Porewater salinity reveals past lake-level changes in Lake Van, the Earth’s largest soda lake

Abstract

In closed-basin lakes, sediment porewater salinity can potentially be used as a conservative tracer to reconstruct past fluctuations in lake level. However, until now, porewater salinity profiles did not allow quantitative estimates of past lake-level changes because, in contrast to the oceans, significant salinity changes (e.g., local concentration minima and maxima) had never been observed in lacustrine sediments. Here we show that the salinity measured in the sediment pore water of Lake Van (Turkey) allows straightforward reconstruction of two major transgressions and a major regression that occurred during the last 250 ka. We observed strong changes in the vertical salinity profiles of the pore water of the uppermost 100 m of the sediments in Lake Van. As the salinity balance of Lake Van is almost at steady-state, these salinity changes indicate major lake-level changes in the past. In line with previous studies on lake terraces and with seismic and sedimentological surveys, we identify two major transgressions of up to +105 m with respect to the current lake level at about 135 ka BP and 248 ka BP starting at the onset of the two previous interglacials (MIS5e and MIS7), and a major regression of about −200 m at about 30 ka BP during the last ice age.

Analysis of a fragmentary diatom record from Lake Van (Turkey) reveals substantial lake-level variability during previous interglacials MIS7 and MIS5e

“…3; Kwiecien et al 2014). So perhaps here the lake is at its freshest, with lowest pH, and was hydrologically open Tomonaga et al 2017). At the end of this period, between 126.5 and 126.4 ka BP, C. ocellata dominates the assemblage, with concomitant low N2 values (Fig.…”

“…In terminal lakes such as Lake Van, salinity can be inversely proportional to the volume of the water body (Tomonaga et al 2014(Tomonaga et al , 2017. To estimate past lake volumes (and the respective levels) from the palaeoconductivities (PC) presented in this work we assumed a linear relation between average conductivity (C = 20.2 ± 4.6 mS/cm) and total dissolved solids (TDS = 22.8 ± 0.6 g/kg) determined in water samples collected from Lake Van in 2006.…”

“…These low PSs suggest higher lake levels with respect to the present situation. Tomonaga et al (2017) inferred an open state of Lake Van during MIS7e and MIS5e based on the modelling of salinity of the pore waters. Our lake-level estimations based on the PSs indicate that this was indeed the case: both PSs lie below 13 g/kg representing the salinity at which the lake would exceed the basin threshold located SW at approximately 1749 m a.s.l.…”

“…It should be noted that our first-order estimation of the PSs considers a C value that has been J Paleolimnol (2018) 59:119-133 123 determined using conductivities measured both in the epilimnion and in the hypolimnion, while the rather large uncertainty of C reflects the temperature effect on conductivity. As in Tomonaga et al (2017), we merged a high-resolution digital elevation model (Farr et al 2007) and the bathymetry data for the lake (Turkish Office of Navigation, Hydrography and Oceanography 1990) to obtain a complete three-dimensional representation of the lake basin, which we then used to infer the volume of water necessary to produce the variation in dissolved salt concentration (with respect to the present salinity and volume of Lake Van) that would be necessary to yield the estimated PSs.…”

“…In Lake Van, preserved diatom assemblages are associated with fresh, high lake-level phase, perhaps even an open system (Stockhecke et al 2014b). A recent lake-level reconstruction based on the modelling of pore water salinity reveals that at the onset of two previous interglacials (MIS7 and MIS5) the presence of an outflow fostered freshwater conditions in Lake Van (Tomonaga et al 2017). The primary aim of this study is to provide new insight into Lake Van lake-levels during previous interglacials through the application of diatom analysis.…”