Archaeology and climate: Settlement and lake‐level changes at the Aral Sea

Abstract

New archaeological and geomorphologic data collected adjacent to the Aral Sea show lake-level stands during the late Pleistocene and the past 5000 years. On the northern and southern shores, archaeological sites from the Palaeolithic through the Late Middle Ages contain evidence of various cultures and economies. Changes in settlement activity during the mid-Holocene are related to several major lake-level oscillations. Some of them, especially those which occurred at approximately 350-450 cal B.P. (during the Little Ice Age), 700-780 cal B.P., around 1400 cal B.P., and 1600-2000 cal B.P., were accompanied by lithological changes in sediment cores retrieved from the Aral Sea and were observed in shoreline shifts. We show that a maximum lake level at 72-73 m above sea level cannot be corroborated. The highest lake level, which was reached at the beginning of the 20th century, probably never exceeded 54-55 m a.s.l. Furthermore, we documented a previously unknown low-level stand at 42-43 m a.s.l. that dated to the Bronze Age (~4000-3000 B.P.). The regression during 1200-1300 cal A.D. was formerly underestimated and was lower than the present-day lake level. The observed environmental changes, except those since the 1960s, are most probably driven by climate variability, though human activities (e.g., irrigation) can amplify the impact.

River inflow and salinity changes in the Caspian Sea during the last 5500 years

“…In the Holocene, the Aral Sea and Lake Van (eastern Turkey) show a humid climate or high lake levels until c. 4000 cal. yr ago (Boroffka et al, 2006;Wick et al, 2003) that could correspond to the first period of river inflow and lower salinities of core CP14.…”

“…The periods of river input and lower salinities are most likely to correspond to a cooler regional climate with abundant meltwater inflow. A direct link between the CS record and Eurasian climate (Aral Sea: Boroffka et al, 2006; southern Russia and northern Kazakhstan: Kremenetski et al 1997 andIssyk-Kul: Ricketts et al, 2001; lake Van: Wick et al, 2003) is not straightforward as regional effects (glacier melting, river re-routing or drying) are superimposed onto the Eurasian climate signal. In the Holocene, the Aral Sea and Lake Van (eastern Turkey) show a humid climate or high lake levels until c. 4000 cal.…”

Irrigation in the Khorezm oasis, past and present: a political ecology perspective

“…Over the last two decades, scientists have become increasingly aware that the Aral Sea has also had significant changes in water volume during this same time, and they have made numerous attempts to align the archaeological and environmental data sets to determine whether irrigation caused Aral Sea recessions in the ancient past in ways similar to today (Boomer et al 2000(Boomer et al , 2009Boroffka 2010;Boroffka et al 2005Boroffka et al , 2006Cretaux et al 2013;Letolle et al 2007;Maev et al 1991;Oberhansli et al 2007;Reinhardt et al 2008;Sorrel et al 2006Sorrel et al , 2007. A problem arises, however, because these studies assume that the same human causes underlie historically separate events of environmental change; that is, they assume that Khorezm's irrigation systems have always been designed to maximize the use of water resources for intensive agriculture at the expense of the natural environment.…”

Irrigation in the Khorezm oasis, past and present: a political ecology perspective

“…Over the last two decades, scientists have become increasingly aware that the Aral Sea has also had significant changes in water volume during this same time, and they have made numerous attempts to align the archaeological and environmental data sets to determine whether irrigation caused Aral Sea recessions in the ancient past in ways similar to today (Boomer et al 2000(Boomer et al , 2009Boroffka 2010;Boroffka et al 2005Boroffka et al , 2006Cretaux et al 2013;Letolle et al 2007;Maev et al 1991;Oberhansli et al 2007;Reinhardt et al 2008;Sorrel et al 2006Sorrel et al , 2007. A problem arises, however, because these studies assume that the same human causes underlie historically separate events of environmental change; that is, they assume that Khorezm's irrigation systems have always been designed to maximize the use of water resources for intensive agriculture at the expense of the natural environment.…”