Depositional environments and salt-thickness variations in Urmia Lake (NW Iran): Insight from sediment-core studies

Abstract

Urmia Lake is a large-scale hypersaline lake that experienced a drastic water-level fall due to natural and anthropogenic forces during the last two decades. Construction of a causeway in the central part of the lake after 1989 has divided the lake into northern and southern parts and caused an extreme change of the lake hydrochemical system. Precipitation of evaporite minerals as crust on the lake floor was caused by the combination of lake level fall and increasing water salinity. However, some parameters controlling rates of salt deposition and dissolution and temporal and spatial variation in salt thickness in Lake Urmia are poorly understood. This study reviews 90 sediment cores from various parts of the lake to put forward a better understanding of the salt depositional system and salt thickness variations in the basin for the last 40 years (1977–2017). Our results indicate that the sedimentary system of Urmia Lake changed rapidly during the last two decades from a permanent hypersaline lake with predominantly fast terrigenous–biochemical sedimentation to a seasonally changing playa sedimentary environment with predominance of evaporite minerals. These changes are responsible for rapid salt deposition that generated a salt-crust with a maximum thickness of 2.95 m overlying Holocene terrigenous sediments. The salt-crust thickness and the water depth have a positive correlation for water depth greater than 1 meter, which means that salt-crust thickness increases where water depth increases. While the thickness of shallow deposits are affected by fresh-water dissolution. In addition, the average salt precipitation rate in the northern and the southern parts of the lake is 466 and 266 times higher, respectively, than the average (0.3 mm/y) sedimentation rate before the lake shrinkage. Similar to other large hypersaline lakes such as the Great Salt Lake (USA) and the Aral Sea (Central Asia), the manmade intervention at Urmia Lake (damming of the catchment, extension of agricultural fields, and causeway construction in the middle part of the lake) threatens its further hydrologic existence.

Landscape evolution in orogenic plateaus: Insights from quantitative morphotectonic analysis of the Turkish–Iranian Plateau and Caucasus regions

“…in the east (Figure 1a), with a range of annual precipitation from 300 to 700 mm (Hijmans et al, 2005; Kehl, 2009; Figure 1b). The present‐day climate is arid to semi‐arid with a strong seasonality in precipitation including wet winters and dry summers (e.g., Djamali et al, 2009; Mohammadi et al, 2021; Sharifi et al, 2015). The heterogeneous distribution of precipitation across the TIP is caused by the orographic barriers of the Pontides, Bitlis, Zagros, and Alborz mountains preventing moist air from the Black Sea, Mediterranean Sea, and Caspian Sea from entering the plateau interior (Figure 1a; Agard et al, 2011; Ballato et al, 2010; Meijers et al, 2018).…”

Sedimentary evolution and lake level fluctuations of Urmia Lake (north‐west Iran) over the past 50 000 years; insights from Artemia faecal pellet records

“…Positions of previously dated sediment cores are also shown; Urmia 20 (Kelts & Shahrabi, 1986), BH2 (Djamali et al, 2008;Stevens et al, 2012), UBA (Manaffar et al, 2011), SK1D (Talebi et al, 2016), UL6, UL7 (Sharifi, 2017), G5, G6, G7 (Tudryn et al, 2021), G6, G7 (Kong et al, 2022). The lake map was modified from Mohammadi et al (2021).…”

“…Hypersaline ecosystems have semi-arid/arid climates, high dissolved ion concentrations, alkaline water and low nutrient availability, and are thus considered exceptional natural laboratories. These ecosystems have been studied for reconstructing changes in their physicochemical, sedimentological and biological properties (Williams & Liebhold, 2002;Alipour, 2006;Oren, 2009;Lak et al, 2011Lak et al, , 2012Lak et al, , 2022Gajardo & Red ón, 2019;Mohammadi et al, 2021Mohammadi et al, , 2023.…”

“…On the other hand, Artemia salina faecal pellets at the tropholytic zone in Techirghiol Lake (Romania) serve as a reliable criterion for the precipitation of high-magnesian calcite inside faecal pellets via bacterial metabolism (Baltres & Medes ¸san, 1978). Artemia has effects on the lake water geochemistry by absorbing calcium and magnesium cations and carbonate anions from the lake water and defecates them as faecal pellets, which causes the depletion of lake water from the aforementioned ions and reduces the chemical deposition of carbonate in the lake (Mohammadi et al, 2021). Similarly, Artemia controls the mineralogy and sedimentation pattern with dominant biochemical deposits in Urmia Lake (e.g.…”

“…Similarly, Artemia controls the mineralogy and sedimentation pattern with dominant biochemical deposits in Urmia Lake (e.g. Kelts & Shahrabi, 1986;Djamali et al, 2010;Stevens et al, 2012;Mohammadi et al, 2021).…”