Journal: Scientific Reports

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

doi: 10.1038/s41598-017-00371-w

Figure Lengend Snippet: Salinity profile measured in the pore water of Lake Van. The porewater salinity was measured in core-catcher samples during ICDP PaleoVan drilling operations in 2010 (left-hand panel, black dots). The area shaded gray marks the depth range characterized by lower salinities that might correspond to past freshwater stages of Lake Van , . Modeling the physical transport of salt through the sediment pore space (left-hand panel, red line and dashed blue line) shows that the salinity changes in the uppermost 100 m can be reproduced reasonably well either using the reconstructed (right-hand panel, red line) or synthetic (right-hand panel, dashed blue line) salinity curve as a temporal boundary condition at the sediment/water interface. The areas shaded red and blue in the left-hand panel represent the variation range of the model results depending on the molecular diffusivities of the various ions contributing to the overall salinity. Between 83 and 135 ka BP (MIS5), and between 215 and 248 ka BP (MIS7), the synthetic input curve implies the export of salt from Lake Van through an outflow.

Article Snippet: Pore water for the salinity measurements was extracted from the bulk sediment with a GEOTEK porewater squeezer ( http://www.geotek.co.uk ) and filtered through a glass-fiber prefilter (Sartorius, Item No. 13400–100, diameter 100 mm) and a hydrophilic polyethersulfone membrane (VWR, Item No. 514–4233, pore size 0.45 μm, diameter 25 mm). pH was determined in the field simultaneously to the salinity measurements using a portable pH meter (Metrohm Model 704).

Techniques:

Journal: Scientific Reports

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

doi: 10.1038/s41598-017-00371-w

Figure Lengend Snippet: Salinity, Na + , Cl − , alkalinity, and pH profiles measured in the pore water of Lake Van. All measurements were conducted in the pore water of the same core-catcher samples used for the determination of salinity. The curves of the conservative species Na + (panel B, red circles) and Cl − (panel B, blue triangles), as well as that of alkalinity (panel B, black squares), mimic the shape of the salinity profile (panel A; see also Fig. ). The linear correlations that exist between salinity and both Na + and Cl − (panel D, red circles/line and blue triangles/line) demonstrate that total salinity in Lake Van is virtually geochemically conservative and can thus be used as a conservative tracer for reconstructing lake levels. The linear correlation between salinity and alkalinity (panel D, black squares/line) indicates the presence of stable hydrochemical conditions over the time span relevant for the inferred lake-level changes. The gray symbols indicate measurements conducted in porewater samples with lower salinities that might represent a relict of Lake Van's earlier, freshwater, stage , ; these measurements were therefore excluded from the calculation of the least squares regressions in panel D. The mean pH value for the time span relevant for the lake-level reconstruction is 9.1 ± 0.3 (calculated using the data plotted as black circles in panel C). This rather constant pH again suggests that the composition of the dissolved species in the water body of Lake Van was rather stable. A slight drop in pH observed at 32 m (approximately 86 ka BP) coincides with a water outflow (“open condition”) exporting salt from the lake during MIS5. A major decrease in pH below 170 m (gray circles) seems to result from the entrapment of “paleowater” from the time when the basin of Lake Van was not yet closed and operated as a freshwater system.

Article Snippet: Pore water for the salinity measurements was extracted from the bulk sediment with a GEOTEK porewater squeezer ( http://www.geotek.co.uk ) and filtered through a glass-fiber prefilter (Sartorius, Item No. 13400–100, diameter 100 mm) and a hydrophilic polyethersulfone membrane (VWR, Item No. 514–4233, pore size 0.45 μm, diameter 25 mm). pH was determined in the field simultaneously to the salinity measurements using a portable pH meter (Metrohm Model 704).

Techniques: