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M.B. Aberlin (1996) to be due to the fact that it contains iron oxide, which is a fertilizing agent. This causes a bloom of the phyto-plankton the fixing of carbon dioxide and its reduction in the atmosphere. Indeed iron was found to be the limiting nutrient in the central Pacific Ocean and dust from the Gobi desert in China has been shown to induce productivity increases near Hawaii. Experiments of spreading iron containing fertilizers conducted near the Galapagos Islands induced phytoplankton blooms (Watson et al. 2000).

2. CLIMATE CHANGE FORCING MECHANISMS DURING THE HOLOCENE

While the Milankovitch forcing mechanism coupled with dust storms pro-videst an explanation to the mechanism causing climate changes during the Pleistocene, when it comes to the Holocene, its periodicity of changes, last-ing only a few centuries (maximum a millennium) and even a few decades, the ąuestion of mechanism is still debated.

J.E. Kutzbach and F.A. Street-Perrott (1985) still maintain that the Milank-ovitch forcing mechanism was responsible for the climate changes, which affected the lakę levels in the Northern Hemisphere, tropics and subtropics sińce the Last Glaciation. They claim to have arrived at a good correlation between an atmospheric general-circulation model (GCM), simulating the climates of January and July at 3,000 years intervals, and the evidence regard-ing palaeo-levels in the Northern Hemisphere tropics and sub tropics. Both model and observations show high levels between 6,000 and 9,000 BP. How-ever, Kutzbach and Street Perrott admit that the response of the monsoon system to the amplified seasonal cycle of solar radiation as a function of the variations in earth*s orbit, are phenomena, which occur on a too long time scalę to account for the millennia, not to speak on the century, long ciimatic changes.

F.A. Street-Perrott and R.A. Perrott (1990) found a correlation between the droughts in the Sahel and tropical Mexico sińce 14,000 years ago and the injections of fresh water into the northem part of the North Atlantic. The decrease in salinity reduces the formation of North Atlantic Deep Water cir-culation, which is an important factor in the regulation of the global oceanie circulation. This results in the cooling and a change in the distribution of sea surface temperatures, affecting the rainfall in the northem tropics. Still the reasons for the fresh water injection phenomena are not yet elear.

W. Dansgaard et al. (1984) claim that there exists a quasi periodicity of 2550 years in the oxygen-18 oscillations of the deep Greenland ice cores, which brought them to the conclusion that the forcing of these cycles is eon-