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The ongoing changes affecting Lake Urmia (NW Iran) are revealed by the lake water level decrease (~7 m in the last 20 yr) that was attributed to natural and anthropogenic causes but the exact impact of these factors on the state of the lake is still not identified. Indeed, lack of detailed record of environmental evolution of the lake in the past limits the understanding of actual and future processes. Our project aims to obtain a high-temporal resolution record of environmental changes in the lake area for the last ~30 kyrs. Sediment cores have been obtained from the recently dried out part of the lake near Urmia City, and surface and ground waters have been measured for electric conductivity. This paper presents results of water and sediments analyses. Six 14C AMS dating on organic fractions provide a chronological framework and indicate that the record covers the last ~30 cal kyr BP. During this period, evaporitic conditions were prevailing in the lake. The electric conductivity of brines from the sediment highlights changes in the lake water salinity. The data indicate a lake-level low stand at ~30 cal kyr BP that was followed by a water level rise and establishment of lacustrine conditions for the next ~9 kyr, this phase representing the highest lake level recorded since that time to date. From the LGM, the lake experienced several fluctuations of the water level. The relatively long-term lacustrine condition established during the Early Holocene before the water level decrease between ~5.5 and 4.9 cal kyr BP. Sediments from the two dry events at ~30 cal kyr BP and at 5.5–4.9 cal kyr BP are characterized by the presence of greigite, which indicates anaerobic early diagenetic conditions in the sediment. [ABSTRACT FROM AUTHOR]

We analyzed by high resolution X-ray fluorescence core scanning (XRF-CS) the elemental composition of a 12.5 m long composite sediment core extracted from the hypersaline Lake Urmia (NW Iran). The main objective of the study was to reconstruct on a high temporal scale, the changes in sediment origin/inflow and water levels of Lake Urmia over the last 30,000 years. Combined with previously obtained results on 14C accelerated mass spectrometry (AMS) chronology, grain size and distribution of major minerals, albeit with a much lower temporal resolution than the XRF-CS data, this multi-proxy approach allowed recognition of specific hydrological changes and associated sedimentary processes in the Lake Urmia basin, including physical and chemical weathering, depositional fluxes and carbonate crystallization processes in lake water, and early diagenesis in anoxic bottom sediments. The high natural logarithm ratios (ln-ratios) of K/Ti, Ca/Ti and Sr/Ca, and low ln-ratios of Rb/Sr reveal increasing chemical weathering in the catchment area in conjunction with increasing authigenic carbonate precipitation in the lake. These findings reflect wet conditions, high lake levels and less saline water during the following intervals (i) 29.8–20.2, (ii) 15.2–13.3, (iii) 11.8–5.6 and (iv) 4.1–2.3 cal kBP. In contrast, the increasing ln-ratios of Rb/Sr associated with decreasing ln-ratios of K/Ti, Ca/Ti and Sr/Ca indicates enhanced erosion in the catchment area linked to drier conditions, lower lake levels and more saline conditions predominating at around 30–29.8 cal kBP, 20.2–15.2, 13.3–11.8, and 5.6–4.1 cal kBP. Based on the As-XRF-CS pattern and magnetic parameters we identified iron and naturally-occurring arsenic sulfides rarely reported from saline lakes, acting as specific indicators of anoxic conditions in the lake bottom environment. Moreover, XRF-CS data revealed short-lived periods with increasing chemical weathering in the catchment area at (i) 28.6–28.3, (ii) 27.3–27.1, (iii) 4.1–3.6 and (iv) 3.4–3.3 cal kBP, as well as increasing erosion at (i) 27.0–26.8, (ii) 26.3–26.0, (iii) 25.6–25.3 and (iv) 24.6–24.4 cal kBP. Overall, this study confirms the previously reported findings concerning the sediments of Lake Urmia as well as completing these, both by providing more details on the environment for the periods already identified and by highlighting events of short duration. In particular, the results reported here permit better definition of the processes of chemical weathering versus erosion in the catchment area, and of the oxygenation levels of the lake bottom. The close correlation of these long- and short-term changes with the North Atlantic climate system clearly indicates that the Lake Urmia area has been affected mainly by this system during the last 30 cal kBP. Over and above their value with regard to Lake Urmia, these new data fill an important gap in eastern Mediterranean/western Asia paleoclimate records as a whole, providing unique and continuous 30 cal kBP information on the possible driving mechanisms of the observed changes. These can be compared to existing data on paleoenvironmental and climatic changes on regional and global scales and can also be used in global circulation models. [Display omitted] • Last 30 kyr lake evolution; wet LGM and Early Holocene, dry Mid to Late Holocene. • Erosion/chemical weathering in the catchment and carbonate crystallization in the lake. • Arsenic of natural origin and iron sulfides show anoxic depositional conditions. • Short-term climate variations correlated to Dansgaard-Oeshger events 4 and 3. • Last 30 kyrs of long and short term climate change related to North Atlantic system. [ABSTRACT FROM AUTHOR]