple was built on the shore of the Bay of Naples, near the town of Pozzuoli, at the end of the second period of climatic cooling (second century B.C., or, according to some sources, somewhat later), At the beginning of the warm period in the early Middle Ages, the temple was found to be several meters below sea level. Then, during the third cold period (late Middle Ages), it came out of the water completely (Figure 13). The low level of the sea at this time is also verified by the fact that in 1501 to 1503 the king of Naples sold (at a low price) some pieces of land which had been freed from the sea; in particular, he presented the area adjoining Pozzuoli to the university of that town.

In accordance with the warmer climate during the present period, the temple of Serapis has once again begun to be submerged, and its floor is already more than 1.5 meters below sea level.

The sea is also advancing in other parts of the northern Mediterranean. For example, during each ten-year period Venice sinks no less than 5 cm into the sea. A place situated on the lower reaches of the Po became submerged under 18.7 cm of water between 1902 and 1950. This raising of the level of the sea should explain the abrasive character of the shores in the northern Mediterranean, and also the fact that there are not a considerable number of beaches there.

The World Ocean.

Data from precise grading measurements indicate that during the present period the level of the World Ocean has a slope from the poles to the equator. As Shokal'skii (1959, p. 80) points out, the position of the average multiannual sea level from south to north is rising gradually. This has been noted in North America for both the Atlantic and Pacific, and it has been verified in the Soviet Union. However, Shokal'skii does not cite the reason for the indicated phenomena. Apparently, the phenomena in question are caused by the secular decrease in the diurnal rotation velocity of the Earth (and thus in the centrifugal forces), which is in turn a result of the present climatic warming.

We have considered, unfortunately in a very cursory and fragmentary way, the "behavior" of more than 30 hydrological objects (13 water bodies and 22 rivers) during various intervals of historical time. Our conclusions concerning some of these may be somewhat unjustified, but for an over whelming majority of the objects these conclusions are backed up by quite adequate factual evidence.

A great number of facts indicate that, at least during the last 4500 years, periodic planet-wide rearrangements of the drainage system have taken place. Accordingly, water bodies and streams have tended to shift toward the equator during cold periods and toward the poles during warm periods. There is only one possible explanation of this correlation between the changes in the drainage system and the fluctuations in climate: the correlation must exist due to corresponding fluctuations in the Earth's angular velocity, caused by climatically induced redistributions of the water mass on the Earth's surface. The redistributions take place in a meridional direction, parallel to the diurnal-rotation axis of the planet.