Fluctuations in the Caspian Sea and its impact on the distribution of the last millennium to the third millennium settlement centers in the South East of Caspian Sea

Iranian northern plain is surrounded by the Caspian Sea at North and part of the Alborz Mountains at South. These two geomorphologically distinct features have created unique climatic conditions. A plain lush with abundant rainfall is a result of the proximity of these two distinct geographical regions. As a consequence, the Iranian Northern plain has been in use by human populations since the prehistoric times. The significance of coastal regions for human occupations has been documented all over the world. Abundance of food resources, access to the fresh water (rivers), and having clear landmarks all have made the coastal regions ideal geographical zones for human populations. In addition to that, proximity to the major water sources (big lakes, seas, and oceans) would regulate the climatic changes, and prohibits drastic alternations of the environment. Archaeological data have shown that coastal regions also have been used for human movements through prehistoric and historic times. Repeated exodus out of Africa is among such events. Caspian Sea is the largest lake on earth, and due to its closed drainage basin, has experienced distinctive fluctuations through time. Paleoclimatic data have shown that the minimum water level of the Caspian Sea was -113m and the maximum reached to +50m. During each fluctuation episode vast areas have been revealed and large land resources were revealed or concealed. Archaeological Research at the Southeastern Part of the Caspian Sea. The Southeastern of the Caspian Sea has witnessed archaeological research since the mid twenty century. Since then, numerous archaeological surveys and excavations have been conducted at this region providing clear understanding of the settlement patterns during many archaeological periods. Among such periods, Bronze Age (3rd millennium B.C. to 500 B.C.) has received the most attention by researchers. It has been proven that the Southeastern of the Caspian Sea hosted some of the most well-known Bronze Age archaeological sites in Iran, which among them Gohar Tepe, Yarim Tepe, Shah Tepe, and Tepe Kelar have experienced several archaeological field missions revealing tremendous amount of data concerning the socioeconomic structure of the people during the Bronze Age. What really did take place after this period is relatively unknown since the size and type of the archaeological settlements were drastically decreased. Some have claimed migrations to or out of the region and some have even proposed a clear change in the life style due to the apparent shift in the climatic conditions. Sea Fluctuations at the Southeastern Part of the Caspian Sea and its Impact on the Dispersal of the Archaeological Sites Climatic data indicates that during the Bronze Age, the Caspian Sea level was more or less stable and was -35m. The sea level elevated only 1m during 500 year period, which implies a stable climatic condition. Around 700 A.D. the sea level dropped dramatically to -42m and finally around 1300 A.D. the region witnessed the largest sea advancement (-22.5m). Interestingly enough no archaeological evidence prior to 1300 A.D. has ever reported from the immediate coastal regions and their adjacent areas at the Southeastern of the Caspian Sea. For years, many archaeologists interpreted this gap as an evidence of abounding the region because of some unknown causes. After reviewing the Caspian Sea fluctuations, this paper attempts to reconstruct the coastline at the lowest and highest volatility. Lines needed for this study were calculated using topographic maps and hydrographic basin of the Caspian Sea with the help of the "National Center for Caspian Studies". After preparation of the GIS maps, the greatest regressions were marked on them. The maps show the coastlines at the beginning of 3000 B.C. have been situated far behind the contemporary sea lines. By combining the climatic and archaeological data, this article has shown that in contrast to the former claims concerning the absence of archaeological settlements at the Southeastern of the Caspian Sea, majority of archaeological settlements have been buried under the sediments left by the periodic fluctuations of the Caspian Sea, which among them the 1300 A.D. advancement has had the most effect. This research proposes that all archaeological surveys at the mentioned region must take the sea fluctuations into account prior to the actual field work.