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oxygen 18 composition a palaeo-climate indicator and the ECM records wcre found to bc synchronous, which shows that the ECM is related to climate changes. Layers with heavier oxygen-l 8 compositions, which correspond to warmer climates show also highcr ECM values, which is an evidence of lower dust content. The fluctuations in the ice conductivities were found to be abrupt, which means that conditions of dust transport also changed abruptly. This means that the periods of climate change were also periods of rapid changcs in the atmospheric circulation and changes of wind speeds due to changes in the temperaturę gradients between high and mid northern latitudes.

L.A. Scuderi (1990) correlated tree-ring variations in the Sierra Nevada and the sulfur rich aerosols recorded in the Greenland ice cores on the dec-adal level. The good correlation brought him to the conclusion that indeed volcanic eruptions are significant forcing mechanism on the time scalę of tens to hundreds of years of climate changes. He maintains that while single vol-canic events may only lead to short colder periods a cluster of significant events may lead to glaciation.

4. THE COMBINED MECHANISM - VOLCANISM AND DUST

STORMS

These observations has brought the present author to suggest that indeed yolcanic activity was an important if not major cause for the periods of cold climates during the Holocene (Issar 2003). In other words, if one assumes that due to the Milankovitch cycles the Holocene is a post glacial and thus a warm period, then one needs a cooling mechanism for the discontinuation of the steady State warm phase. Yet, the volcanic dust veil as a cooling mechanism may work only as a very short-term effect but does not answer the long du-ration phenomena lasting for a few centuries to morę than a thousand years. Thus one needs some kind of an additional mechanism that will produce a carbon dioxidc sequestering sink, which will keep the global cooling pro-cess going on for a longer period.

Such a process might occur once the “volcanic effect” is viewed as a trig-gering factor of high-pressure Systems over the Gobi and Sahara deserts, which gencrate dust storms like those which occurrcd during the glacial periods These occurred also during historical periods as shown by the data collected by A. Bucher (1986). He found a correlation between contemporaneous cy-clonic storms entering the Sahara and “red rains” over Southern Europę. Moreover, his survey of Roman and Monastery chronicles brought him to produce a curve of periods of high freąuencies of such events during hi stor-