The Black and Caspian Seas. Studies of fluctuations in the levels of the Black and Caspian Seas during the Holocene led Fedorov and Skiba (1960) to the following conclusions. Transgressions of the Black Sea (the Neoeuxine, Nymphaic,* and Recent transgressions, at any rate) coincide with dry, warm periods, whereas regressions coincide with wet, cool periods. Transgressions of the Caspian (Neo-Caspian, at most Neo Caspian and late Neo-Caspian), on the other hand, take place during wet, cool periods, while regressions of the Caspian correspond to dry, warm periods. Thus, transgressions of the Black Sea correspond to regressions of the Caspian, and vice versa.
In connection with the foregoing conclusions of Fedorov and Skiba, we should add the following. We decided long ago that the fluctuations in the levels of the Azov-Black and Caspian Seas over the centuries (at least during the last 4500 years) were asynchronous, and that these fluctuations correlate very closely with Shnitnikov's curve for the long-term variability of the wetness of the Northern Hemisphere during this same period. We reported this conclusion in April 1960 at a meeting of the Geology Section of the Conference on the Caspian Problem, held by the USSR Academy of Sciences in Moscow. At this conference it was noted, in particular, that it is impossible to explain completely all the observed regularities in the level fluctuations of the Azov-Black and Caspian Seas in terms of solely eustatic variations (for the Azov-Black Sea basin) and in terms of variations in the precipitation-evaporation balance (for the Caspian). Moreover, it is impossible to explain these regularities even if we take into account tectonic movements. For example, how can we explain the fact that during the present period the level of the Azov-Black Sea water is rising twice or three times as fast as the level in the ocean at the same latitudes? Also, how is it possible to account for the difference between the long-term fluctuations in the level of the Caspian in the south (around Baku) and the fluctuations in the north (around Astrakhan) ? A satisfactory explanation of all the observed regularities in the level variations of these bodies is possible only if we take into account the long-period fluctuations (over the centuries) in the diurnal-rotation regime of the Earth, produced [as noted above] by the rearrangements of the water mass on the Earth's surface which accompany climatic fluctuations. The observed regularities in the level fluctuations of these water bodies are probably, to a large extent, a particular manifestation of a more general regularity in the evolution of the Earth. This more general variation is the periodic (synchronous with climatic fluctuations, and thus with fluctuations in the Earth's diurnal-rotation regime) rearrangement of the drainage system on a planet-wide scale, inwhichthe rivers andwater bodies are oriented (shifted) sometimes poleward and sometimes equatorward.
It is important to note the following: numerous geological, archaeolo gical, and historical data give incontestable evidence that during the last 4500 to 5000 years the level of the Azov-Black Sea water began to drop with the onset of each of the three cold periods and began to rise with the onset of each of the three warm periods (present period included). The main reason for this phenomenon, apart from eustatics, is that the centrifugal forces of the Earth's diurnal rotation vary as a result of climatic fluctuations.
The level of the Caspian, on the other hand, began to rise with the onset of each cold period and began to drop with the onset of each warm period (present one included). The fact that the level fluctuations in the northern and southern Caspian are not coordinated with one another is especially noteworthy.
The variations in the volume of the Caspian, and also the uncoordination of the level variations in its northern and southern parts, can be explained as follows. The level of this sea is determined not only by the ratio between precipitation and evaporation but also by the diurnal-rotation regime of the Earth.* Let us assume, for example, that the angular velocity of the Earth is constant in magnitude. In this case the level of the sea will clearly depend mainly on the evaporation rate and on the amount of precipitation falling into its basin. Thus the fluctuations in water level will be the same in all parts of the sea, that is, they will be of the same magnitude and will take place at the same time.
Now let us assume that the amounts of evaporation and rainfall in the sea basin are constant and that the rotational regime of the Earth varies. In such a case we have two possibilities. First, if the diurnal-rotation velocity starts to increase, all the water (both surface and subsurface) in the Aral-Caspian depression tends to shift toward the equator under the influence of the centrifugal forces. In conformity with the geomorphological features of the locality, this water moves toward the southeastern part of the depression (the Caspian basin); in particular, the flows of such rivers as the Amu Dar'ya and Syr Dar'ya will deviate in this direction. As a result, the sea level will rise in this area, since the influx of water from the south re mains practically the same while the influx from the north (and especially from the northeast) increases sharply. Consequently, the level of the Caspian rises and the level of the Aral drops correspondingly, just as a result of the redistribution of the water masses of the Aral-Caspian basin caused by an increase in the rotational velocity of the Earth. It is significant that the water level in the southern part of the sea will rise somewhat higher than the level in the northern part.