Concentration of the pore water ions and grain size of bottom sediments and subsea permafrost from the Buor-Khaya Bay
This set contains a data on ionic composition of the interstitial water of bottom sediments and subsea permafrost as an indicator of the sedimentation and sea water spreading within thawed strata. Based on measurements of concentration of sodium (Na+), potassium (K+), calcium (Ca2+), and magnesium (Mg2+) cations, chlorides (Cl–) and sulphates (SO42–) in water extracts from bottom sediments and subsea permafrost deposits from three boreholes a spatial difference in salinisation dynamics of thawed strata within the Buor-Khaya Bay was shown. A significant difference between permafrost and unfrozen sections was recorded. The vertical pattern of the macroions in the unfrozen segment was formed under the influence of subsea thawing of permafrost, while the permafrost section was formed under freshwater conditions and evolved under the thawing, and consequent sea water spreading. The significant compositional irregularity of ionic compositional patterns in the thawed deposits is caused by differences in the particle size of sediments and hydrodynamics of the Arctic basin, and also can be explained by Quaternary eustatic events on the East Siberian Arctic shelf. Lithology, grain size and hydrological regime were considered to be the most important factors controlling concentration of sea water salt to thawed sediments. Over the roof of subsea permafrost in the Ivashkina Lagoon, the pronounced salinity maximum (50 g/L of Cl–) of interstitial water was observed. Consisting of moss debris, this segment promotes the accumulation of dissolved pore water compounds due to its high porosity and subsequent thawing of frozen rock.
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Drilling cores for this study were obtained during polar expeditions in 2014-2015 which were organised by the Pacific Oceanological Institute FEB RAS (Vladivostok), the National Research Tomsk Polytechnic University (Tomsk), and the Melnikov Permafrost Institute SB RAS (Yakutsk), in collaboration with Lomonosov Moscow State University (Moscow) and Shirshov Institute of Oceanology RAS (Moscow). Collection sites are located southeast of the Lena Delta near the Bykovsky Peninsula at the Buor-Khaya Bay. Unfrozen sediments were sampled with a steel spatula. Sampling of consolidated permafrost deposits from the drilling cores was carried out with the electric screwdriver and rathole bits. All samples were put into zip-lock polypropylene bags and kept frozen at –20 °C. Grain size of deposits were measured via low-angle laser light scattering in wet samples (approx. 20 g) using a Mastersizer 2000 particle analyser (Malvern Instruments, UK). Analytical conditions were 2000 rpm pump speed, 25 W ultrasound sonification power (40 KHz), 30 s exposition time for one measurement, and 2500 Hz scanning frequency. Milli-Q water was used as a dispersant and a blank. All laser diffraction analyses were done in triplicate and the results were averaged. The ionic composition of pore water was studied by aqueous extraction. Wet subsamples of deposits were dried with a MOC-120H moisture analyser (Shimadzu, Japan) at 105 °C for a constant mass. The dried samples (approx. 20 g) were placed into glass flasks and 150 ml Milli-Q water was added. Flasks with suspended samples were shaken with a Vortex Genius 3 shaker (IKA, Germany) for 15 min. Then, the water that was extracted was centrifuged using a 5702R centrifuge (Eppendorf, Germany) at 5500 rpm for 10 min to precipitate solids. Quantification of cations (sodium, potassium, calcium, magnesium) and anions (chlorides and sulfates) was performed in supernatants. The identification of anions was carried out by ion exchange chromatography with conductometric detection using a Dionex ICS-5000 analyser (Termo Scientific, USA) with pre-column and column PAX-100. A mix of carbonate buffer solution (3/4 mM of sodium carbonate/hydrocarbonate). Acetonitrile (5 %) was used as an eluent. Cations were quantified by atomic absorption spectrometry using a Solaar M spectrophotometer (Termo Scientific, USA). Water extracts were diluted in 100 times for Na+ and K+ quantification, in 20 times for Ca2+, and in 10 times for Mg2+ resulting analytical in an range from 1 to 30 mg/L. Wavelengths were 766.5 nm for potassium, 589.0 nm for sodium, 422.7 nm for calcium, and 285.2 for magnesium, flame – mix of acetylene and air. Spectral and chemical noise was eliminated by adding the buffer solutions: 0.1 % of Cs for K and 0.2 % of La for Ca and Mg. Precision for cations was at ≤ 10 %. The results were recalculated considering a dilution rate and moisture content, and expressed as g/L.