Evaluating abiotic and microbial factors on carbonate precipitation in Lake Acig-ol, a hypersaline lake in Southwestern Turkey Nurgul Balci a, * , Cansu Demirel a , Sena Akcer € On b , A. Haydar Gültekin a , Mehmet Ali Kurt c a Department of Geological Engineering, Istanbul Technical University, Istanbul, Turkey b Mu gla Sıtkı Kocman University, Faculty of Engineering, Department of Geological Engineering, Mu gla, Turkey c Advanced Technology Education, Research and Application Center, Mersin University, 33358, Mersin, Turkey article info Article history: Received 12 September 2017 Received in revised form 19 December 2017 Accepted 26 December 2017 Available online xxx Keywords: Lake Acıg€ ol Hypersaline Carbonates Microbial processes Isotopes abstract The recent carbonate precipitation occurs in Lake Acıg€ ol, a hypersaline playa lake. Elucidating precipi- tation mechanisms of carbonate minerals under particularly supersaturated ionic solution at low tem- perature may hold key understanding to recognize microbial fingerprints throughout the Earth history. In the presented study abiotic and microbial factors controlling carbonate precipitation mechanisms are investigated by using geochemical, isotopic and chemical approaches. Our data demonstrated that aragonite, calcite and dolomite are readily precipitated in oxic column of lake water in decreasing order. Major metabolites profile of pore water showed that carbonate alkalinity and pH increased by microbial activity seems to be insignificant in the lake sediments to support precipitation. On the contrary a positive correlation between d 13 C and d 18 O values of carbonates suggest that carbonate super-saturation occurs as a result of evaporation and associated degassing of CO 2 in the lake basin. However, a putative microbial role such as binding of cations to microbial cell wall or EPS to overcome kinetic inhibitors (e.g Mg 2þ ) is likely possible in the lake as a driving carbonate precipitation mechanism. Overall, the present study demonstrated that carbonate precipitation in the lake is the result of complex players, such as lake water chemistry, ionic interactions, evaporation and EPS-organic compounds (e.g EPS) in addition to kinetic microbial processes. The data also provide a fundamental insight which is that revealing of changes in carbonate mineralogy of the lake, strongly influenced by evaporation, would provide sig- nificant insights about paleoclimatic conditions of the region. © 2017 Elsevier Ltd and INQUA. All rights reserved. 1. Introduction Carbon cycle is intimately linked with the other major geochemical cycles such as S, N and P in marine and non-marine settings. The formation of carbonate minerals in geochemically diverse settings can be very complex involving evaporation, dissolution-re-precipitation, degassing of CO 2 in addition to mi- crobial processes (Thompson and Ferris, 1990; Thompson et al., 1997; Warthmann et al., 2000; Wright and Oren, 2005; Forti, 2005; Balci, 2010; Meisteret al., 2011a, 2011b; 2013; Kaplan et al., 2013; Balci et al., 2016; Balci and Demirel, 2016; Eren et al., 2016). Elucidating of carbonate precipitation mechanism has been a subject of numerous research for the last few decades with a special interest to microbial processes (Castanier et al., 1999; Van Lith et al., 2003, Braissant et al., 2003; S anchez-Rom an et al., 2009, 2011; Bontognali et al., 2010). Such processes profoundly contributed to carbonate production throughout the Earth's history (Grotzinger and Knoll, 1999; Thompson et al., 1997; Reid et al., 2000) In particular, demonstration of dolomite precipitation with microbial culture, kinetically inhibited at low temperature, has brought new interpretations for carbonate formation environments (Friedman and Sanders, 1967; Kenward et al., 2009; Krause et al., 2012). Later on experiments carried with different microbial species, particularly with sulfate reducing bacteria (SRB), suggest a micro- bial factor involved in carbonate precipitation, particularly dolo- mite (Roberts et al., 2004; Vasconcelos and McKenzie, 1997; Vasconcelos et al., 1995). Numerous laboratory and field studies has been carried out to elucidate the role of microorganisms in the precipitation of * Corresponding author. ITU Faculty of Mines, Department of Geological Engi- neering, Ayazaga Campus, 34469, Maslak, Istanbul, Turkey. E-mail address: ncelik@itu.edu.tr (N. Balci). Contents lists available at ScienceDirect Quaternary International journal homepage: www.elsevier.com/locate/quaint https://doi.org/10.1016/j.quaint.2017.12.046 1040-6182/© 2017 Elsevier Ltd and INQUA. All rights reserved. Quaternary International xxx (2017) 1e13 Please cite this article in press as: Balci, N., et al., Evaluating abiotic and microbial factors on carbonate precipitation in Lake Acig-ol, a hypersaline lake in Southwestern Turkey, Quaternary International (2017), https://doi.org/10.1016/j.quaint.2017.12.046