Features of the Elemental Composition of Aral Sea Suspended Matter in Modern Conditions

Abstract

The paper presents the first data on the contents of 22 macro- and microelements in marine suspended particulate matter (SPM) since the Aral Sea began to dry in 1961. The concentration of SPM in the western basin is low and fluctuates within a narrow range of 0.2 to 1.14 mg/L, on average, around 0.7 mg/L for 16 samples. Microscope studies have shown the presence of microparticles of different origin in SPM. Among the biogenic particles are diatomic opal frustules, individual coccoliths, plant pollen, etc. Terrigenous minerals are represented by grains of quartz, feldspars, amphiboles, pyroxenes, and clay aggregates. Chemogenic minerals include crystals of gypsum, celestine, and strontianite. Examination of unfiltered water under an optical microscope showed the presence of gypsum crystals, which points to authigenic mineral formation directly in the water column. The ICP-MS method (Agilent 7500) was used to analyze 11 samples of SPM from the 0–10 m layer (oxygenated waters) and five samples from the 18–38 m horizon (hydrogen sulfide water). With respect to the clay/shale global mean values, Aral Sea SPM is depleted in lithogenic Fe, Al, Ti, and Mg and somewhat enriched in Na and Mn. Comparison with data on the contents of the same elements in present-day Aral Sea sediments [1] has shown that SPM is notably poorer in bottom sediments of Ca, Mg, Fe, and M and enriched in Mn. With respect to clays/shales, Aral Sea SPM from oxygenated waters is enriched in Cu, Ni, Mo, Pb, and W (by 1.5–4.0 times), whereas SPM in the entire water column is notably depleted in Cr, Be, V, Zr, and Ta. Mo is sharply distinguished, with SPM from hydrogen sulfide waters enriched 37-fold; there are two reasons for this: hydrogen sulfide contamination and high water mineralization.