Browsing by Author "Meydan, Aysegul F."

Now showing 1 - 2 of 2

The Annual Particle Cycle in Lake Van (Turkey)
(Elsevier Science Bv, 2012) Stockhecke, Mona; Anselmetti, Flavio S.; Meydan, Aysegul F.; Odermatt, Daniel; Sturm, Michael
The varved sediments of Lake Van provide a high-quality continental archive of seasonal to decadal-scale climate variability. In order to read the natural record, modern varve formation was studied on the basis of (1) remotely-sensed total suspended-matter (TSMrs) concentrations; (2) time-series of particle flux and water temperatures; and (3) turbidity, temperature, and oxygen profiles. TSMrs, validated by contemporaneous water-column sampling, shows great temporal and lateral variations (whitings and turbidity plumes). From 2006 to 2009, sequential sediment traps recorded high particle fluxes during spring and fall, medium fluxes during summer, and almost zero flux during winter. The mean total mass flux of 403 mg m(-2) day(-1) comprised 33% (seasonally up to 67%) calcium carbonate, 7% aquatic organic matter, 6% biogenic opal, and 54% detrital minerals. The CaCO3 fluxes are controlled by river discharge (precipitation and snowmelt) during spring, by high productivity during summer, and by river discharge (precipitation before snowfall starts) and mixing during fall. In November 2007, an anomalously high CaCO3 flux occurred as a result of a warm water surface supersaturated with calcite coinciding with an anomalous runoff event. The results demonstrate that the couplets of light and dark laminae in the short sediment cores are true varves representing spring-summer-fall and winter conditions, respectively. Consequently, varve formation can be linked to the seasonal climate pattern, providing a calibration that can be used to interpret the partially varved paleo-record of Lake Van and related environmental processes. (C) 2012 Elsevier B.V. All rights reserved.
Noble Gases in the Sediments of Lake Van - Solute Transport and Palaeoenvironmental Reconstruction
(Pergamon-elsevier Science Ltd, 2014) Tomonaga, Yama; Brennwald, Matthias S.; Meydan, Aysegul F.; Kipfer, Rolf
Sediment samples acquired in 2010 from the long cores of the International Continental Scientific Drilling Program (ICDP) PaleoVan drilling project on Lake Van for noble-gas analysis in the pore water allow determination of the local terrestrial He-gradient as a function of depth within a sediment column of more than 200 m. These measurements yield first insights into the physical transport mechanisms of terrigenic He through the uppermost part of unconsolidated lacustrine sediments overlying the continental crust. In line with our previous work on the spatial distribution of the terrigenic He release into Lake Van, we identify a high He concentration gradient in the uppermost 10 m of the sediment column. The He concentration gradient decreases below this depth down to approx. 160 m following in general the expectations of the modelling of radiogenic He production and transport in a sediment column with homogeneous fluid transport properties. Overall the in-situ radiogenic He production due to the decay of U and Th in the mineral phases of the sediments accounts for about 80% of the He accumulation. At approx. 190 m we observe a very high He concentration immediately below a large lithological unit characterised by strong deformations. We speculate that this local enrichment is the result of the lower effective diffusivities in the pore space that relate to the abrupt depositional history of this deformed unit. This particular lithological unit seems to act as a barrier that limits the transport of solutes in the pore space and hence might "trap" information on the past geochemical conditions in the pore water of Lake Van. The dissolved concentrations of atmospheric noble gases in the pore waters of the ICDP PaleoVan cores are used to geochemically reconstruct salinity on the time scale of 0-55 ka BP. Higher salinities in the pore water at a depth of about 20 m suggest a significantly lower lake level of Lake Van in the past. (C) 2014 Elsevier Ltd. All rights reserved.