Long-term freshening of the Dead Sea brine revealed by porewater Cl− and in ICDP Dead Sea deep-drill
Introduction
The lakes that filled the tectonic depression of the Dead Sea basin during the late Quaternary comprise mixtures of Ca-chloride brines that evolved from the late Neogene Sedom Lagoon and freshwater from the lake watershed (e.g. Neev and Emery, 1967, Stein, 2001). The Ca-chloride brine within the lake evolved further by mixing with inflowing brine springs and by deposition or dissolution of evaporitic minerals (e.g. aragonite, gypsum and halite). This, in turns reflects the prevailing limnological–hydrological conditions in the Dead Sea basin and its watershed (Stein et al., 1997; Stein, 2001; Gavrieli and Stein, 2006, Katz and Starinsky, 2009).
So far, most of the information on the evolution of the lakes was derived from the mineralogical and geochemical properties of the sediments recovered from exposures of the marginal terraces or shallow drillings along the lake's shores (Fig. 1). The sediments studied in these sequences consist mainly of the primary (evaporitic) minerals, aragonite and gypsum and fine-grained detritus (Katz et al., 1977, Kolodny et al., 2005, Migowski et al., 2006; Stein et al., 1997, Stein et al., 2010; Torfstein et al., 2005, Torfstein et al., 2008; Haliva-Cohen et al., 2012). The drilling project that was conducted under the wings of ICDP (International Continental Scientific Drilling Program) recovered a detailed core from the deep part of the Dead Sea (ICDP Site A, Fig. 1, Stein et al., 2011) providing a unique opportunity to study the solution history of the deep parts of the lake (i.e. the hypolimnion) by direct analyses of the chemical and isotopic composition of porewater brines.
This paper describes the results of chloride (Cl−) and oxygen isotopes () analyses of pore fluids that were extracted from the deep central lake core (Site A, Fig. 1) during the drilling operation. The objective of the study was to reconstruct the limnological and geochemical properties of the deepest part of the lake and establish the mechanism that controlled lake configuration and salinity during the studied time interval. The paper focuses on the time interval of past 70 ka BP during which the tectonic depression of the Dead Sea basin was occupied by the last glacial Lake Lisan and the Holocene Dead Sea (e.g. Haase-Schramm et al., 2004, Migowski et al., 2006, Stein et al., 2010).
Section snippets
Geological settings
During the Neogene–Quaternary times a series of water-bodies filled the tectonic depressions along the DS rift. The history of these water-bodies commenced with the ingression of the late Neogene Sedom lagoon and continued after the disconnection of the lagoon from the open sea with the development of lakes succession that included the hypersaline mid to late Pleistocene Lake Amora, the last interglacial Lake Samra, the glacial Lake Lisan and the Holocene Dead Sea and the freshwater lakes
Sampling
During the ICDP–Dead Sea drilling project sediments cores were recovered from the center of the lake (Site A, Fig. 1) at water depth of 300 m. The drilling reached 460 m below the lake floor and the recovered cores were preliminary described on board.
The drilled-cores were sectioned into 1.5 m slices and kept in a dark refrigerated repository. Preliminary description and analyses of the sediments in all sections were conducted during 2012 by all members of the Dead Sea Deep Core consortium in
General description of the studied sequence in the core
This paper focuses on the last glacial and post-glacial period, the upper 190 m out of the total 460 m drilled core (a simplified stratigraphic description provided in Fig. 2). The sediments composing this part of the core are mainly detrital silt-size calcite and quartz grains, primary aragonite gypsum and halites (Stein et al., 2011, Neubereger et al., 2012). The sediments comprise several sedimentary facies (e.g. Machlus et al., 2000): (1) Sequences of laminated of aragonite and
Limnological configuration of Lake Lisan
The studies in the Dead Sea area on the exposed onshore terraces show that during most of the last glacial period (), when Lake Lisan reached high stand of (Bartov et al., 2003, Torfstein et al., 2013) the lake was stratified, depositing the aad facies, the annual and seasonal laminated sequences of primary aragonite and silty-detritus material (Katz et al., 1977, Stein et al., 1997). The primary aragonite was deposited from the epilimnion that was supplied with
Summary
The pore brine data presented here provides the first direct measurement of the composition of the deep brine (hypolimnion) of the Dead Sea lakes during the late Pleistocene and Holocene periods (). Specifically, pore brine profiles suggest that during the Lisan period, Cl− concentration of the hypolimnion decreased down to at least 70% of the modern Dead Sea value and value was (almost 3‰ higher than modern).
The freshening of the last glacial Lake Lisan was accompanied by
Acknowledgments
This study results from the ICDP Dead Sea drilling project. We thank all who participated in the drilling operations, opening and descriptions of the drilled cores. The scientific study is supported by an Excellence Center grant of the Israel Science Foundation (ISF) grant 1736/11 to B.L. (The Dead Sea Deep Drilling Project: The Dead Sea as a Global Late Quaternary Paleo-Environmental, Tectonic, and Seismological Archive). We thank Joris Gieskes for his thorough review that helped in improving
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Constraints on aragonite precipitation in the Dead Sea from geochemical measurements of flood plumes
2019, Quaternary Science ReviewsCitation Excerpt :Based on radiocarbon data Stein et al. (2013) described a model of “turbulent mixing” on the interface between the upper less saline water-body (epilimnion) and the lower brine (hypolimnion) filling the lake. The epilimnion/hypolimnion turbulent mixing model was also applied to explain the variations in the concentrations of Br−, and Cl− in the pore waters extracted from the sediments drilled at the deep floor of the lake by the ICDP (Lazar et al., 2014). However, not all the factors controlling aragonite precipitation in the DS lakes are fully understood.